[ARCHIVED THREAD] - AC question (Page 1 of 2)
Posted: 6/30/2013 12:11:28 PM EDT
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We just bought this house a few months ago and the AC unit is undersized. The house is well insulated but has a huge window and high ceilings on the main floor. The basement stays cold while the main floor gets hot. Even with the ac kicking on at 10:00 am when it's cool out the unit isn't able to cool off the main floor and runs all day. In fact when it cools off at night we are better off shutting down the system and opening the windows. We have a nice furnace with a variable speed blower so I don't understand why they undersized the AC unit. Is there anything else that we could try?
We were quoted around $3000.00 to replace this unit with a 3.5 ton 13 seer that included cleaning and reusing our existing line set. This seems high to me. I thought about putting a ceiling fan in the great room to help push some of the hot air off and increase the cooling but I doubt that will help the AC unit cycle. |
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Have you shut most, maybe all, of the vents in the basement and then open up the ones all the way upstairs to see if that will help before laying out that cash first? I was told by the HVAC technician not to do that. That by closing off the vent it would wreck the efficiency of the system and wouldn't cool as well. |
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Have you shut most, maybe all, of the vents in the basement and then open up the ones all the way upstairs to see if that will help before laying out that cash first? I was told by the HVAC technician not to do that. That by closing off the vent it would wreck the efficiency of the system and wouldn't cool as well. Sounds like it isn't cooling well already. What do you have to lose? |
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First... What makes you believe your system is undersized? Was a proper heat loss/heat gain survey performed to prove it was undersized or did a tech tell you this?
Second... Have you ever had your ducting professionally balanced? Proper airflow calculated and adjusted to the room sizes? Third.... Have you had your system checked to insure it's working at it's peak performance? If so, do you have documentation of superheat, subcooling, delta T, pressures, amps/volts, blower CFM? |
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Quoted: Can you please drive up here, and do all this to my house and A/C? Pretty please? First... What makes you believe your system is undersized? Was a proper heat loss/heat gain survey performed to prove it was undersized or did a tech tell you this? Second... Have you ever had your ducting professionally balanced? Proper airflow calculated and adjusted to the room sizes? Third.... Have you had your system checked to insure it's working at it's peak performance? If so, do you have documentation of superheat, subcooling, delta T, pressures, amps/volts?  |
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We just bought this house a few months ago and the AC unit is undersized. The house is well insulated but has a huge window and high ceilings on the main floor. The basement stays cold while the main floor gets hot. Even with the ac kicking on at 10:00 am when it's cool out the unit isn't able to cool off the main floor and runs all day. In fact when it cools off at night we are better off shutting down the system and opening the windows. We have a nice furnace with a variable speed blower so I don't understand why they undersized the AC unit. Is there anything else that we could try? We were quoted around $3000.00 to replace this unit with a 3.5 ton 13 seer that included cleaning and reusing our existing line set. This seems high to me. I thought about putting a ceiling fan in the great room to help push some of the hot air off and increase the cooling but I doubt that will help the AC unit cycle. I am in the exact same boat, OP. I have had 4 different HVAC companies out here and they all say the thing is undersized. I continue to doubt them only because my neighbor has the identical floor plan/square feet, and the same unit (size, model, etc...) and her house gets to 67 if she sets the thermostat to that. We bought the house 3 years ago, built in 2002. Yesterday, I set ours at 69, and it got to 81! Two companies have quoted anywhere from 3-5K for a new unit. I sure as hell don't want to spend that on an AC. Kind of funny, I just dropped 3700 on a new JP LRP-07 I had no qualms doing that, didn't even think twice! You guys know I have my priorities straight at least!
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Can you please drive up here, and do all this to my house and A/C? Pretty please? First... What makes you believe your system is undersized? Was a proper heat loss/heat gain survey performed to prove it was undersized or did a tech tell you this? Second... Have you ever had your ducting professionally balanced? Proper airflow calculated and adjusted to the room sizes? Third.... Have you had your system checked to insure it's working at it's peak performance? If so, do you have documentation of superheat, subcooling, delta T, pressures, amps/volts?
Size your own damn it!
