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Posted: 6/5/2013 8:56:00 PM EST
[Last Edit: 1/16/2014 6:52:23 PM EST by ZW17]
Link Posted: 6/5/2013 9:01:59 PM EST
Great info!!  MUCH appreciated you posting this!!!
Link Posted: 6/18/2013 10:36:43 PM EST
Good info.

My friend's Mom just had her HVAC unit replaced. 2400 sq ft house and the old unit was a 5 Ton unit. Contractor comes out and says I'm gonna put a 5 ton unit in there just like the old one.

When my friend told me that I thought a 5 ton unit was a little on the big side for that size house. My house in AL was 1875 sq ft and it had a 3.5 ton unit. Kept temperature just fine except on extremely hot days, but I was ok with that since it's better to be slightly undersized on the AC.

My friend asked the HVAC guy about doing a load calculation and he said that wouldn't be needed and if he did that the duct work would have to be re-sized blah blah blah. Anyway he installs 5 ton unit and my friend said the unit doesn't have that long of a cycle time. So, he's probably gonna have issues down the road. The condensate drain was installed wrong (water doesn't run up hill). His return was also sized too small. A 25"X25" filter is not big enough for a 5 ton unit. I told him to add another filter the same size on the other side of the return duct to get enough filter area. That would also cut down on the noise of the unit when it's running.

Link Posted: 7/8/2013 7:24:38 PM EST
Originally Posted By memsu:
Good info.

My friend's Mom just had her HVAC unit replaced. 2400 sq ft house and the old unit was a 5 Ton unit. Contractor comes out and says I'm gonna put a 5 ton unit in there just like the old one.

When my friend told me that I thought a 5 ton unit was a little on the big side for that size house. My house in AL was 1875 sq ft and it had a 3.5 ton unit. Kept temperature just fine except on extremely hot days, but I was ok with that since it's better to be slightly undersized on the AC.

My friend asked the HVAC guy about doing a load calculation and he said that wouldn't be needed and if he did that the duct work would have to be re-sized blah blah blah. Anyway he installs 5 ton unit and my friend said the unit doesn't have that long of a cycle time. So, he's probably gonna have issues down the road. The condensate drain was installed wrong (water doesn't run up hill). His return was also sized too small. A 25"X25" filter is not big enough for a 5 ton unit. I told him to add another filter the same size on the other side of the return duct to get enough filter area. That would also cut down on the noise of the unit when it's running.



I've never heard its better to be undersized, we're are you getting your info? If it cant keep up that is not ok, it's too small. Even on extremely hot days.
Link Posted: 7/17/2013 12:28:10 AM EST
Great write up!!! Everything that ZW17 says is absolutely true and great advice for a homeowner.

I'm an HVAC/R service tech by trade and work for a large company out of Rochester NY. I started out doing residential work but now I'm over to the commercial side of things and specialize in refrigeration. But all the same principles apply in both commercial and residential comfort cooling.

It absolutely is better to have an a/c slightly undersized rather than oversized. First you have to understand that there are 2 types of heat that a/c units are designed remove from your home....sensible heat and latent heat. Sensible heat is the temperature that you can actually measure with a thermometer. Latent heat refers to the humidity level. You can "feel" latent heat, but you cant measure it with a thermometer. Your thermostat measures sensible heat and uses that reading to cycle the unit on and off.

For example, a manual j load calculation determines you need 2.75 tons of a/c to properly cool your home. Manufacturers don't make 2.75 ton a/c systems. You would have to choose either 2.5 or 3 ton unit. You would get better performance out the 2.5 ton system and feel more comfortable. The reason being is that the oversized system will reach the "sensible heat" setpoint on your thermostat so fast, it doesnt give the system a chance to remove the "latent heat" from the house. You want the system to run longer. Running the unit longer will still bring the house down to temperature, but it will allow the system to draw more humidity out of the air. An oversized system will cause you to feel cold and clammy instead of cool and dry. 70 degree air with 80% humidity will "feel" warmer that 70 degree air with 15% humidity.

This is just a basic explanation and I pulled these numbers out of my ass, but hopefully it makes sense and you can begin to understand the basic principles of what you're trying to gain out of an a/c system. Bigger is not better and longer run times are a good thing for comfort cooling.

If any of you guys have any questions, you can always feel free to shoot me a pm too. I'll be glad to help out.
Link Posted: 7/25/2013 5:12:29 PM EST
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Originally Posted By BeardownAZ:


I've never heard its better to be undersized, we're are you getting your info? If it cant keep up that is not ok, it's too small. Even on extremely hot days.
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Originally Posted By BeardownAZ:
Originally Posted By memsu:
Good info.

My friend's Mom just had her HVAC unit replaced. 2400 sq ft house and the old unit was a 5 Ton unit. Contractor comes out and says I'm gonna put a 5 ton unit in there just like the old one.

