Winter dryness (Low Interior RH)
Heating system: Weil McClain Ultra Series 2, hydronic baseboard plus radiant heat (Watts ONIX tubing) in about 25% of heated area. Energy Recovery Ventilator – A/S Trane FreshEffects running usually no more than 10% of the time. A/C – two units – one in tempered basement/crawl space, one in untempered attic. Problem: Interior RH often drops into the mid-teens (14-18%) causing unacceptable levels of interior woodwork shrinkage (especially in several specific areas). Is it possible/advisable to add a humidifier to the basement A/C air handler (no forced air heating, remember) without having to add a heating coil as well? We would have to have a humidistat control not only the humidifier but the fan as well, since there is no call for forced air heat. Or, would the lack of a heating coil cause problems/discomfort/condensation potentially blowing cold air around? This would only be possible for now on the unit in the tempered space since the untempered attic unit (unused off-season) is exposed to freezing temperatures. Thoughts? Jeff
Replies
I'd be concerned about
I'd be concerned about condensation in the ductwork.
One way to raise the RH would be to seal the house ... it would be more energy efficient, too. That's not the answer you were looking for, but the perspective is important.
'Modern' houses tend to leak a lot less and therefore high RH is often a problem to the point you have to ventilate.
Maybe use your exhaust fans a lot less. After taking a shower, leave the bath door open. Use the range hood less. Take up hobbies like aquariums and/or indoor plants.
A humidifier will take a fair amount of energy itself. The heat of vaporization comes to mind.
Your low RH is a hint that there is ALSO an energy thing that may be worth your efforts, time, and/or money.
Vent your dryer inside during the winter.
The issue of low interior humidity in winter comes up often, so most of the oft-repeated replies still apply. Clewless1 addresses most of it. I would add only that very low humidity usually indicates too much air leakage through the conditioned envelope. Dry exterior leaks in only if the corresponding amount of inside air is leaking out somewhere else. If you add humidity to the inside air for comfort, you will be increasing the amount of moisture going out through the exterior envelope, increasing the risk of condensation within the walls and the possibility of rot and mold.
No blower door data but all-new construction (mostly). 2.5" + of R-7/inch closed cell foam in outside walls. Mostly Marvin windows and doors (low E, gaskets, etc.).
The attic is 'flow-thru' ventilated with gable vents at each end - maybe considering the low humidity we should consider blocking the gable end vents in the winter? (while monitoring for any condensation)
We currently have NO condensation issues anywhere, even on a few single-pane openings remaining that don't have storm panels yet.
Junkhound is right, have him build you an RH-sensing air flapper valve that mixes dryer output with interior air when needed.
>>Vent your dryer inside during the winter.
Which will lead to high humidity, likely condensation, maybe mold and maybe even rot in that area....
Remember, there's noting in the house circulating the air in the winter....
You can add a humidifier so long as you supply it with hot water or use one with some sort of built-in heater. Several Aprilaire models can be rigged this way. (Be sure to check any unit you get to assure that it's rated for hot water, and insulate the hot water line feeding the unit.)
You may have to get creative with the controls. On our furnace (where I wanted the humidifier to run when the furnace wasn't heating) I had to add an extra relay to turn on the fan.
Looks like we're probably
Looks like we're probably going to consider the Honeywell True Steam unit and VisionPro IAQ stat
I agree with the sealing leaks approach. It's a win-win.
The goal is to let less cold, dry air inflitrate which saves energy costs and preserves the moisture that is already in the house.
Pumping water into the interior air just masks the real problem.
Honestly I think we're going
Honestly I think we're going to have to do both - it's not a very leaky house.