Does anyone know of any alternatives to venting the dryer to the outside? I would like to reclaim the warm (but problematic lint-filled, moist) air back into the home. Additionally, making another hole in the thermal envelope is not favorable. Suggestions?

Here is our low tech approach. Each fall, we disconnect the dryer vent from the window in the basement, insulate the window and place the dryer vent tube on the flow in the laundry room pointed at the floor drain. We then place a set of pantyhose around the vent tube, held in place with a very strong rubber band and replace pantyhose as necessary (maybe once a season).

We live in Denver, so the extra moisture is welcome in the house and haven't noticed any lint getting by the pantyhose. Definitely dumps a lot of heat into the basement laundry room.

There has been some concern that lint in the pipe might cause a fire hazard, but pipe seems to be pretty clear and functions as it does with the pipe vented to the outside. I'd make sure to replace the pantyhose as they clog up. We've done this for 5 to 10 years each cold season.

Denver Dave, please tell us you have an electric (not GAS!) dryer...

Yes I guess it is important NOT to be gas because of the fumes - we have an electric dryer.

Interesting. In addition to reclaiming the heat gain provided by a electric dryer, it might be even better to supply the dryer with outside air. I reckon a significant amount of inside warm indoor air gets pulled into a dryer and then exhausted outside. However, I am not aware of any dryers that have an intake option to supply outside air. I suppose no one worries about this heat loss given that dryers are only used a small amount of the time.

This has been discussed and one suggestion was a tube in tube heat exchanger for intake and exhaust. Be sure to account for clean-out and water drainage.

Would the tube in tube heat exchanger work for the exhaust pipe for the water heater and also the furnace. Quite a bit of heat is vented to the outside in winter, which is wasteful, but I also want as much heat vented to the outside in summer.

I tried cutting up a pop can and gripping the exhaust tube to perhaps radiate more heat - didn't work. Not sure if it isn't large enough or if I might be just insulating the pipe more.

found these:

Corrugated tube - might be feasible
http://www.hrs-heatexchangers.com/e...fault.aspx

Lots of tubes - don't see how this would work for exhaust.
http://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger

Posted By Myrtleboone on 09 Dec 2012 06:22 PM
Does anyone know of any alternatives to venting the dryer to the outside? I would like to reclaim the warm (but problematic lint-filled, moist) air back into the home. Additionally, making another hole in the thermal envelope is not favorable. Suggestions?

With enough digging you might find a source for an unvented condensing heat pump clothes dryer, which use about half the energy of a typical 'merican style dryer.  There have been versions available in Europe for more than a decade now, but are just now being pushed along by N-American energy policy makers.  The downside is longer drying times, but you don't have to poke a hole in your wall, and you can dispose of the condensate rather than over-humidifying the room air.

Electrolux is one of the bigger Euro-players that has market penetration in those types of appliances in the US, but SFAIK the do not (yet) sell condensing heat pump driers here. But you might want to ask a bit up the distribution food chain to see if/when they're coming.

Posted By Denver Dave on 10 Dec 2012 12:31 PM
Would the tube in tube heat exchanger work for the exhaust pipe for the water heater and also the furnace. Quite a bit of heat is vented to the outside in winter, which is wasteful, but I also want as much heat vented to the outside in summer.

I tried cutting up a pop can and gripping the exhaust tube to perhaps radiate more heat - didn't work. Not sure if it isn't large enough or if I might be just insulating the pipe more.

found these:

Corrugated tube - might be feasible
http://www.hrs-heatexchangers.com/e...fault.aspx

Lots of tubes - don't see how this would work for exhaust.
http://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger

I cannot speak for jonr, but some of the condensing natural-gas furnaces in this neighborhood use a single tube within a tube heat exchanger to preheat the fresh air within the exhaust gases. Imagine a single PVC exhaust pipe with a horizontal orientation. (Condensing furnaces have low exhaust temperature and high water content, so PVC is used for exhaust.) Now imagine that single exhaust pipe with a coaxial PVC pipe around it that is to carry fresh air to the furnace. Outside the house, the ends of the pipes should be different lengths so that you do not short circuit the the exhaust into the inlet. At the furnace end, you have to have a special Tee on the outer pipe to get the fresh air out of the pipe and into the furnace.