When my friend told me that I thought a 5 ton unit was a little on the big side for that size house. My house in AL was 1875 sq ft and it had a 3.5 ton unit. Kept temperature just fine except on extremely hot days, but I was ok with that since it's better to be slightly undersized on the AC.

My friend asked the HVAC guy about doing a load calculation and he said that wouldn't be needed and if he did that the duct work would have to be re-sized blah blah blah. Anyway he installs 5 ton unit and my friend said the unit doesn't have that long of a cycle time. So, he's probably gonna have issues down the road. The condensate drain was installed wrong (water doesn't run up hill). His return was also sized too small. A 25"X25" filter is not big enough for a 5 ton unit. I told him to add another filter the same size on the other side of the return duct to get enough filter area. That would also cut down on the noise of the unit when it's running.



I've never heard its better to be undersized, we're are you getting your info? If it cant keep up that is not ok, it's too small. Even on extremely hot days.


An oversize unit doesn't run long enough to dehumidify. In the Southeast you want your unit to cool your house and get the humidity out. If your unit is too big it cools down the room too fast, but doesn't run long enough to bring the humidity down. You'll have a cool house, but it feels damp and is uncomfortable. Bring the humidity down and it feels much more comfortable even if its at the same temperature. A too big of a unit will also cycle more which can wear out equipment faster than one that has longer run times. Having a proper heat load calculation of your home will let you know what size unit you'll need.
Link Posted: 8/7/2013 4:11:24 PM EST
All excellent points here.  Newer construction is also tighter, meaning less infiltration/exfiltration and higher R values so both latent and sensible loads per square foot are lower.  This has resulted in many over-capacity installs, retrofits often base new units on the old size.  The retrofit tech who measures number, size, type and location of windows usually has a good idea of what size of unit you need. If they ignore the size of the old unit, you can be assured they won't over-size the calcs.



Nearly every condenser unit I have seen over the age of 5 years needs a good coil cleaning.  There is far more heat rejected here than at the evaporator yet they are often ignored.  Simple cleaner with brushing and a GENTLE flush (ordinary mains water pressure can bend fins or pins) usually yields a chocolate milk looking rinse water.  That dirt hinders heat rejection and efficiency.



Return air flow is a must.  Often, this is done by door gaps.  What happens when deep pile shag carpet is installed after?  Duct pressure goes up and seams pop.  Yuck, crawl space or attic work .



Finally, most new units have dual condensate drains.  For ground level installs, the emergency, high level drains are left plugged.  These drains SHOULD be used and connecting them is something the home owner can do.  Simple fittings and clear PVC hose will show if the primary has plugged.  If you don't, monthly wet vac of the drain line can save your expensive laminate floor .  Yep, I didn't remember and now have NEW stained and sealed CONCRETE floors.  After a month of work

       
 
Link Posted: 5/10/2014 9:59:19 PM EST
Off topic question.

How inefficient is an AC unit that was made in 2000? I live on post on Ft. Gordon and the AC unit works fine but I know it eats up electricity because I get a bill every month for it. I am not sure of my neighbors AC unit but they get a refund every month.
Link Posted: 7/4/2014 11:43:14 AM EST
I assume fried = burn out?
Link Posted: 7/4/2014 1:42:51 PM EST
Link Posted: 10/4/2014 1:17:59 PM EST
I'm in the process of buying a house.  The inspector told me that the furnace is dated 1990 and has an expected lifespan of about 25 years.

The sellers say that it has been served every fall, but haven't provided any documentation.  It seems to run fine, but the house has been unoccupied for about two years.

Obviously, I know you can't tell me much without an inspection, but should I be concerned that it is going to crap out on me?

Link Posted: 10/4/2014 1:31:25 PM EST
[Last Edit: 10/4/2014 1:34:02 PM EST by ZW17]
Link Posted: 10/4/2014 1:54:13 PM EST
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Originally Posted By ZW17:
Apg11...

First you have an oil fired hot water boiler system, not a forced air furnace.

Being that the home was unoccupied for two years in NYS and assuming the heating system was turned off I would be very concerned. I would be worried that the boiler loop (hot water piping) wasn't drained properly and has potential freeze damage. To prevent freezing in such a system you would need to open the loop, drain it, and then blow it out with compressed air, much like an outdoor irrigation system every fall. The other option would be to add glycol antifreeze but it would have to be nearly 100% concentration, then it would be good down to -20*F if I remember correctly.

I would want proof that it was handled correctly and I would hire a certified oil burner boiler tech (not a home inspector) to go over the system with a fine tooth comb (less than $300).

Hope this helps.

ETA... 25yrs is nothing for a hot water boiler. I have seen plenty of residential boilers last 40+yrs. Not much to them and everything on them is replaceable. Not the most efficient for sure, but they are tanks and last forever with a little TLC once a year.
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Right, my mistake, it is a boiler.

We have confirmed that the boiler is functioning properly and the water is flowing to all zones.  That would confirm that there is no freeze damage, no?

We are also considering adding a separate water heater since we use a lot of hot water.