HVAC LOAD CALC |
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First... What makes you believe your system is undersized? Was a proper heat loss/heat gain survey performed to prove it was undersized or did a tech tell you this? Second... Have you ever had your ducting professionally balanced? Proper airflow calculated and adjusted to the room sizes? Third.... Have you had your system checked to insure it's working at it's peak performance? If so, do you have documentation of superheat, subcooling, delta T, pressures, amps/volts, blower CFM? 1. The HVAC tech that came out to look at why it isn't shutting down or able to cool off the upstairs said it was probably undersized. He said that if everything was perfect it might would work but it would never be able to strip the heat out of the house if we let it get to warm. 2. No we just bought the house. it was built in 2003 so I don't know if it was ever tested. 3. The tech that came out a month ago tested the system pressures and temps at both the unit and the vents.He did a few other things but I have no Idea what it was. He did say that he thought it was slightly over pressured and got that number down to spec. He was unsure about adjusting the blower speed do to not having a manual for our brand and model. |
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Get some shade on that big window, an awning is the most effective thing, lower on the list is some kind of reflective film, but it you can keep the sun from hitting that big window at all, that's the most effective thing. The big window has tinted low e glass. In fact it doesn't feel any hotter next to the window. |
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We just bought this house a few months ago and the AC unit is undersized. The house is well insulated but has a huge window and high ceilings on the main floor. The basement stays cold while the main floor gets hot. Even with the ac kicking on at 10:00 am when it's cool out the unit isn't able to cool off the main floor and runs all day. In fact when it cools off at night we are better off shutting down the system and opening the windows. We have a nice furnace with a variable speed blower so I don't understand why they undersized the AC unit. Is there anything else that we could try? We were quoted around $3000.00 to replace this unit with a 3.5 ton 13 seer that included cleaning and reusing our existing line set. This seems high to me. I thought about putting a ceiling fan in the great room to help push some of the hot air off and increase the cooling but I doubt that will help the AC unit cycle. I am in the exact same boat, OP. I have had 4 different HVAC companies out here and they all say the thing is undersized. I continue to doubt them only because my neighbor has the identical floor plan/square feet, and the same unit (size, model, etc...) and her house gets to 67 if she sets the thermostat to that. We bought the house 3 years ago, built in 2002. Yesterday, I set ours at 69, and it got to 81! Two companies have quoted anywhere from 3-5K for a new unit. I sure as hell don't want to spend that on an AC. Kind of funny, I just dropped 3700 on a new JP LRP-07 I had no qualms doing that, didn't even think twice! You guys know I have my priorities straight at least!I kind of went through this, but my house was designed for exactly what I wanted and what it should have been. What is the outdoor temp when your house gets to 81? Also, what region? 69 is way below modern day interior temps, so you probably will need to way oversize it. |
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First... What makes you believe your system is undersized? Was a proper heat loss/heat gain survey performed to prove it was undersized or did a tech tell you this? Second... Have you ever had your ducting professionally balanced? Proper airflow calculated and adjusted to the room sizes? Third.... Have you had your system checked to insure it's working at it's peak performance? If so, do you have documentation of superheat, subcooling, delta T, pressures, amps/volts, blower CFM? 1. The HVAC tech that came out to look at why it isn't shutting down or able to cool off the upstairs said it was probably undersized. He said that if everything was perfect it might would work but it would never be able to strip the heat out of the house if we let it get to warm. 2. No we just bought the house. it was built in 2003 so I don't know if it was ever tested. 3. The tech that came out a month ago tested the system pressures and temps at both the unit and the vents.He did a few other things but I have no Idea what it was. He did say that he thought it was slightly over pressured and got that number down to spec. He was unsure about adjusting the blower speed do to not having a manual for our brand and model. If you still have the report from that inspection/repair and can scan it, I would love to see it. If you have access to a simple thermometer we could do some very simple tests to see how your system is acting. |
