Humidifier Bypass Duct Placement Help Needed

Thanks Scup for the info. as well as clearing some things up. Ray

LLigetfa said:

Modern well sealed homes already factor for that by providing a HRV. In modern homes, the appliances often have their own dedicated make-up air vent. By code in most places, a general make-up air vent is required to be run to the cold return duct.

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Did you mean such a vent is required, or are you saying that if you have such a vent, it is required to run to the cold air duct?

Michigan Ray said:

Not to argue, but I guess everything I have read from the pro's is wrong..... go figure. Not to mention my own experiance with/without humidification. Everyone is entitled to their own opinion. I just disagree with yours.

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My opinion is clearly being overly influenced by my engineering profession, and physics & math degrees. I "believe" in the building science, well supported by the data, and accepted into building codes. I'm a by-the-numbers sort of guy- L'aritmetica non è un opinione, as the Italian expression goes, my best interpretation is- "the arithmetic is not an opinion." There are very few building scientists wasting their careers in the HVAC biz, and I can count on one hand the number of HVAC "pros" I've dealt with who understand much it in any depth. YMMV.

Winterime outdoor dew point averages in the upper midwest of the US are not drastically lower than New England, and are higher than in the Canadian midwest, where dry conditioned-space air in winter is still a symptom an overventilation problem. Houses don't need to be anywhere near PassiveHouse-tight ( 0.6 air exchanges per hour at 50 pascals pressure) or R2000 tight (1.5ACH/50) to need active dehumidification to keep the indoor RH under 35%. Code-max air leakage for new construction in MI under IRC 2012 would be 3 ACH/50, and even that would be more than tight enough. My house isn't that tight yet.)

Go ahead and actively humidify- it's your choice, but take heed- do not exceed 35% RH @ 70F to avoid the excess moisture accumulation in susceptible materials along the exfiltration paths. There is some risk to opting for the band-aid rather than fixing the problem at the source.

And that has NOTHING to do with whether your house was built with vapor barriers or not. In a house leaky enough to require active humidification to get the the air-leakage is moving at least 100x more moisture than vapor-diffusion through a latex-painted wall with no vapor barrier. In fact, in a house that leaky a vapor barrier would aggravate the problem, since it would slow the drying the accumulated moisture in the shoulder-seasons, when the air-handler driven leakage that might improve drying rates along those exfiltration paths falls off with heating load.

The health and comfort range for humans is between 30%-50% RH. The healthiest range for houses built with wood sheathing is 15-20%, but without air-leakage from the interior the risk of mold & rot is quite low in US climate zones 5A & 6A, which covers all of MI except parts of the U.P..

Reach4 said:

Did you mean such a vent is required, or are you saying that if you have such a vent, it is required to run to the cold air duct?

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I am not a code expert for your area but it was a code requirement here when I built my house. I have a 6 inch duct from outside, going through my HRV and terminating near the furnace on the cold return. This is an always open path for outside air that is both pushed by the HRV fan and pulled by the furnace blower.

In the OP's case, I am going to guess that he is probably losing more indoor air to the outside than what is required for minimum ACH.

I am a firm advocate for leaving the make-up vent open and controlling the loss of air instead.

My HRV has four possible modes of operation. One is a constant low speed with high speed on crank timer. The second is constant medium speed with high speed on crank timer. The third is no speed except high speed on crank timer. The fourth is constant high speed which I never use. Sometimes I will crank the timers repeatedly to increase the runtime.

I choose the mode based on the humidity. In the coldest/dry part of Winter, it is off to preserve some humidity and only cranked to high when cooking/showering.

HRV = Heat Recovery Ventilator. IOW, an engineered air leak that tries to pass heat energy to the opposing stream of air so you don't have to condition it again. This is more than just a duct to the outside. Some can pass both heat and humidity between the two airstreams, some just pass the heat. With no recommendation implied, here is an example https://www.acwholesalers.com/Goodm...20V/39190.ac?gclid=CMai-r6T_LsCFQbl7Aodri0Afw

I think what he meant with NPP = Non-point Pollution.

jadnashua said:

I think what he meant with NPP = Non-point Pollution.

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NPP = Neutral Pressure Plane

I spelled it out on first use so not sure why it would be ambiguous.

http://www.buildingscience.com/documents/digests/bsd-014-air-flow-control-in-buildings
http://homeenergypros.lbl.gov/forum...sure-planes-npp?id=6069565:Topic:81443&page=1

Scup said:

I am not sure why you took such an obvious offense at my post but if it makes you happy then be my guest!

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I have no idea how you inferred that I took offense. Not at all. I simply responded to what you wrote.

jadnashua said:

Some can pass both heat and humidity between the two airstreams...

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I think they call those an ERV. I always look at those with suspicion. If VOCs are condensed on the transfer belt/drum, could they not return back into the home when it evaporates?

Hey guys, nice info, but................ Make a "new" post, this has nothing to do with my original post. Maybe others would be interested. Your info falling under "Humidifier Bypass Duct Placement Help Needed" has nothing to do with the subject line. Thanks, Ray