Thanks for your help!  This is my first experience with an oil burner.
Link Posted: 12/1/2014 2:29:31 PM EST
[Last Edit: 12/1/2014 2:58:23 PM EST by Defcon]


This is a great thread.  Thanks so much.  I have 2 companies coming out to give me a estimate on a new system.  One is a Lennox dealer the other is a Bryant/Goodman/Carrier/Payne and Amana.





I will be curious to see if they volunteer to do a manual J.  





Do you have any brands you suggest I avoid all together?







This is for my main residence which was built in mid-1990's.


 
Link Posted: 2/4/2015 7:30:53 PM EST
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Originally Posted By svtfast:
Off topic question.

How inefficient is an AC unit that was made in 2000? I live on post on Ft. Gordon and the AC unit works fine but I know it eats up electricity because I get a bill every month for it. I am not sure of my neighbors AC unit but they get a refund every month.
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Anyone?
Link Posted: 2/4/2015 11:12:58 PM EST
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Originally Posted By svtfast:




Anyone?
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Originally Posted By svtfast:
Originally Posted By svtfast:
Off topic question.

How inefficient is an AC unit that was made in 2000? I live on post on Ft. Gordon and the AC unit works fine but I know it eats up electricity because I get a bill every month for it. I am not sure of my neighbors AC unit but they get a refund every month.




Anyone?


I'm gonna assume that your 2000 AC system is a 10 seer unit. But that number is not the be-all end-all number that determines how efficient your system is running. Obviously a new system with a high seer rating uses less electricity to achieve the same result. But there are a lot more factors that contribute to the total cost of operation. A high seer rating doesn't mean squat unless the whole system is sized properly (duct work, evaporator coil, furnace, thermostat, etc.) You can throw all the potential savings right out the window unless you treat the system as a whole and every aspect is addressed  The posts above touch base on many things you need to consider for getting the most bang for your buck.

I'm sorry this advice is pretty general and doesn't answer your question directly. You should start a new thread so we can try to help you individually with your specific situation. Include the make and model of your system (furnace and AC). What type of filtration? Has everything been maintained on a regular basis? Do you have the coils washed every year? Include pictures too. The more info the better.

Link Posted: 2/4/2015 11:48:46 PM EST
[Last Edit: 2/4/2015 11:50:25 PM EST by pvc1984]
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Originally Posted By Defcon:
This is a great thread.  Thanks so much.  I have 2 companies coming out to give me a estimate on a new system.  One is a Lennox dealer the other is a Bryant/Goodman/Carrier/Payne and Amana.

I will be curious to see if they volunteer to do a manual J.  

Do you have any brands you suggest I avoid all together?



This is for my main residence which was built in mid-1990's.

 
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First, I would recommend getting a 3rd and maybe even a 4th company to come out to give you a quote. Make sure they're established companies with a decent size clientele and not some fly-by-night outfit.

Second, the quality of the install is way more important than brand name of the equipment you buy.

IMO, out of the brand names that you mentioned, I would suggest a Goodman system. The warranty that Goodman offers is second to none. Replacement parts are readily available and generally cheaper than Carrier or Lennox parts.

Another brand I would recommend is Rheem. Their equipment is nice, easy to work on, and parts are readily available. Ruud is another one to consider. Ruud is made by Rheem, they use the same parts, and they're generally cheaper. If Rheem is GMC, then Ruud would be Chevy.

I would avoid getting Lennox. Replacement parts are usually more expensive and take longer to get. At least in my neck of the the woods (Rochester NY). I would also avoid York. Their 90% furnaces are a real pain to work on.

Bottom line, don't pick the low bidder and don't pick the most expensive contractor. I would pick a contractor that is middle of the road or middle-high. And I would personally go with a Goodman system for the most bang for the buck.

ETA: Just noticed you posted that back in the beginning of December. Probably a little late by now. What did you end up going with?
Link Posted: 2/5/2015 8:03:16 PM EST
[Last Edit: 2/5/2015 8:04:33 PM EST by Defcon]

Thank you for the reply.


       



I fixed my current furnace and am in the decision phase still.





One guy says 100K BTU the other says 80K BTU unit.  In the end, I had both bid exact same Bryant units.  Both bid the 80K and the 100K.   The cheaper guy is good but he insists I don't need a 100K BTU unit but says if we have a cold snap of -25 the 80K may run all day and all night and may not keep the house at 70deg.  He thinks it may drop to 67 or so.  We have had a -23 day here do far so it can and will happen at some point.  





Both of them are top quality and I have personally seen them each install new units.  Their work was excellent in my opinion.  I guess I haven't acted because the 80 vs 100 is killing me inside and I don't think either has convinced me their #s are right.  As a homeowner, I kind of feel paralyzed.  The price difference is enough to make me pause.  I want to do what is right by my family and ensure proper sizing for the home.  80K guy did a manual J but he didn't go in the attic where I think I have low R-Value.  I told him of this but he said it wouldn't make that much of a difference in the model.  He even changed it and said it didn't push it over the edge.