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I was never given a report. I remember when we were testing that the air just outside of the blower was 63 degrees and within a degree or two of that at the Vents. I have a thermometer what should I check? You want to check the return air temp going into the furnace and then the leaving air temp about 10' down stream of the indoor (evaporator) coil. Look for holes on the duct work near seams and corners to poke the thermostat in. If you could post both temps we would have an idea of how the system is performing. ETA- Drop the setting on the stat 5*F or more and allow the system to run for 5-10min before taking the readings. |
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Quoted: Quoted: Get some shade on that big window, an awning is the most effective thing, lower on the list is some kind of reflective film, but it you can keep the sun from hitting that big window at all, that's the most effective thing. The big window has tinted low e glass. In fact it doesn't feel any hotter next to the window. If sunlight is going through it, the heat load is still high. Awnings are awesome for this. Or deciduous trees. |
| Add a large, high efficiency window unit or two. Only marginally less efficient than your central unit. With a little tinkering with the T' stat on the window units, you can get them to kick on when that level of the house begins to exceed the central units capacity. We used one upstairs just to allow the master suite to be cooled lower than the rest of the house. It lowered our overall electric bill, since we did not refrigerate the downstairs when no one was using it. |
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Ran into this with a custom house in the Napa valley. All windows, floor to ceiling, for the view. Customer decides towards the end of the project that the house is too hot. HVAC guy starts pulling his hair out as he told the owner this while looking at the plans. Fortunately the homeowner has more money than sense. HVAC guy installs largest AC units available. Fortunately the house also has 400 amp service! AC barely able to keep up with cooling even after window tinting. Only option at this point is to close the blinds during the day, which defeats the purpose of the windows, the view. Its a weekend home so its not too bad. I'd hate to pay the power bill though. |
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Have you shut most, maybe all, of the vents in the basement and then open up the ones all the way upstairs to see if that will help before laying out that cash first? I was told by the HVAC technician not to do that. That by closing off the vent it would wreck the efficiency of the system and wouldn't cool as well.  Get a new technician.
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Have you shut most, maybe all, of the vents in the basement and then open up the ones all the way upstairs to see if that will help before laying out that cash first? I was told by the HVAC technician not to do that. That by closing off the vent it would wreck the efficiency of the system and wouldn't cool as well. Get a new technician.I'm no HVAC tech nor engineer, but say he did close all the lower vents, would the vents upstairs be able to flow that volume of air? Or would it just put additional strain on the blower? |
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Have you shut most, maybe all, of the vents in the basement and then open up the ones all the way upstairs to see if that will help before laying out that cash first? I was told by the HVAC technician not to do that. That by closing off the vent it would wreck the efficiency of the system and wouldn't cool as well. Get a new technician.I'm no HVAC tech nor engineer, but say he did close all the lower vents, would the vents upstairs be able to flow that volume of air? Or would it just put additional strain on the blower? At the risk of over-simplifying, the volume of air drawn into the system equals the volume leaving the system. If the area of vents leaving the system is smaller than area coming in, there is a velocity increase at the exit vents until the flows equalize. There is a point where the flow will "choke", but for practical purposes that point won't be reached by closing a few vents. Even in a choked condition, the fan is more or less just spinning without much load on it. The evaporator might ice up in that situation however. |
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Ive got the same problem...we did some rennovations, put in large double doors, bigger windows, and opened the dining room into a porch area.... Then remodeled the basement, and all the duct work had to be moved to accomodate.
