2 furnaces. Do I need 2 humidifiers?

[njbillt]

I have 2 identical gas furnaces, one for each floor, and now I want to add the humidifier. I'm trying to not buy 2 units. I am considering AprilAire 600 or 700 series, either of which would be of enough capacity for the whole house. My question is, which floor would it be best installed on? All bedrooms are on the second floor, so I set back the first floor at night, and the second floor during the day. All rooms have their own returns, and the house is open to both floors in 2 large areas so air can migrate throughout the house. Any advice is appreciated.

[beenthere]

First floor.

Heated air rises.

[genduct]

Are you sure you NEED 2 units?
Isn't there part of a closet or a place you can build a "bump out" that could accommodate a duct riser to the 2nd floor (attic I guess)?
@ zone dampers could do the same thing, or maybe at that point the East Bdms could be separated from the West. Add 2 stage cooling and you have a more efficient system

[genduct]

PS Vapor Pressure even more so than temp diff will move quickly through the home in an attempt to equalize. I doesn't matter which one you use. The basement choice is probably best because I assume the 2 floor unit is in the attic.

[njbillt]

PS Vapor Pressure even more so than temp diff will move quickly through the home in an attempt to equalize. I doesn't matter which one you use. The basement choice is probably best because I assume the 2 floor unit is in the attic.

Actually both units are in the basement. The 2nd floor ducts go all the way to the attic and distribute from there. Big insulated ducts, no problem there, although I did wonder about condensation.

[njbillt]

First floor.

Heated air rises.

I was leaning towards this for 2 reasons. The 2nd floor ducts, although insulated, go to the unheated attic and I worried about condensation. The other reason is, I supplement with wood heat on the first floor and run the first floor fan to move the heat around. I would want to humidify while doing this, which brings a new question. Of the 2 AprilAire I am considering, one is powered, the other bypass. I don't mind bringing hot water to the unit, but I am not interested in a steam unit. So between the bypass or powered units, which would be better?

[t527ed]

bypass, hot water, 1st floor unit.

[njbillt]

bypass, hot water, 1st floor unit.

I was leaning towards a powered humidifier. Why do you prefer a bypass in my situation?

[genduct]

Where does the combustion air come from for your wood stove? A lot of CA will certainly increase the need for RH
Why 2 units in the Bstm? With a supplementary source of heat, seems like you should 'marry" the return so that the benefit of that could also extend to the 2nd floor.

[t527ed]

I was leaning towards a powered humidifier. Why do you prefer a bypass in my situation?

just don't like the power humidifiers if not required due to duct layout. more parts to go bad and not as easy to service as a bypass.

[beenthere]

If the combustion air for the wood stove comes from inside the house. there isn't a bypass or powered residential humidifier made big enough.

A bypass unit can be installed on the return. And still get the full benefit of the furnace when it runs to add a greater amount of moisture to the air.

[njbillt]

Where does the combustion air come from for your wood stove? A lot of CA will certainly increase the need for RH
Why 2 units in the Bstm? With a supplementary source of heat, seems like you should 'marry" the return so that the benefit of that could also extend to the 2nd floor.

The combustion air for the wood stove comes from within the house. I only use it when it's really cold. Once I get it going, I can damp it down and it glows like a nuke plant for hours.

The house was built in the '80s with 2 oil fired furnaces which were way over sized. When I was able to hook up to nat gas service 2 years ago, I replaced them with 2, 95% 2 stage variable speed gas furnaces. I know I could have used one and mechanical dampers to keep the 2 zones, but it was easy, and I like having backup. Either one of the AC or furnaces would do the whole house in a pinch. So far, 2 summers on the AC and 1 winter on the gas furnaces and I am delighted with my bills. If I have any regret, it's that I didn't downsize the AC units half a ton and go with 2 stage there too, but I have a lot of heat gain in the afternoon. It's dehumidifying well so maybe I'm not so over sized after all. Anyway, one winter on the bucket brigade to the stand alone humidifier was enough. I am ready for a whole house humidifier. STILL leaning towards the AprilAire powered unit with hot water so I can run the fan and humidify when the wood stove is running. My thermostats are connected to my home automation system via RS232 comm, so I can run events to control the blower.

[njbillt]

If the combustion air for the wood stove comes from inside the house. there isn't a bypass or powered residential humidifier made big enough.

A bypass unit can be installed on the return. And still get the full benefit of the furnace when it runs to add a greater amount of moisture to the air.

The house must be pretty tight because the 12 gallon per day Sears stand alone did the job, but it was a lot of work.