The whole situation kind of sucks from my standpoint.





I am looking at 98% eff units mostly with scalable heating and modulating fans.  Comfort to me is a major consideration.  I have spent years being slightly cold in houses I have owned.  I don't want to deal with that as I get older. Any more advice is appreciated.




 
Link Posted: 5/22/2015 7:45:15 AM EST
I wish I saw this sooner

My parents have a company coming to install a system in their house next week.  The house was built with electric ceiling heat and no A/C....so ductwork and everything are going to have to be installed...
Link Posted: 5/27/2015 6:27:51 PM EST
Looks like this was written very shortly after I replaced my complete system. This would have been helpful for sure.

One point...Not disputing the value of anything ZW17 wrote, but practically speaking you'll be doing all that shopping and quote comparison *after* your unit goes out and when its 100+ outside. It will definitely influence your choice.
Link Posted: 5/27/2015 6:42:18 PM EST
all my customers love their variable drive units, lower electric bills, low humidity and a more constant even air temperature throughout the home.





Link Posted: 8/20/2015 6:58:09 PM EST
Can anyone tell me how to clean in the indoor coil? System keeps on freezing up. All that is left is the thermal expansion valve. I think the coil could use a wash.
Link Posted: 8/20/2015 7:37:22 PM EST
Link Posted: 8/20/2015 8:53:06 PM EST
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Originally Posted By ZW17:


I'd be glad to, start a new thread and we can chat about it there.
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Originally Posted By ZW17:
Originally Posted By svtfast:
Can anyone tell me how to clean in the indoor coil? System keeps on freezing up. All that is left is the thermal expansion valve. I think the coil could use a wash.


I'd be glad to, start a new thread and we can chat about it there.



Ok will do. I took some pictures of the unit but its late (for me) so I am off to bed. I will try to post the pics in a new thread tomorrow.

Thanks!

Link Posted: 12/27/2015 1:49:03 AM EST
[Last Edit: 12/27/2015 1:59:03 AM EST by AR15Texan]
If you do have diagnostics done or even pre-season checkups make sure you get your refrigerant high/low pressures, superheat and/or subcooling temps, dry/wet bulb measurements, blower capacitor reading, compressor amp draw, condenser fan amp draw, etc.

It's also a good idea to make notes about your system's sequence of events and time/duration of each event when you call for heat or cool.  For example, how long does the exhaust fan run before the ignitor lights.  Learn your systems operation while it works will aid in troubleshooting when it finally doesn't work.  

Purchase some replacement parts ahead of time if you venture to DIY.  Condenser relay, condenser and blower capacitors, ignitor, flame sensor, and maybe even a controller board.  Above all maintenance change those filters regularly.
Link Posted: 12/31/2015 11:12:56 PM EST
I just purchased a home that was built in 1971.  It was a one owner home and the guy never installed an HVAC system, so we have to install one.

The home has a full basement (1,500+ square feet) that will be finished and another 1,700 square feet on the first floor, no second floor.  Brick veneer.

What are your thoughts and recommendations on a geothermal heat pump?
Link Posted: 5/10/2016 7:05:04 PM EST
thanks for posting this,  my ac is at the 8 year mark and about ready to be replaced.





Link Posted: 6/10/2016 8:17:28 AM EST
Is there any advantage to replacing/upgrading ductwork?  

We've got a 1959 ranch house with a full basement.  +/- 1,000 sf on each level.  Upstairs is your basic 3 bedroom/2 bathroom space.  The basement is mostly finished, and includes the garage, laundry room, and a den, bath, and guest BR.  Not full height - we probably have a little under 8' of height floor to ceiling in the basement.  Full brick exterior, and the basement walls are CMU.  We're going to be re-doing most of the basement - pretty much a full gut job.  We're in this house for the long-term - I wouldn't be surprised if I spend the next 25 years here (I'm 45).  Single-zoned HVAC system, so pretty basic.

Would there be any real advantage to tearing out the original-to-the-house ductwork while we're doing everything else?  Are the systems that much better, or could we go to something that takes up less space?
Link Posted: 6/10/2016 8:26:22 AM EST
Is R12 being outlawed by 2020?
Link Posted: 6/10/2016 3:22:31 PM EST
Link Posted: 6/11/2016 9:20:02 PM EST
Right now I have a 30ish year old oil-fired forced-air furnace in a ~2,000sqft house.  It works fine but I imagine a newer one would be much more efficient.  We want to add central-air which I'm sure would necessitate a new furnace, anyway.  Assuming there's no major issues with the duct-work, how badly is this going to hurt the savings account?  We plan on staying with oil heat (still have over 300 gallons in the tank from last winter ) unless doing so would add significant costs.  No natural gas to the home but we do have 200amp electric service.
Link Posted: 6/11/2016 10:24:54 PM EST
unless you live on a lake that you can put a closed loop in, run away.
Link Posted: 6/22/2016 9:21:07 PM EST
Modulating condensing boilers, thoughts from a self declared expert.

