Does anyone know where the air enters an electric clothes dryer?  I am wondering if the air to dry the clothes can be ducted to the clothes dryer so the dryer will not use conditioned air from a very tight home.  Does the air enter from the bottom of the machine or back?  Is there any way to connect a duct to the dryer like furnishing combustion air to a fireplace.

I believe on some models the intake air is from the bottom, but others take it from the back. Appliance cabinets aren't designed to be air-tight and some have panels that are held in place with clips rather than screws (hinged tops, etc) further complicating air sealing. It may be easier to air-seal the room and install a supply air vent to the room. But it really depends on the model.

Dana1,

Thanks.

Alton; you could use a weighted balancing damper on a small duct to draw air is as needed

use a weighted balancing damper on a small duct

That makes sense to me. Open up the dryer and place the small duct near the dryer's internal intake. And close off the room (or perhaps an equivalent cabinet or closet). Consider having the intake absorb heat from the vent (like a HRV). Perhaps tube in tube.

Okay, but during winter aren't you going to be using more energy to heat up colder air?

If we really wanted to save energy wouldn't we go back to the tried and true drying method of our foremothers; on a line, outside? When you go north, to Canada, you see much more outside clothes drying activity than you do in the lower 48. I don't think energy is that much more expensive up there, it just seems to be a cultural thing.

Drying clothes outside in winter only works where it stays mostly above freezing, eh?

Drying clothes outside in summer is problematic in high-humidity climates with dew points north of 70F introducing mold & fungus spores to the clothes.

Using high-speed spin cycle on the washer reduces dryer energy use substantially. Using dryer models that sense humidity is also a big energy winner.

The amount of space-heating/cooling load due to taking in outdoor air is miniscule compared to the heating energy of the dryer in the first place. A primary reason for a dedicated air supply would be to mitigate backdrafting issues on combustion appliances, fireplaces, exhaust vents, etc.

Drying clothes outside in winter only works where it stays mostly above freezing, eh?

Winter is a good time to use the dryer. You get nice toasty clothes, as well. :-)

introducing mold & fungus spores to the clothes.

Yuk.

I've tried several times to find out what volume of air is exhausted by a dryer, but haven't really had any luck.

Drying clothes outside in winter only works where it stays mostly above freezing, eh?

No, they still dry.

In Reviving this thread I was thinking the same thing. The information I was able to obtain said a dryer exhausts 120 cfm.
Given a 2400 square foot home, with 8 foot ceilings, that looks to be .38 ACH for the dryer alone.  In a tight home that is going to build a fair amount of negative sressure?

Posted By whirnot on 21 Sep 2012 09:08 PM
In Reviving this thread I was thinking the same thing. The information I was able to obtain said a dryer exhausts 120 cfm.
Given a 2400 square foot home, with 8 foot ceilings, that looks to be .38 ACH for the dryer alone.  In a tight home that is going to build a fair amount of negative sressure?

The Europeans have long ago engineered an energy efficient product that allows for a dryer to be ductless and utilizes heat pump technology. The top 10 available models in Europe are all ventless. Here in the USA where energy conservation is still behind European and Japanese standards, they don't make an energy efficient heat pump dryer. Supposedly U.S. based Whirlpool is dabbling in the idea but I don't think they made one as of yet.

LBN Labs - Dryer Heat Pump Study

DOE Article on dryers

Right now due to lack of ductless heat pump dryers made in the USA, you will pay $$$ the price for buying one. According to the study, the cost is almost double and it will take 20+ years to get an energy ROI. So I wouldn't buy a heat pump air dryer to save money. If you buy one buy it because you want a ductless dryer. Hopefully the prices will come down and then the ROI will make sense.

Your other option is to buy a ductless condensing dryer. Not as energy efficient but still ductless.

I have subsequently found some data on the amount of air that clothes dryers exhaust and it runs from 125 - 240 cfm.

I ended up dropping my exhaust into the mechanical rooms where it runs about 10 feet through uninsulated metal duct before exiting the building. I guess some heat is reclaimed that way. I also insulated the laundry room and sealed the door, so a window could be opened to provide the makeup air without drawing it out of the house.

Posted By ICFHybrid on 22 Sep 2012 10:55 PM
I have subsequently found some data on the amount of air that clothes dryers exhaust and it runs from 125 - 240 cfm.

I ended up dropping my exhaust into the mechanical rooms where it runs about 10 feet through uninsulated metal duct before exiting the building. I guess some heat is reclaimed that way. I also insulated the laundry room and sealed the door, so a window could be opened to provide the makeup air without drawing it out of the house.

What do you think of ductless dryers?

Sexy idea. Nice toys. Probably make for some great service calls here in the States.

It's unlikely that they could be too easily mainstreamed because of the cost.

Posted By ICFHybrid on 23 Sep 2012 09:05 AM
Sexy idea. Nice toys. Probably make for some great service calls here in the States.

It's unlikely that they could be too easily mainstreamed because of the cost.

Actually they are not that much higher, about $900. Often used incondos and apartment retrofts to save having to have ducts. But the energy use is quite a but higher, and they take a long time to dry a load. Panasonic and others have a number of the HP dryers in europe, hopefully they will offer them here soon. They use about 60% of the energy of a standard model. Energy star has already written standards for them, in anticipation of their arrival.

For $250 I can hang wet clothes in a closet and stick a dehumidifier in there.

I dry clothes on the line all winter, especially on breezy sunny days. They dry to some degree, so at least it cuts down on dryer time, though sometimes it is hard to get the frozen clothes off the line :o) I also have a large wooden rack to dry them inside, but they add too much humidity. I didn't think about putting my dehumidifier in the utility room whilst they were drying - thanks for the tip Jonr!

-Rosalinda

I'd be interesting in knowing how long it takes. Adding a fan would probably help too.

Actually they are not that much higher, about $900.

It doesn't take much to put them far, far out of the regular dryer market.

Last week here in AZ one of the schools fresh air vent/ERV turned off and nobody knew about it until a few hours later. The students and staff began to complain of headaches and not feeling well. The school was evacuated and the FD came in to investigate. They concluded a very high CARBON DIOXIDE reading and opened the doors to let in fresh air and found the ERV was turned off. They turned it back on, checked the CD levels, and let everyone back in to the school.

Just goes to show that in a tight building if you have a lot of people and the ERV/HRV fails, people can suffer from carbon dioxide poisoning. Over time high levels of carbon dioxide can actually kill you but there should be plenty of warning before then. In a school with a high volume of people, carbon dioxide poisoning will set in a lot faster than inside of a home.