We now battle a undersized system and too much static pressure in the hvac. Fucking sucks - set the ac on 69, we get 78 upstairs - single story house. Remodeled basement remains freezing. All ducts in basement are off. The electric heat pump does ok in the winter, but struggles on very cold nights to keep temp. |
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Quoted: I was never given a report. I remember when we were testing that the air just outside of the blower was 63 degrees and within a degree or two of that at the Vents. I have a thermometer what should I check? 63 is too high, IMO... My A/C is a 3 ton unit, not sure of the blower CFM, and the other day on a 92 degree day it was blowing out 51 degree air in the vent furthest from the system with the thermostat set at 76. Two possibilities come to mind... Either you've got too much refrigerant in the system and it's not changing state correctly (liquid doesn't turn to gas as it should), or you're low on refrigerant. Either way, it won't cool. It *could* be the blower isn't putting enough air across the A coil to effectively cool the air, but I've run ours on medium speed year round before and it's worked fine. FWIW, I just took the temp of one of the vents here in the room I'm in (2X12 vent, with about 40 feet of duct line (hard, not the flex stuff)) between it and the unit under the house, and the temp got down to 50.5 degrees in about a minute on the digital thermometer I used to test it. The house is still set at 76. Something is wrong if it's only putting out 63 degree air... Might want to get a set of gauges and learn how to read the pressure in your system. Heck, just buying a set would probably be cheaper than having an HVAC guy come out and check the pressures. Put them on the high and low lines out by the unit and see what happens. You'll need to know what type of refrigerant is in the system as well as the outside temp so you can know what the pressure in the system SHOULD be. The type of refrigerant should be listed on the side of the unit. ETA: House is now around 2000-2050 square feet now thanks to the additional room we just added, but we insulated the heck out of it (2X6 walls with R19 in them, foil-backed bubble-wrap type stuff 1" down from the roof in the vaulted ceiling, and then R30 between it and the drywall for the ceiling). I also have around 14" of insulation in the attic all over the rest of the house now. Hoping to put a radiant heat barrier in the attic up against the rafters at some point next spring. ETA2: Gauges/hose sets: http://www.amazon.com/Yellow-Jacket-41215-Manifold-Gauges/dp/B00159TFSS/ref=sr_1_8?s=hi&ie=UTF8&qid=1372647177&sr=1-8&keywords=manifold+gauge+set+with+hoses $72.50 and you can get the R12 to R134a adapters for another $15 and can test/fill your vehicle as well with them. |
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Here are some temps from the system this morning.
It's about 74 outside. The thermostat was saying it was 78.7 inside. A separate thermometer inside was at 79. The return near the filter was 73-74 and further up it was around 75. After the system was running for 5 minutes. Above the coil about 8" was 61 and 63 at upstairs vents in front of the big window. The vents in the bedroom on the far side of the house are 65. These are the same numbers we got when the tech was out. He never upped the blower motor speed would that help? |
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Quoted: Here are some temps from the system this morning. It's about 74 outside. The thermostat was saying it was 78.7 inside. A separate thermometer inside was at 79. The return near the filter was 73-74 and further up it was around 75. After the system was running for 5 minutes. Above the coil about 8" was 61 and 63 at upstairs vents in front of the big window. The vents in the bedroom on the far side of the house are 65. These are the same numbers we got when the tech was out. He never upped the blower motor speed would that help? Changing the blower speed could help some, yes, but if it's already on medium (or high), then I'd be there's something wrong with the amount of refrigerant you have in it (too much or too little). 61 is just too darn high if the temp for the return is 73-74. Mine is running around a 28 degree temperature drop between the return and the vents. Yours is only 12-13. That's a problem. |
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Here are some temps from the system this morning. It's about 74 outside. The thermostat was saying it was 78.7 inside. A separate thermometer inside was at 79. The return near the filter was 73-74 and further up it was around 75. After the system was running for 5 minutes. Above the coil about 8" was 61 and 63 at upstairs vents in front of the big window. The vents in the bedroom on the far side of the house are 65. These are the same numbers we got when the tech was out. He never upped the blower motor speed would that help? Changing the blower speed could help some, yes, but if it's already on medium (or high), then I'd be there's something wrong with the amount of refrigerant you have in it (too much or too little). 61 is just too darn high if the temp for the return is 73-74. Mine is running around a 28 degree temperature drop between the return and the vents. Yours is only 12-13. That's a problem. I noticed our thermostat has an EER setting that is enabled that wouldn't cause this problem would it? It's a variable speed blower so how do I know if the speed is set correctly? It's wierd because when it's not to hot out it almost feels like the house gets colder without the ac running and just the blower fan which is on all of the time. |