They are most efficient and get their 96% rating with 90 degree return water.

Oversizing will leave you with a minimum firing rate more than the heat loss on design day and will hurt performance.
My original 140k boiler was replaced with a 55k unit, the smallest one they make.  It has 5:1 turndown of the firing rate. The new ones are 10:1 but pricier.

So if you have one installed, and they set it to 180 degrees like the old iron boiler it will never condense, and be only about 85% efficient.

You must set the out door reset curve to maximize eficency. This will set the water temp based on the outdoor temperature.  I was able to set mine to range from 160 to 115 with fin tube baseboard.  At 35 degrees my return water temps were at 108 degrees. When it hit -10 the water temp was at 150.

It won't condense in the very cold temps but it will lower the firing rate to maintain the water temp. The boiler will run for hours at a time just matching the heat loss of the building and turning off when solar gain raises the temperature.  Depending on the temp it will run from 20 to 45 percent.  

I use the thermostat as the high limit basically. No setbacks. The boiler has a boost feature if you really want to set it back. But you program it in the boiler, not the t stat.

Micro zoning will wear out these boilers fast if there is not enough radiation. They will short cycle constantly. There is more maintenance for these units, especially the water tube design, aka gionni heat exchanger(spelled wrong probably). I went with the firetube design and it is more better.

These work best with cast iron radiators where there is a high mass . it will also work on fin tube baseboard too, but you need a decent length. I merged both my zones for a 95 ft of baseboard run.  

Link Posted: 3/5/2017 11:53:27 AM EST
We have mild summers with low humidity so we are not interested in AC, but I would like to get a new heat furnace as this one is somewhere between 15-20 years old.

Is a heat only system any cheaper in both parts and installation than a combination AC/heat unit?

We have lived here 12 years and have never turned on the AC unit.
Link Posted: 3/10/2017 5:54:53 PM EST
We have 12 year old unit running on the R22 freon that has a slow leak.  Every year or two, we have to have it charged.  Cheap because we had a connection.  The motor needs replacing now at about $150 plus labor.  But, we still have the leak once that is fixed.  Our connection says after our next charge he will be out of our freon, so we think at that point it may be impossible to continue charging it.

I'm feeling we should just buy once cry once and buy a new system?  The leak will be $& to find we are told so that's why we haven't looked for it.

Do you agree it's just best to go ahead and buy rather than buying the motor and continuing to try to charge?  If so, going to look at Trane, Carrier and American Standard for bids. Although I know zero about this, your pinned post was helpful and maybe can get me to a goos point if we buy.  Thanks!
Link Posted: 3/10/2017 6:17:48 PM EST
Very good advice, we have a home that was built in 2004 with Lennox equipment (builders grade I am sure). The home is 3200 square feet two story. A while back our downstairs unit quit working ( outside unit fan would not come on).  Called a national known A/C repair service to come out and look at it. He diagnosed a bad capacitor on the fan motor. Wanted $600 to replace it, which I thought was insane. I paid him his diagnostic fee and sent him on his way. Called a friend of mine who is a A/C repairman and explained what was happening. He laughed so hard it wasn't funny. He said he could buy a capacitor for under $50. He lives out of town so he called a local A/C supply house and had me pick up a capacitor. I replaced it myself in about an hour (making sure I didn't screw up).

Vince
Link Posted: 3/28/2017 12:50:49 AM EST
[Last Edit: 3/28/2017 1:00:58 AM EST by Thump_rrr]
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Originally Posted By pvc1984:
Great write up!!! Everything that ZW17 says is absolutely true and great advice for a homeowner.

I'm an HVAC/R service tech by trade and work for a large company out of Rochester NY. I started out doing residential work but now I'm over to the commercial side of things and specialize in refrigeration. But all the same principles apply in both commercial and residential comfort cooling.

It absolutely is better to have an a/c slightly undersized rather than oversized. First you have to understand that there are 2 types of heat that a/c units are designed remove from your home....sensible heat and latent heat. Sensible heat is the temperature that you can actually measure with a thermometer. Latent heat refers to the humidity level. You can "feel" latent heat, but you cant measure it with a thermometer. Your thermostat measures sensible heat and uses that reading to cycle the unit on and off.

For example, a manual j load calculation determines you need 2.75 tons of a/c to properly cool your home. Manufacturers don't make 2.75 ton a/c systems. You would have to choose either 2.5 or 3 ton unit. You would get better performance out the 2.5 ton system and feel more comfortable. The reason being is that the oversized system will reach the "sensible heat" setpoint on your thermostat so fast, it doesnt give the system a chance to remove the "latent heat" from the house. You want the system to run longer. Running the unit longer will still bring the house down to temperature, but it will allow the system to draw more humidity out of the air. An oversized system will cause you to feel cold and clammy instead of cool and dry. 70 degree air with 80% humidity will "feel" warmer that 70 degree air with 15% humidity.

