bypass humidifier hooked up correctly?

[Bill in MI]

Living in a new house (to us) and getting things squared away, one by one.

Had to replace a defunct humidifier. After installing it where the old one was (and closing up slightly smaller hole), it dawned on me that it is mounted to the return duct rather than the supply duct which I thought was the "correct" way. But after finding this: reversed bypass duct installation, it seems that my installation is acceptable?

In the pictures below, you can see the humidifier is on the return duct, and the bypass duct comes off of the supply duct. Presumably this was done because there's not room to do the install the typical way.

Thoughts on this?

Also looking for thoughts on humidistat placement. Thanks.

 

[larry4406]

A bypass type uses higher pressure supply air to blow across the wetted membrane to the low pressure return side. No extra fan needed. Make sure humidistat is upstream of the entrance to the cold air return. These benefit from hot water supply.

I think looks ok. Note the black handle. It has on/off positions for summer/winter

 

[Bill in MI]

Great, Larry, thanks for the confirmation. One less think for me to worry about.
-Bill

 

[brewchief]

Bypass mounted on return is fine, I prefer to do it that way if possible, that way if it doesn't get serviced and ends up leaking water and doing damage it's a rusty return drop instead of a rusty furnace.

Which controller do you have? Manual or automatic? It should be upstream of the humidifier, the location of the old one isn't terrific but it will work ok there, ideally it would be a bit further upstream.

Hot water is preferred but it will work ok on cold.

I'm not a fan of the drain tube like that, we use 3/4" pvc for all of our drains.

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[Bill in MI]

Which controller do you have? Manual or automatic? It should be upstream of the humidifier, the location of the old one isn't terrific but it will work ok there, ideally it would be a bit further upstream.

Temporarily using the old automatic controller. (Been sick all week). In the next couple of days I'll switch to the new automatic controller that came with the unit. I can cover up the old hole and cut a new one further up when I change it out if you think that would help.

Hot water is preferred but it will work ok on cold.

Hot water is hooked up to humidifier.

I'm not a fan of the drain tube like that, we use 3/4" pvc for all of our drains.

I was stuck using a flexible tube because the humidifier has a funky fitting that doesn't permit a PVC connection.

Thanks for the input.

 

[brewchief]

Temporarily using the old automatic controller. (Been sick all week). In the next couple of days I'll switch to the new automatic controller that came with the unit. I can cover up the old hole and cut a new one further up when I change it out if you think that would help.



Hot water is hooked up to humidifier.



I was stuck using a flexible tube because the humidifier has a funky fitting that doesn't permit a PVC connection.



Thanks for the input.

You can simply slide 3/4" pvc over the fitting on the bottom , alternatively a short piece of flex tube draining into the pvc works ok, I have seen to many small drains plug up over the years. I'll see if I have a pic, I've installed hundreds of these over the years.

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[brewchief]

Lennox humidifiers here but uses the same drain fitting as the aprilaire.

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[Climatecreator]

You don't WANT the humidifier on the return side because it puts damp air into the heat exchanger etc. More than what would be after it goes up the supply then returns naturally. Also there's the fact that the hot heat exchanger cooks the humidity out of the air. That you just put into it....

Supply side mounting is best with hot water supply. Period

CC

 

[brewchief]

You don't WANT the humidifier on the return side because it puts damp air into the heat exchanger etc. More than what would be after it goes up the supply then returns naturally. Also there's the fact that the hot heat exchanger cooks the humidity out of the air. That you just put into it....

Supply side mounting is best with hot water supply. Period

CC

A bypass humidifier will always have airflow from the supply to the return, it doesn't matter where it's mounted. In over 20 years I have removed hundreds of furnaces with humidifiers and I have never seen one with damage from a probably maintained humidifier, I have seen damage from plugged water panels and drains.

If you don't want the humidified air to pass through the furnace then a fan powered unit is an option or a steam unit if you need lot of moisture and don't mind using a bunch of electricity to get it.

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[The Cobbler]

heated air picks up more humidity that cooler air, so it is actually more efficient to send heated air through the humidifier . normal install in my opinion

 

[larry4406]

You don't WANT the humidifier on the return side because it puts damp air into the heat exchanger etc. More than what would be after it goes up the supply then returns naturally. Also there's the fact that the hot heat exchanger cooks the humidity out of the air. That you just put into it....

Supply side mounting is best with hot water supply. Period

CC

Supply side mounting won't work with the unit the OP has as it does not have fan assist to blow into the higher pressure supply side.

 

[hockale1]

necro-thread incoming...reading into supply vs. return bypass humidifier installation i'm finding the discussions tend to resemble that of pre-twist vs. straight wire nutting.

Nevertheless, AprilAire addresses this in the install manual so i thought i would share. OP's bypass humidifier install pamphlet follows the same convention as mine, and it does make a point to say either installation is acceptable.



I do find it funny/confusing how the pictographs for horizontal and upflow system install both feature supply-side configuration

maybe they're trying to insinuate something

---

My thoughts? It depends entirely on fluid dynamic properties which are likely significantly (enough) influenced by the exact dimensions of any given forced-air installation, even between the same furnace unit installed in two different dwellings...

Generally speaking, it does appear to me in favor of supply side pad placement; air flow across a bypass duct installed on the return plenum, according to prof. bernoulli's rules, will result in a local low pressure condition at the duct orifice encouraging some flow directionally into the supply (--> fan --> furnace) from the bypass duct. Admittedly this flow is possibly miniscule, but the science says there should be some.

On the other end of this installation, there will be an overwhelmingly positive pressure at the humidifier pad, complementing the low pressure duct orifice condition, and giving an overall system behavior of supply air flow across the pad, through bypass ducting, and into the supply plenum. I would expect the pad to provide more pressure drop than air simply going onwards to heat registers so as not to get into some infinite humidifcation flow loop.

If you flip the configuration around, you won't be able to leverage the same system harmonics as provided by a supply side installation. High pressure and high air velocity vs a relatively low pressure at a bypass duct on supply side should provide some backflow into the duct, but i don't get the impression that return side flow will be high enough to siphon air through the pad and into the furnace....

that's my ~10 years out of mechanical engineering school take on the topic. i've spent more of my night thinking on this than i wanted to..

 

[fitter30]

You don't WANT the humidifier on the return side because it puts damp air into the heat exchanger etc. More than what would be after it goes up the supply then returns naturally. Also there's the fact that the hot heat exchanger cooks the humidity out of the air. That you just put into it....

Supply side mounting is best with hot water supply. Period

CC

Bypass it doesn't matter which side it's on rh is going through the return