| I am an HVAC tech by trade. The temp drop (delta-T) you have is too low. There is not "perfect" number for this but I have found that if the Superheat, Subcooling and refridgerant levels are in accordance with the manufacturer, as well as the correct blower setting to ensure proper CFM which means proper evaporation, the delta-T tends to in the 19-24 degree range. One thing these armchair HVAC techs arent asking about is the metering device. How old is your system? Does it use R-410A or R-22? It is likely using R-22 with a piston for a metering device. If it's old enough, it may still be using capillary tubes. I can also tell you that the problem is not the blower speed. You want to think that because it is an easy fix but it is not the fix. I have never fixed your problem by adjusting the blower speed. One more thought...it sounds like you hired a company how likes to sell new equipment. Find another company. There is alot more to this issue than refridgerant levels, blower speeds, and open/closed vents. |
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I am an HVAC tech by trade. The temp drop (delta-T) you have is too low. There is not "perfect" number for this but I have found that if the Superheat, Subcooling and refridgerant levels are in accordance with the manufacturer, as well as the correct blower setting to ensure proper CFM which means proper evaporation, the delta-T tends to in the 19-24 degree range. One thing these armchair HVAC techs arent asking about is the metering device. How old is your system? Does it use R-410A or R-22? It is likely using R-22 with a piston for a metering device. If it's old enough, it may still be using capillary tubes. I can also tell you that the problem is not the blower speed. You want to think that because it is an easy fix but it is not the fix. I have never fixed your problem by adjusting the blower speed. One more thought...it sounds like you hired a company how likes to sell new equipment. Find another company. There is alot more to this issue than refridgerant levels, blower speeds, and open/closed vents. The system is an R-22 system. What else can I look for before calling out another tech?I would like to have much information as possible. I have no problems calling them out until we can get it fixed but at $100 a call I need to get this fixed sooner than later. For mow the system is holding the house right around 78-79 degrees but when it hits 90 to 100 the place is going to get way to hot on the main floor. The basement is fine if anything it's too cold. The temp in the basement is 74-72. Could the humidifier be afecting the temps? |
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Ok, so you are getting a 10-12°F temp drop across the coil.
The general rule of thumb for this type of equipment and what the manufactures design it to perform at is 20°F temp drop (delta T, temp differential) So you have something wrong. That little test tells me one of two things... 1) Your blower speed is too fast, pushing air across the coil at velocities where it's unable to transfer heat to the refrigerant. This could be a simple adjustment of the fan speeds or it could be a completely mismatched system where it's a severely over sized furnace or undersized A/C coupled together. 2) Your refrigerant cycle is not working properly. This could be overcharged, undercharged, bad metering device, poor compression, plugged condenser coil, wrong sized fan in the condenser, or a host of other issues. My suggestion.... Find a company that strives to solve issues, not sell equipment. You want a SERVICE tech, not a SALES tech. Get the answer as to why you only have a 10°F temp drop across that coil. Ask to see superheat and subcooling readings then ask what the A/C manufacture recommends for that reading, ask what metering device you have, ask to see volts and amps, ask for a static pressure test to know what CFM your blower is running, and get it all in writing, on a report, signed by the tech. Anything less is just hacks ripping you off. 
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Ok, so you are getting a 10-12°F temp drop across the coil. The general rule of thumb for this type of equipment and what the manufactures design it to perform at is 20°F temp drop (delta T, temp differential) So you have something wrong. That little test tells me one of two things... 1) Your blower speed is too fast, pushing air across the coil at velocities where it's unable to transfer heat to the refrigerant. This could be a simple adjustment of the fan speeds or it could be a completely mismatched system where it's a severely over sized furnace or undersized A/C coupled together. 2) Your refrigerant cycle is not working properly. This could be overcharged, undercharged, bad metering device, poor compression, plugged condenser coil, wrong sized fan in the condenser, or a host of other issues. My suggestion.... Find a company that strives to solve issues, not sell equipment. You want a SERVICE tech, not a SALES tech. Get the answer as to why you only have a 10°F temp drop across that coil. Ask to see superheat and subcooling readings then ask what the A/C manufacture recommends for that reading, ask what metering device you have, ask to see volts and amps, ask for a static pressure test to know what CFM your blower is running, and get it all in writing, on a report, signed by the tech. Anything less is just hacks ripping you off.