This is just a basic explanation and I pulled these numbers out of my ass, but hopefully it makes sense and you can begin to understand the basic principles of what you're trying to gain out of an a/c system. Bigger is not better and longer run times are a good thing for comfort cooling.

If any of you guys have any questions, you can always feel free to shoot me a pm too. I'll be glad to help out.
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You can sure a hell measure latent heat with a thermometer.
It's called a wet bulb thermometer.
That and your psychrometric chart will give you the answer.
Mechanical contractor, 30 years in the business next month.
I do primarily commercial, industrial.
Link Posted: 4/30/2017 8:42:25 PM EST
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Originally Posted By memsu:
An oversize unit doesn't run long enough to dehumidify. In the Southeast you want your unit to cool your house and get the humidity out. If your unit is too big it cools down the room too fast, but doesn't run long enough to bring the humidity down. You'll have a cool house, but it feels damp and is uncomfortable. Bring the humidity down and it feels much more comfortable even if its at the same temperature. A too big of a unit will also cycle more which can wear out equipment faster than one that has longer run times. Having a proper heat load calculation of your home will let you know what size unit you'll need.
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Originally Posted By memsu:
Originally Posted By BeardownAZ:
Originally Posted By memsu:
Good info.

My friend's Mom just had her HVAC unit replaced. 2400 sq ft house and the old unit was a 5 Ton unit. Contractor comes out and says I'm gonna put a 5 ton unit in there just like the old one.

When my friend told me that I thought a 5 ton unit was a little on the big side for that size house. My house in AL was 1875 sq ft and it had a 3.5 ton unit. Kept temperature just fine except on extremely hot days, but I was ok with that since it's better to be slightly undersized on the AC.

My friend asked the HVAC guy about doing a load calculation and he said that wouldn't be needed and if he did that the duct work would have to be re-sized blah blah blah. Anyway he installs 5 ton unit and my friend said the unit doesn't have that long of a cycle time. So, he's probably gonna have issues down the road. The condensate drain was installed wrong (water doesn't run up hill). His return was also sized too small. A 25"X25" filter is not big enough for a 5 ton unit. I told him to add another filter the same size on the other side of the return duct to get enough filter area. That would also cut down on the noise of the unit when it's running.
I've never heard its better to be undersized, we're are you getting your info? If it cant keep up that is not ok, it's too small. Even on extremely hot days.
An oversize unit doesn't run long enough to dehumidify. In the Southeast you want your unit to cool your house and get the humidity out. If your unit is too big it cools down the room too fast, but doesn't run long enough to bring the humidity down. You'll have a cool house, but it feels damp and is uncomfortable. Bring the humidity down and it feels much more comfortable even if its at the same temperature. A too big of a unit will also cycle more which can wear out equipment faster than one that has longer run times. Having a proper heat load calculation of your home will let you know what size unit you'll need.
While the unit should be sized correctly, why couldn't you just slow down the fan?  This would get the temperature of the air leaving the coil at a lower temperature and therefore a lower dewpoint.  It would be less efficient, but it could band-aid a poor installation.
Link Posted: 4/30/2017 8:43:42 PM EST
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Originally Posted By ZW17:
Negative. R12 has been outlawed since 1996.

R22 was the R12 replacement, right now R22 is in a phase out by the EPA.

18 million pounds of new and imported R-22 will be allowed in 2016, 13 million pounds in 2017, 9 million pounds in 2018, and 4 million pounds in 2019. No new or imported R-22 will be allowed in the U.S. on or after Jan. 1, 2020.

Prices are beginning to reflect this.

R410a is the R22 replacement.
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Originally Posted By ZW17:
Originally Posted By Drsalee:
Is R12 being outlawed by 2020?
Negative. R12 has been outlawed since 1996.

R22 was the R12 replacement, right now R22 is in a phase out by the EPA.

18 million pounds of new and imported R-22 will be allowed in 2016, 13 million pounds in 2017, 9 million pounds in 2018, and 4 million pounds in 2019. No new or imported R-22 will be allowed in the U.S. on or after Jan. 1, 2020.

Prices are beginning to reflect this.

