Does anybody currently have or have had experience with one of these systems?  I was debating installing one in my house but am undecided after reading some articles on them and comparing the pros and cons.  Our house is pretty dry, especially this time of year of course, and we are already running two humidifiers and might need a third for each of the rooms.

I'm in the same boat as you.  Running two humidifiers and it stays around 30% & would like to get to 40%.
Hopefully the experts will come in.  House is over 4,000sf and have two HVAC units.

Meh, house came with one, still use portable humidifiers at times during the year.

I use an Aprilaire 800 steam humidifier.
It’s an older model that can put out 23 gallons a day.
The newer model can do around 30 wired at 240 volt.
It generates the steam using 2 electrodes in a water bath so it’s not cheap to run,but the only humidifier that can keep my 4,000 sf house comfortable.

I should add I’ve tried others.
Skuttle spray humidifier , a bypass and even a Honeywell Trusteam.
Nothing comes close to the 800 regarding output and easy Seasonal maintenance

This is the ONLY appropriate answer.

Installed an Aprilaire 600m wired through my ecobee3 with the hot water line tapped, does well in our 2200sqf home. Or if you have the space on your ducting the Aprilaire 700 would probably do even better. Steam units are supposed to be the best, but they do come at a higher intial cost and running cost.

I have installed more Aprilaire systems than any other.

I have ripped out a lot of furnace mounted whole house humidifiers too, including my AprilAire that I installed 12 years ago (was on the fritz and we didn’t need it anymore).

What was your reasoning for not installing another?

Higher initial cost yes, but lower operating costs and they actually can hit your humidity setpoint vs a bypass style that can't.

Definitely more efficient and yes since it is injecting steam directly into the airflow you will hit your goals. We've been lucky, my bypass setup is doing well enough but we don't really run our humidity up high like some like.

Didnt need it, six people in a 1800SF home generates plenty of humidity.  We also don’t have hardwood floors or fancy furniture.

The bypass duct was a head knocker when doing laundry so that was another reason.

Certain areas could actually use a dehumidifier.

Are these systems hard to install?  I'm no HVAC expert but I know enough to be dangerous

You need to have the ability to do plumbing, HVAC, and electrical.

Is it rocket science?  No.

Just don't burn your house down or flood it.

Not true.  Steam has higher operating costs.  The 800 draws about 16 amps vs a bypass that uses no electricity.

But they do work exponentially better.  Bypass and fan powered humidifiers usually only hold set point in nice tight houses.

That being said, if your house is extremely loose, the 800 won't hold it either.

Don't install it in the 120v configuration, even though it is an option.  If you have a softner, source the water before it gets softened, unless it is extremely hard (above 30 hardness).

25 year HVAC tech here.

Steam has lower operating costs than a bypass.

A bypass flushes 3 - 4 gallons of water down the drain for ever gallon it puts into your air.

A bypass - to help maximize it's inefficient design - needs to be hooked to a hot water line, so your water heater is running.

A bypass - again to help maximize it's inefficient design - needs to have your heat source running, especially if it's a heat pump.

Unless you do those last 2, there is also no way a bypass can humidify your home, therefore it's a waste of money.

And we haven't even talked about the organic growth problems the bypass has...

Speaking of organic growth.  Do any or all of these systems have issues with that type of thing?  In the duct work or the entire house?

Even at 3 gallons of loss per evaporated gallon you would have to know the cost per gallon of DHW vs the electric use of the steam.  Heating water with gas can be 1/3 of heating it with electric depending on where you live.

I would never suggest a bypass unless its output would be sufficient to satisfy set point during the heat calls of the home.  Running a bypass with no heat source running is terribly wasteful because it would have almost no effectiveness.

Steam is not always the right answer.  A proper psychometric calculation figures load and cost (per kWh, per therm, per gallon of water etc).  In a tight home with relatively high electric rates and NG as the heat and DHW source, an evaporative humidifier is still the most efficient choice.  It is the same with hvac equipment in general.  Is a 20 seer AC more efficient than a 14?  Sure.  But figuring energy costs and load may still prove that the 14 seer is the cost effective choice for some situations.

Organic growth is solved with a $6 pad.  You can buy about 15 for the price of one steam canister.

Pretty much any of them but a steam humidifier will grow stuff inside of them and potentially inside your ducts.

I'd have to see if I can dig the info out again, but when Honeywell first released the TrueSteam they had the calculations done for each of the 4 regions of the country, using the utility rates for those areas.  In every area, the steam humidifier had the lowest operating costs.

Sure you can replace the pad, but what about the growth inside the duct work?

About the only instances I have seen where the 14 is more cost effective than the 20 is where the homeowner cannot reasonably afford the 20.