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Clothes dryer preheater?

I found that patents exist for products that would use the outgoing heat from a dryer to preheat the incoming air, but I haven't found any thing forsale. I'm not going to get away from using my dryer in the winter, but I'd like to do it as efficiently as possibly. Taking warm air from the laundry room, heating it, and then sending it outside, only to have make up air come from the cold outside seems horribly inefficient. My house is much too humid during the winter to use a dryer diverter and the smell is terrible, so that's not going to work. Nor is simply hanging the clothes to dry, again due to the humidity and the fact that doing that with even a few of my wife's blouses takes days to dry.

So, does anyone know of any available products to reclaim dryer heat?

Link to the patents http://www.google.com/patents/US4063590

Asked by Calum Wilde
Posted Jul 30, 2014 4:48 PM ET


16 Answers

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A pipe-within-a-pipe system to try to reclaim heat from a dryer exhaust duct increases condensation on the duct wall, thereby increasing lint accumulation. The duct clogs up faster, and the fire risk increases. The value of the recovered heat isn't worth these major drawbacks.

Answered by Martin Holladay
Posted Jul 30, 2014 4:57 PM ET



Look into a condensing dryer that doesn't push any air outside.

Answered by Kevin Dickson, MSME
Posted Jul 30, 2014 7:29 PM ET


You may have to move to Europe where heat pump and other vent less condensing dryers are prevalent, almost ubiquitous. In Switzerland it is no longer legal to sell any dryer that does not include a heat pump condenser. After all heat pump condenser dryers use less than HALF the energy to dry a given load of laundry and don't exhaust conditioned air from the building which must be replaced by outside air that must be conditioned at additional energy cost.. If you choose to remain in the US, Canada or Mexico you are hostage to the powerful interests that are antagonistic to energy efficiency and have excluded heat pump clothes dryers from our market . In January of 2014 LG announced a breakthrough model , the DLHX 4072V, that was billed as the first heat pump clothes dryer to be available in North America . It is NOT available and appears to have been canceled!

Answered by Jerry Liebler
Posted Jul 30, 2014 10:18 PM ET
Edited Jul 30, 2014 10:20 PM ET.


AEG sell condensing dryers in Canada - I would guess in the U.S. as well. I'm not sure about "perfekt in form und funktion" but the one I saw yesterday looked well made.


Answered by Graham Fisher
Posted Jul 31, 2014 12:46 AM ET
Edited Jul 31, 2014 12:49 AM ET.


For more information on this topic, see Alternatives to Clothes Dryers.

Answered by Martin Holladay
Posted Jul 31, 2014 4:06 AM ET


Kevin & Graham,

Thanks for the suggestions. But everything I've read on condensing driers says they use more energy than venting driers. They don't reclaim the heat, they just dump it somewhere else. Not to mention it would put more water into my septic tank.


I think you're right... Damn. Thanks for the lesson though.


Thanks for the link, and the well written article. You've given me some things to think about.

Answered by Calum Wilde
Posted Jul 31, 2014 7:14 AM ET



Do you have a reference for the LG heat pump dryer being canceled? I did some poking around and don't see evidence of that. Just that it's not yet available for sale. I also found some material on LG's site that indicates that the dryer does have supplemental heat (electric resistance) but depending on the mode it uses the supplemental heat to greater or lesser extent. I surmise that you could put it in a mode where it used little or no supplemental heat, but the material online wasn't clear about that.

Answered by Joshua van Tol
Posted Jul 31, 2014 8:58 AM ET


All I have is my recollection of a phone conversation with an LG sales manager. There was a similar situation a few years ago. GE announced they were "going to develop a heat pump dryer" and accepted $10 million of stimulus from the US government. Three years later I finally found a GE employee who admitted the program was cancelled. I have no information about the $10 million.

Answered by Jerry Liebler
Posted Jul 31, 2014 10:01 AM ET


There may be a break in the logjam! http://money.cnn.com/news/newsfeeds/articles/prnewswire/DE72235.htm

Answered by Jerry Liebler
Posted Jul 31, 2014 12:21 PM ET


Hi Calum,

Where have you read that heat pump clothes dryers use more power than conventional dryers?

A quick search turned up the following from the state government of Victoria, in Australia:

These clothes dryers use a heat pump to produce hot air, and operate similarly to reverse-cycle air conditioners when heating. These machines are highly efficient, as they condense moisture from being expelled and recover heat to dry the load. Heat pump dryers use less than half the energy of conventional electric clothes dryers, and are worth considering if you use an electric dryer frequently.


The issue of water from a heat pump clothes dryer overloading your septic system seems like a non-issue. The quantities of water that would be extracted from your clothes is so small compared to so many other sources of drain water in your home, including running the washing machine, that it's hard to imagine worrying about.

Answered by Graham Fisher
Posted Jul 31, 2014 1:42 PM ET


Read Calum's post again. Calum was writing about condensing clothes dryers, not heat pump clothes dryers.

Answered by Martin Holladay
Posted Jul 31, 2014 2:01 PM ET


In various experiments over time I've found that dryers actually
don't produce all that much *heat* while they're still removing
the bulk of the moisture. It's just soggy wet somewhat-lukewarm
air until the clothes start approaching fully dry, after which
things get quite a bit hotter. Latent load and sensible heat
ratio and all, y'know.

So when I'm drying in the winter I manually intervene and run it
in two phases: the first with the vent tossed outside through a
basement window with a specially-built blockoff temporarily
inserted, and then when there's almost no moisture left pull
the hose back in and let it exhaust inside to reclaim the
remaining heat without putting any appreciable extra moisture
into the place. I try to make the path of cold makeup air as
short as possible by taking the cover off the shut-down HRV that's
near the dryer and letting that be the cold air inlet. It's not
actually using the HRV in any fashion [whose doc actually says
"do not run laundry exhaust through this!"], just using its
inlet duct as the leak from the outdoors for a while.

Smart dryers that only exist on the ice planet Mongo handle this
by having two vent outputs, one outside and one inside, with an
exhaust gate flap and a humidity sensor.


Answered by Hobbit _
Posted Jul 31, 2014 2:16 PM ET


The inhabitants of the planet Mongo sound technologically sophisticated and very energy-conscious.

You, however, appear to live on the planet Bongo. Inhabitants of the planet Bongo have plenty of free time, and spend their winter hours in the basement, watching their clothes dryers very carefully.

Answered by Martin Holladay
Posted Jul 31, 2014 2:28 PM ET
Edited Jul 31, 2014 2:29 PM ET.


Graham, as Martin said I was referring to condensing dryers, not heat pumps. The idea of a heat pump dryer seems like a stellar idea to me.

My only question about such devices is, when will someone introduce a whole home heat pump. A single compressor running the heat, AC, dryer, water heater, and fridge?

Answered by Calum Wilde
Posted Jul 31, 2014 2:28 PM ET


Does anyone know if a heat pump dryer can dump the condensate into the same pipe as the washer empties into?
For that matter, can a heat pump water heater use the same pipe for condensate?

Answered by stephen sheehy
Posted Jul 31, 2014 2:30 PM ET


Your suggestion of a "home heat pump", while interesting , would not be cost efficient, energy efficient or reliable. The duty cycles and heat load requirements of the collection of functions are so far apart that a single system would be far more costly than separate systems. Refrigerators and clothes dryers are more cost effective as discreet systems. Combined DHW and space conditioning is common in Europe while in the US we have Daikin Altherma .

Answered by Jerry Liebler
Posted Jul 31, 2014 3:26 PM ET

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