R410a is the R22 replacement.
R12 was automotive.  It was replaced by R134a.
Link Posted: 5/5/2017 10:17:28 PM EST
I have a rheem system in a house i just bought that is 2.5 tons. The house is 3 stories including 1/2 finished basement, 3800 sq/ft total.  Not sure how old the system is because the label is completely faded, but at least 10 years. The only thermostat is on the main floor. The basement stays freezing cold when the thermostat is set to 70, the mail floor stays at 70 and the upstairs where the bed rooms are is at least 76 or higher depending on outside temp. House was built in 1951. I'm not going to make it thru the summer sweating my ass off while trying to sleep. A window shaker is not an option. What's the correct way to fix this situation?
Link Posted: 5/6/2017 3:11:07 AM EST
Link Posted: 5/6/2017 6:42:48 AM EST
[Last Edit: 5/6/2017 6:43:18 AM EST by 03PSD]
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Originally Posted By ZW17:
Get an air balance done.
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Originally Posted By ZW17:
Originally Posted By 03PSD:
I have a rheem system in a house i just bought that is 2.5 tons. The house is 3 stories including 1/2 finished basement, 3800 sq/ft total.  Not sure how old the system is because the label is completely faded, but at least 10 years. The only thermostat is on the main floor. The basement stays freezing cold when the thermostat is set to 70, the mail floor stays at 70 and the upstairs where the bed rooms are is at least 76 or higher depending on outside temp. House was built in 1951. I'm not going to make it thru the summer sweating my ass off while trying to sleep. A window shaker is not an option. What's the correct way to fix this situation?
Get an air balance done.
I would assume this requires ducts that can be shut off or throttled back? Im not sure i have that. Is 2.5 tons sufficient for 3800 sq ft?
Link Posted: 5/6/2017 9:12:52 AM EST
Link Posted: 6/2/2017 2:46:57 PM EST
This would have been awesome for my parents to read, they had a motherboard go out on their furnace and they dropped something like 8 grand for a new furnace with a bunch of add-ons that I don't think they needed. For that price they probably could have been close to getting air conditioning added to their house.
Link Posted: 7/12/2017 7:58:11 AM EST
I hope this would be considered the right place to post this.

2600ft^2 house, two AC units, ground mounted.  Date of MFG on said units is Jan/09.  They are WeatherKing, if it matters.  Large unit does the downstairs, smaller unit does the upstairs.

Downstairs stopped blowing cold air last night.  Standing next to the unit, the fan spins, but the compressor motor is very obviously the problem -- loud 1-second hum, followed by 5 or 6 seconds of silence, followed by loud 1-second hum, rinse and repeat.  Seems the motor is trying to start, but cannot.

I am hoping this will be something simple like a capacitor.  This is my first experience with a bad HVAC system and I hope to avoid the pitfalls mentioned by the OP (thanks OP, you are a Godsend).  

Questions... Is my motor completely fried, or is it worth trying to replace a cheap capacitor?  Replacement compressors (online research) are in the $700 range.

I know I am already out of my element, so a service call might be in the very near future anyway, however I am confident I can replace a capacitor if that would a> fix it b> rule out the problem if the part is cheap enough c> etc

I read the "why put a new part in a 15-year old system" listed above... But this is AZ, where the "8 year lifespan" comes into play.  The units are 8 years old.  So now I am on the fence.  Fix or replace?

I know the upstairs unit will be working overtime as the heat form downstairs rises... I have a few fans on the staircase to try to direct some cooler air downstairs (dogs, kids, etc).  Given this is the HVAC guys' busiest time of year, and I may be looking at a few days/week before a guy can come out and take a look, is it appropriate to shut down the upstairs unit and suffer the heat, or let it run and hope that the extra workload doesn't kill it outright?

Suggestions welcome, and thanks.
Link Posted: 7/12/2017 9:37:25 PM EST
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Originally Posted By tucansam:
I hope this would be considered the right place to post this.

2600ft^2 house, two AC units, ground mounted.  Date of MFG on said units is Jan/09.  They are WeatherKing, if it matters.  Large unit does the downstairs, smaller unit does the upstairs.

Downstairs stopped blowing cold air last night.  Standing next to the unit, the fan spins, but the compressor motor is very obviously the problem -- loud 1-second hum, followed by 5 or 6 seconds of silence, followed by loud 1-second hum, rinse and repeat.  Seems the motor is trying to start, but cannot.

I am hoping this will be something simple like a capacitor.  This is my first experience with a bad HVAC system and I hope to avoid the pitfalls mentioned by the OP (thanks OP, you are a Godsend).  

Questions... Is my motor completely fried, or is it worth trying to replace a cheap capacitor?  Replacement compressors (online research) are in the $700 range.

I know I am already out of my element, so a service call might be in the very near future anyway, however I am confident I can replace a capacitor if that would a> fix it b> rule out the problem if the part is cheap enough c> etc

I read the "why put a new part in a 15-year old system" listed above... But this is AZ, where the "8 year lifespan" comes into play.  The units are 8 years old.  So now I am on the fence.  Fix or replace?

I know the upstairs unit will be working overtime as the heat form downstairs rises... I have a few fans on the staircase to try to direct some cooler air downstairs (dogs, kids, etc).  Given this is the HVAC guys' busiest time of year, and I may be looking at a few days/week before a guy can come out and take a look, is it appropriate to shut down the upstairs unit and suffer the heat, or let it run and hope that the extra workload doesn't kill it outright?

