Recycled Drier Air - Potential Moisture Problems?

Forever_Student

I live in a predominantly cold and dry place: Colorado. We run our gas furnace heat pretty much October - April (~ 7 months) and the AC is only on June - Aug (about 3 months).

We also have an electric dryer in the basement, right next to the furnace, with a 20-30' duct run to dump the hot air outside. Hot indoor air has to be replaced with outdoor air.

I'm considering installing a Duct Diverter Valve like the one below in the line.

Duct Diverter Valves - Automatic & Manual Duct Diverters | US Duct (us-duct.com)

In the winter, I would dump the hot air into the furnace's return line. (I could easily build a filter frame and place a low-restriction, low-quality air filter to capture the lint before it gets to the main HVAC filter.) This would recycle that hot air by sending it through the house. It would offer three bonuses: 1 - "Free" heat that would otherwise be piped outside. 2 - Not dumping air outside means not pulling in cold (often <0F) outdoor air. 3 - A little free humidity added to an otherwise very dry house.

In the summer, I'd still pipe it outside because that hot air is undesirable.

My biggest concern is all that moisture.

Would dumping that much moisture through an air filter and into the return line cause sweating (then mold) on either of the air filters? Or in the duct? Would it cause problems with the fan?

Would the dryer be dumping enough heat to dry the filter(s) and the duct, after they get moist, at the end of its cycle?

Is there a sensor or an easy way to tell the HVAC fan to run anytime it detects high humidity in that return duct or any time the dryer runs? (I'm thinking running the HVAC fan would cause dry cold house air to mix with the hot humid dryer air to keep the moisture down…)

Note, I'd never try this somewhere humid, like the east coast, but for dry alpine environments, I feel like it just might work...

Jamie Hall

You will have a moisture problem. And, without a good filter (not a cheap one) and cleaning it after every single use, you will have a lint and dust problem for the moisture to settle in and grow lovely mold.

Better Idea, if a bit redneck special. Place that 30 foot drier duct inside a bigger 30 foot duct with a fan on it, and put an outside air intake on one end of it and the fan on the other, and discharge the fan near the drier. Poor man's heat recovery ventilator…

Forever_Student

There are a large number of "indoor dryer vent" kits on amazon. Do these work out alright without a moisture problem because they are dumping humid air into an entire room and hundreds of cubic feet of air to mix with? As opposed to my thought of dumping into the return duct with only a couple dozen cubic feet.

Would it work out alright if I drilled a small hole ( ~1" dia) in the return ducting to pull some small amount of air from the room to help reduce moisture in the room? Would that cause a backdraft issue with the gas water heater? I would assume not because if a small hole drawing return air from the room would cause a backdraft issue, then the dryer pulling a LOT of air from the room and pushing it outside definitely would cause an even worse backdraft issue…right?

mattmia2

Just because they sell them, especially on amazon where there is little recourse to go after the seller for damages beyond the cost of the product, doesn't mean it is a good idea. Unless your house is very tight, in CO I would be far more concerned about the lint than the moisture.

If you really want to avoid venting air outside, get a condensing dryer.

Waher

you don’t want lint, moisture, and off gassing laundry detergent type products mixing with your indoor air.