This |
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Ok, so you are getting a 10-12°F temp drop across the coil. The general rule of thumb for this type of equipment and what the manufactures design it to perform at is 20°F temp drop (delta T, temp differential) So you have something wrong. That little test tells me one of two things... 1) Your blower speed is too fast, pushing air across the coil at velocities where it's unable to transfer heat to the refrigerant. This could be a simple adjustment of the fan speeds or it could be a completely mismatched system where it's a severely over sized furnace or undersized A/C coupled together. 2) Your refrigerant cycle is not working properly. This could be overcharged, undercharged, bad metering device, poor compression, plugged condenser coil, wrong sized fan in the condenser, or a host of other issues. My suggestion.... Find a company that strives to solve issues, not sell equipment. You want a SERVICE tech, not a SALES tech. Get the answer as to why you only have a 10°F temp drop across that coil. Ask to see superheat and subcooling readings then ask what the A/C manufacture recommends for that reading, ask what metering device you have, ask to see volts and amps, ask for a static pressure test to know what CFM your blower is running, and get it all in writing, on a report, signed by the tech. Anything less is just hacks ripping you off.
Thanks for the help. I just checked down stairs again and its 68 with the upstairs being 78 is a 10 degree differance between floors normal? I think it's going to come back as the furnace being to big for the A/C. But getting a true report will give us something to work from. It pisses me off that my old house that was built in 1920 with shitty ducts and virtually no insulation, hardly any return duct work, and windows that leaked like a sieve cooled and heated like a champ and did it cheaply. This house has all of the bells and whistles and is giving me fits. WTF 
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I want you to read this installation manual for your furnace... Pay close attention to pages 16 and 17.
This is how you properly adjust your airflow... You have a 2.5 ton condenser. You need to make sure your airflow is set for a 2.5 ton system. I am willing to bet you find it set much higher. All you need to do is check the two banks of dip switches. Make sure the power to the furnace has been shut off before checking anything. Manual Here Dip switch settings that you need for your 2.5ton system... #1 up (off) #2 down (on) #3 up (off) #4 down (on) This will get you the needed 1000cfm your cooling requires. Make a note of what the switch setting were before you change them and post them here. I am really wondering if you are moving too much air. After looking through it, I bet it's still set to the factory default setting and you are moving close to 1450cfm which is way too much for your cooling system. |
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Here is the picture of the switches. When comparing it to the manual I have 1,2,3 on and 4 off. That would mean it's set for D+ or 1572CFM. So if I'm reading this right I need to flip 1 and 3 off and 2 and 4 on. If this works I owe you big time. https://lh3.googleusercontent.com/-37AsTq7KxHw/UdJRSZWfAbI/AAAAAAAACmw/YwuswIFcg2o/s640/20130701_214640.jpg Even worse... It's set up for over 1500cfm Set the switches how I have them listed above (on/off) and then retake the temp drop across the return and supply air. I bet you get closer to the 20°F target. |
| Quick update. I made the changes to the blower speed and checked the the temps we are now at 59 at the vents and 75 at the returns from the upstairs. But the unit still isn't cooling off the upstairs. When I turned the system on after making the changes the thermostat read 76.5. I set it for 76 so it would kick on. The system has been running for over an hour and it's 78.5 in the house now at the thermostat. I also notice when I was measuring the temps today that our duct work leaks like a sieve at the take offs from the spiral pipe. The boots were install with big gaps. I spent an hour or so sealing those up with foil tape I'm not sure that it will help. At this point I think out biggest issues is trying to cook a 3400 square foot house with a 2.5 ton ac unit. The window and the vaulted ceilings are going to fight us until we can really push the air around. |
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We just bought this house a few months ago and the AC unit is undersized. The house is well insulated but has a huge window and high ceilings on the main floor. The basement stays cold while the main floor gets hot. Even with the ac kicking on at 10:00 am when it's cool out the unit isn't able to cool off the main floor and runs all day. In fact when it cools off at night we are better off shutting down the system and opening the windows. We have a nice furnace with a variable speed blower so I don't understand why they undersized the AC unit. Is there anything else that we could try? We were quoted around $3000.00 to replace this unit with a 3.5 ton 13 seer that included cleaning and reusing our existing line set. This seems high to me. I thought about putting a ceiling fan in the great room to help push some of the hot air off and increase the