recapturing dryer heat?

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Has anyone tried to use a heat exchanger of any kind on their dryer vent, or better yet, is there any commercially available product to do this? I have a gas dryer so simply venting indoors likely isn't a good option, as welcome as the extra humidity may be the few months out of the year that I'd actually want to do this.
I realize that it's probably inconsequential in the grand scheme of things, but it does seem wasteful to heat all that air and then just blow it outdoors when it's 20 degrees out.
I tried to do a quick online search, but all I saw was a little discussion and not much in the way of actual plans, products, or results.
nate
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my dryer had some rotten cardboard lining the inside of the door that served to insulate, i ripped that off, now the front door gets nice and hot so some heat is recovered there..
also use an extra long METAL vent hose and a lot of the heat will be recovered that way too....
if you put any significant money into this, it is unlikely that you will get a return on the investment..
Mark
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wrote:

You don't want to recover TOO much of the heat unless you use a "condensing" heat exchanger, otherwize the moisture you took out of the clothes is going to run back into the dryer or make a big icycle at the vent.
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wrote:

Could make a J tube of sorts, to catch any condensate.
I think the suggestion about using more ducting was good. It's perty cheap, and you can just run it around all the floor or ceiling corners, or some kind of serpentine config.
Unless you can control the humidity, that warm air is just too damp to vent inside.. They make indoor lint traps (water baths), and even with those, we eventually just vented it right outside.
Ditto "ventless" gas heaters -- they'll soak a wall.
Proly the best thing for saving money on a dryer: A front loader with a high-rpm spin cycle. You can almost hang the clothes right out of the washer. Rarely do you find a win-win-win-win-win-win situation as with front loaders.
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wrote:

It takes very little additional ducting to destroy a dryers performance. Add 10' and perhaps a bend or two and you'll be looking at two hour dry times.
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wrote:

Duct booster? Heh, starting to get complicated already....
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On Fri, 15 Jan 2010 00:12:25 -0600, AZ Nomad wrote:

I'm running about 8' and a couple of 90-degree elbows and it's not bad - about an hour for a full load (electric dryer). No condensate issues, either (I sited it in the basement right next to where the sump pump will be going, just in case).
One thing that is worth doing is dismantling the dryer every couple of years; they really plug up after a while, even if the airflow coming out still seems good. Sometime I'll get a wild hair and make a proper access panel for the back of ours (the whole back has to be removed right now, plus it extends underneath the machine so the whole lot has to be turned over to get inside)
I've thought about recovering heat from ours in the past, too (as recently as a week ago, actually) - but I'm just not sure that it's worth it, at least not for anything that uses power to do the recovery. We run the dryer for around an hour a day, and given the 23 hours it's not running, I'm probably better off insulating the heck out of the pipe to reduce heat loss from the house, and save more money that way.
cheers
Jules
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On Fri, 15 Jan 2010 10:36:01 -0600, Jules

The previous poster was suggesting more than 8' and a couple of 90 degree turns. He'd be lucky if he managed to dry a load of clothing in under 5 hours and if the dryer didn't shut down due to overheating.
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Jules wrote:

I have "restored" a couple of "non-working" dryers by taking outside, and blasting out all the air passages with a large blaster nozzle on my air compressor hose. You'll be amazed at the crud that comes out. After that, they worked fine.
O.P. If you add duct to extract more heat, use a larger size duct so you don't restrict the dryers air flow.. This will also give it more heat exchange area. Just make sure you clean out the inside regularly, or it will become insulated with lint, and become a fire hazard.
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Bob F wrote: ...

Somebody else mentioned a fan to move air over the existing duct -- I' think a combination of a larger piece of duct around the existing w/ an airflow down the resulting annulus would create a counterflow exchanger w/o having to worry about filtering lint nor the possibly excessive humidity.
$0.01, etc., etc., etc., ...
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I love it when everybody has such a fountain of advice that they've never actually tried. The anal vapor is overpowering.
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On Fri, 15 Jan 2010 17:34:52 -0600, AZ Nomad

Well, this last suggestion is actually something that IS used, very often, in another application. It is used on almost all certified light aircraft and many experimental aircraft to extract heat from the exhaust to warm the cabin and also provide carburetor heat.
Wrap a couple coil springs (like screen door springs) around the vent pipe, then wrap a sheet of aluminum around that to make a larger duct over top of the spring. Cut a hole in the middle of the outer skin and force air in or draw air out and the air will be heated by transfer from the inner "skin" to the spring and the outer "skin", and from all 3 to the air passing over.
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wrote:

sure. name one instalation.
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a> wrote:

He just did!
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wrote:

He just did! ================================== AZ Nomad belongs with the other dick-wavers over on alt.hvac.
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wrote:

No he didn't. He pulled out of his ass a bunch of bullshit.
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On Sat, 16 Jan 2010 12:35:26 -0600, AZ Nomad

Go back to the desert you old Arizona Hippy.
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AZ Nomad wrote: ...

Never heard of reheat cycle I take it???? :(
Just postulated a very simple implementation of concept.
"The Brayton Cycle with Regeneration, Intercooling, & Reheating Section 8.9-10 By: Denise Lane ME 372 Thermodynamics ... The Brayton Cycle with Regeneration
In gas-turbine engines, the temperature of the exhaust gas leaving the turbine is often considerably higher than the temperature of the air leaving the compressor. Therefore, the high-pressure air leaving the compressor can be heated by transferring heat to it from the hot exhaust gases in a counter-flow heat exchanger, which is also known as a regenerator or recuperator."
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On Fri, 15 Jan 2010 20:40:34 -0600, AZ Nomad

I gave you TWO very common uses of the "technology"
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Nate Nagel wrote:

It's one of those things that has been contemplated for eons. The reason that there is not a product for the purpose is that there are too many issues to overcome, like humidity, condensate, corrosion, back pressure, lint buildup, etc. and too little to gain, something like 15,000 BTU for 30 min.
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