Suggestions welcome, and thanks.
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There is a fair chance it is a capacitor.  Turn off the power to the unit and look at the rating on the capacitor and order a new one.  You can get them from Amazon.  If it doesn't work you are out maybe $20.
Link Posted: 7/12/2017 10:29:51 PM EST
Thanks, further research indicates the exact same thing.  Hoping to test the cap tomorrow and get one ordered ASAP.  Luckily we have two AC units in the house so the need is not dire, however I am making the family run the second unit only periodically so as not to stress it and they are NOT happy, ha.
Link Posted: 7/21/2017 11:42:11 PM EST
[Last Edit: 7/21/2017 11:48:59 PM EST by Gyprat]
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Originally Posted By tucansam:
I hope this would be considered the right place to post this.

2600ft^2 house, two AC units, ground mounted.  Date of MFG on said units is Jan/09.  They are WeatherKing, if it matters.  Large unit does the downstairs, smaller unit does the upstairs.

Downstairs stopped blowing cold air last night.  Standing next to the unit, the fan spins, but the compressor motor is very obviously the problem -- loud 1-second hum, followed by 5 or 6 seconds of silence, followed by loud 1-second hum, rinse and repeat.  Seems the motor is trying to start, but cannot.

I am hoping this will be something simple like a capacitor.  This is my first experience with a bad HVAC system and I hope to avoid the pitfalls mentioned by the OP (thanks OP, you are a Godsend).  

Questions... Is my motor completely fried, or is it worth trying to replace a cheap capacitor?  Replacement compressors (online research) are in the $700 range.

I know I am already out of my element, so a service call might be in the very near future anyway, however I am confident I can replace a capacitor if that would a> fix it b> rule out the problem if the part is cheap enough c> etc

I read the "why put a new part in a 15-year old system" listed above... But this is AZ, where the "8 year lifespan" comes into play.  The units are 8 years old.  So now I am on the fence.  Fix or replace?

I know the upstairs unit will be working overtime as the heat form downstairs rises... I have a few fans on the staircase to try to direct some cooler air downstairs (dogs, kids, etc).  Given this is the HVAC guys' busiest time of year, and I may be looking at a few days/week before a guy can come out and take a look, is it appropriate to shut down the upstairs unit and suffer the heat, or let it run and hope that the extra workload doesn't kill it outright?

Suggestions welcome, and thanks.
View Quote
Most likely it's a bad capacitor. It happens a lot. Both of my AC units are equipped with running capacitors. I have once noticed that the downstairs AC was not cooling as much as it used to. Several weeks later it stopped working at all. I replaced the running capacitor and everything is back to normal. I checked the capacitor in the other AC unit and it looked a little bloated too. I replaced it as well and the unit is working better now.
Usually I try to replace running caps every 5 years to improve performance and efficiency. It's a cheap preventive maintenance item and will save money on electric bill and most likely will extend AC life by reducing operating temperatures.
Some motors are equipped with starting capacitors only. In this case, the capacitor is only used for a fraction of a second at every motor start. Replacing a starting cap will not improve efficiency.

Also, look at installing a whole house surge protector at the main electrical panel. A decent unit can be bought for several hundred dollars and they are very easy to install. This will protect your expensive appliances from damage. Can't afford one? Get a relatively inexpensive surge protector that fits into a "dual breaker" spot in your breaker panel. They sell for around $60. It won't protect from a direct lightning strike but will protect your system from transients, voltage spikes/surges.
Link Posted: 8/7/2017 1:00:12 PM EST
[Last Edit: 8/9/2017 7:07:58 PM EST by Riley1980]
Paging @ZW17 (or other's who know more than I)

Just want to bounce an issue off of you.

I'm dealing with a carrier RTU. Tstat was dead when I arrived, found 5amp fuse blown on the board. Replaced it and the blower would run, but fuse would pop right as the call for cooling came through. Contractor, board, transformer, and stat wire are good. I can't tell if the tstat itself is shorting to ground though.

Ohm'd the compressor and it seemed fine, same with condenser fan.

Obviously there is a short on the control side somewhere, or a component is pulling very high amps..

I'd love your opinion on it.

Thanks.


ETA: thanks for the IM's guys. I did find the issue. Traced Y1 all the way to the blower motor, (which had a broken mount) where it had vibrated to the point of short right at the motor. Was a PITA to find. Fixed short, put in a T&M bid for blower assembly.
Cheers!
Link Posted: 8/9/2017 7:10:03 PM EST
Only took this many times to find it.

Link Posted: 10/8/2018 10:51:37 PM EST
I moved into a house last year, the natural gas furnace is 25 years old, the AC is 13 years old.  The first HVAC contractor to look at the furnace said the heat exchanger was cracked and needed to be replaced immediately. Second guy said that the furnace looked ok (some hairline cracks on heat exchanger, but a steady, blue flame), but that the AC was running low on R22. We decided to try to buy some CO detectors and try to make it through a winter and summer, which we have done. But now, the question is, should we replace everything, or wait until something breaks. I'm tempted to replace the AC since (if it's already low on R22) - the costs to refill are going to be significant.
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