cooling but I doubt that will help the AC unit cycle. I am in the exact same boat, OP. I have had 4 different HVAC companies out here and they all say the thing is undersized. I continue to doubt them only because my neighbor has the identical floor plan/square feet, and the same unit (size, model, etc...) and her house gets to 67 if she sets the thermostat to that. We bought the house 3 years ago, built in 2002. Yesterday, I set ours at 69, and it got to 81! Two companies have quoted anywhere from 3-5K for a new unit. I sure as hell don't want to spend that on an AC. Kind of funny, I just dropped 3700 on a new JP LRP-07 I had no qualms doing that, didn't even think twice! You guys know I have my priorities straight at least!When it is running, what is the temp at the return vs the registers closest to the unit? |
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At this point I think out biggest issues is trying to cook a 3400 square foot house with a 2.5 ton ac unit. The window and the vaulted ceilings are going to fight us until we can really push the air around. I'd say your biggest problem is/was the lack of temperature difference between return air and register. However, 3400 sq feet with 2.5 tons? Granted - some of that is basement but that just sounds crazy.... but then I am in Texas and we don't have basements and its regularly over 100. I have 3000sq ft and have two units totaling 6.5 tons. And my AC guy said he'd recommend moving my primary unit up from 4 to 5 tons when I replace it with a dual stage system. |
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Quick update. I made the changes to the blower speed and checked the the temps we are now at 59 at the vents and 75 at the returns from the upstairs. But the unit still isn't cooling off the upstairs. When I turned the system on after making the changes the thermostat read 76.5. I set it for 76 so it would kick on. The system has been running for over an hour and it's 78.5 in the house now at the thermostat. I also notice when I was measuring the temps today that our duct work leaks like a sieve at the take offs from the spiral pipe. The boots were install with big gaps. I spent an hour or so sealing those up with foil tape I'm not sure that it will help. At this point I think out biggest issues is trying to cook a 3400 square foot house with a 2.5 ton ac unit. The window and the vaulted ceilings are going to fight us until we can really push the air around. I would tend to agree that a 2.5 ton system on a 3ksq/ft house is pushing it.... Now that we have airflow dialed in on the cooling try to do a poor mans air balance to help get some of that cool air where you need it the most, upstairs. Read this thread and follow my instructions in the post.... http://www.ar15.com/forums/t_1_5/1491012_HVAC_guys__Upstairs_10_degrees_hotter_and_more_humid_than_downstairs.html |
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I tried to balance the system and it it's still about the same. the thermostat hovers between 78.5 to 78.7. It's good that it's able to hold that but that means the system runs all day. If we kick it off it is not able to recover from the heat gains.
I had a guy from a local HVAC company come out this evening and take a look. He wants to up the condenser to a 4 or 5 ton unit. This creates a cascade of issues including a 3/4" line set and a 30 amp breaker on the current unit. He said the max we could go is a 4ton with our existing line set and that was with them converting it to 7/8 in the areas that were exposed. I'll have to check the wire size tonight to see if they ran 8 gauge over to the condenser. This quote came in at $5000.00 At this point it looks like I'll be getting quotes from all of the local companies and see what we can come up with. I can't wait to see what our electric bill is going to be this month. |
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Have you considered adding a second (small) unit and re-ducting? Wouldn't two units be typical for a three level 3400 sq ft home there? Well so far everyone wants to just swap condensers. It's only a two story house. It's a main floor and a basement. It kills me because the basement gets so damn cold. If I could just get all of that air upstairs I would be golden. |
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I tried to balance the system and it it's still about the same. the thermostat hovers between 78.5 to 78.7. It's good that it's able to hold that but that means the system runs all day. If we kick it off it is not able to recover from the heat gains. I had a guy from a local HVAC company come out this evening and take a look. He wants to up the condenser to a 4 or 5 ton unit. This creates a cascade of issues including a 3/4" line set and a 30 amp breaker on the current unit. He said the max we could go is a 4ton with our existing line set and that was with them converting it to 7/8 in the areas that were exposed. I'll have to check the wire size tonight to see if they ran 8 gauge over to the condenser. This quote came in at $5000.00 At this point it looks like I'll be getting quotes from all of the local companies and see what we can come up with. I can't wait to see what our electric bill is going to be this month. http://www.ar15.com/forums/t_1_139/1492957_So_you_re_replacing_your_HVAC_system_.html |