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During winter we run a gas-powered heater and evaporative humidifier to maintain indoor air quality.

Meanwhile, every day (big family!) we run a gas-powered clothes dryer which dumps hot, humid air outside.

Are there any gas-powered dryers that are so efficient that they can be vented indoors (like vent-free fireplaces)? Or is there a way to split the combustion vent from the dryer vent stream so the former goes outdoors and the latter can be redirected into the central air handler?

Or is the amount of energy spent on the dryer inconsequential compared to what a 98% AFUE central gas heater wastes?

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    Probably a bad idea. The amount of moisture dispelled by the dryer, is likely too much to put back into your home. Extracting the heat from the exhaust can be a dangerous game, and may have a higher cost than it's worth. – Tester101 Nov 20 '14 at 15:51
  • The one thing I have no doubt about is that the humidity is worth saving. Our central humidifiers struggle running non-stop during heat cycles to keep indoor RH above 30% when the outdoor temperature is below freezing. – feetwet Nov 20 '14 at 16:14
  • There are electric ventless driers homedepot.com/p/… – s0rce Nov 20 '14 at 17:50
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    A very simple solution may be to just set up a drying rack indoors. In a heated house with dry winter air, your clothes will probably dry rather quickly, adding their moisture to your indoor atmosphere. And then you don't use the energy to run the dryer in the first place, but leave the heating to be done by your (hopefully more efficient) furnace. If you find the clothes too stiff at the end, you can run them through a quick no-heat fluff cycle on the dryer. – Nate Eldredge Nov 21 '14 at 1:44
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The dryer vent and the combustion vent are one and the same. If you try to use the dryer vent for heating you will have two issues, first excess moisture and second carbon monoxide. Gas dryers get their efficiency by directly venting the combustion into the damp clothes which then by the way of evaporation drastically reduces the temp of the heat. It would be near impossible to modify a dryer to separate the combustion from drying.

Then there is the idea of using a heat exchanger to extract the excess heat. But I don't recommend it since there really isn't enough excess heat in the line to keep the temp above 100C/212F at the vent exit (below this you risk condensation). If you get condensation on a cold day, you then risk ice, which then risks blocking the vent, which then risks carbon monoxide poisoning.

Also take a look at the fact there isn't any commercial products to do this. This speaks to how unfeasible it is to use this waste heat.

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    Plus any heat exchanger will clog up with lint over time, creating a fire and backdraft hazard. – Fiasco Labs Nov 21 '14 at 2:42
  • There are plenty of commercial products that do this -- they have flap on a pivot that can direct the stream of hot, humid air back into the dwelling (in winter) or outside in summer. – gbronner Nov 24 '14 at 13:16
  • @gbronner - he was talking about heat exchangers not being available, not vent re-directors. – AJ Henderson Dec 1 '14 at 20:25
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Yes, my parents have had one of these gadgets since the 1980s:

http://www.acehardware.com/product/index.jsp?productId=1273159 http://www.amazon.com/Dryer-Heat-energy-Saver-aceex12/dp/B000H5PTI6

At the time, I seem to recall that running the dryer was something like 10k BTUs, which was significant.

However: new washing machines spin much faster, and extract much more water, meaning that you should wind up using your dryer much less than before, making this less worthwhile.

Also, we use this to vent into a relatively large basement, so we don't have to worry about condensation.

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    Yes, I used one of those when I had an electric dryer. I don't believe it's safe to use with a standard gas dryer, although that is part of the original question. – feetwet Nov 24 '14 at 13:26
  • I've never seen any warnings about this, and they were retailed through catalogs for decades. The ACE hardware website doesn't have any such warnings either. – gbronner Nov 24 '14 at 13:35
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    I just checked the installation instructions on my gas dryer and they say it "MUST BE EXHAUSTED OUTDOORS." – feetwet Nov 25 '14 at 14:20
  • Their lawyers talking... You could leave a carbon monoxide alarm near the diverter box. We've been doing this for 30 years with no ill effects. – gbronner Nov 25 '14 at 14:40

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