This approach may be out of favor now, as my furnace, which is newer than the ones that I have seen with this feature, does not have this type of heat exchanger on it.

Good ACEEE article. Note that it concludes:

The standard natural gas dryers demonstrate lower source energy consumption than any of the other technologies we tested.

And that the annual operating costs for typical usage varies from $100 to $40, depending on dryer type.

http://www.amazon.com/Miele-T8013C-Ventless-Electric-Condenser/dp/B000Y91DTY

I have a snap switch in the laundry closet operating a through-wall fan into the main bath in the winter, and through an ERV in the summer. Mieles are exceptionally well made, but it would have to last a looong time to recover the capital cost.

I am surprised that your RH hasn't increased in the laundry room let alone your entire house. I live in northern Maine on the Canada-US border so our humidity levels are very low in the winter months. I think the significant increase in humidity would wreak havoc on the mechanical heat recovery unit.

Posted By jonr on 10 Dec 2012 06:19 PM
Good ACEEE article. Note that it concludes:

The standard natural gas dryers demonstrate lower source energy consumption than any of the other technologies we tested.

And that the annual operating costs for typical usage varies from $100 to $40, depending on dryer type.

True, gas dryers are cheap and cheap to operate, but they don't address Myrtleboone's issue about eliminating holes in the high-R walls, whereas condensing heat pump dryers do.

Posted By Myrtleboone on 10 Dec 2012 10:01 PM
I am surprised that your RH hasn't increased in the laundry room let alone your entire house. I live in northern Maine on the Canada-US border so our humidity levels are very low in the winter months. I think the significant increase in humidity would wreak havoc on the mechanical heat recovery unit.

ERVs are designed specifically for managing high moisture loads. The only real issues with the high humidity & ERVs occur during icing conditions, but most HRV & ERV units sold in colder areas have automatic de-icing.

Running below 30% RH in winter is less comfortable and encourages transmission of airborne viruses amongst mammals. While it's not a good idea in stick-framed wood sheathed homes to humidify above 35% in winter, it doesn't take a super high ventilation rate in a super tight house to purge showering or internally vented dryer moisture peaks to keep it at 35% or lower. 

The bigger concern with venting a drier into the house is the suspended particulate air quality issue. (A nylon stocking lint-catcher is not exactly a HEPA filter.)

How about placing a HEPA filter at the exhaust rather than a nylon stocking?

Posted By Myrtleboone on 11 Dec 2012 10:07 PM
How about placing a HEPA filter at the exhaust rather than a nylon stocking?

Your drying efficiency would go to hell due to the higher impedance of the HEPA filter to air flow, increasing the amount of energy use.  Drying times have as much or more to do with the air volume movement as it does the heat added.  A nylon stocking is pretty low impedance (until it gets full of lint), but moving the 125-250cfm of a vented dryer through a HEPA filter would require a ridiculously large filter.


And you'd still be needing to move that moisture outdoors in a very tight house. While an ERV/HRV could keep up, it's still less than ideal to dump the moisture indoors.  Only fairly leaky houses or houses mechanically ventilated at a significant rate would actually NEED that moisture, even in the dead of winter.  A condensing heat pump based drier may in fact prove to be a better overall solution.  While the $1600 Miele may be a great unit, there are smaller versions out there in the sub-$700 range.   (I guess they're already here, if not heavily marketed yet!)

The installed cost of even bigger/better condensing dryers may be well under that of a standard vented gas dryer, since you don't have to run any gas plumbing.

My Miele condenser makes the bathroom toasty warm if you set the timer for an hour or two before you get up in the morning. But remember that it will produce heat of condensation in the summer, too, which would keep the airconditioner running longer. Dunno if it is a big deal. Humidity is a bigger issue in PA, but one hopes that the laundry process is roughly neutral when the water ends up in a tray.

OK, so maybe the benefit of dumping dryer air back into an air tight home is not worth the cost. If I traditionally vent the dryer to the outside, do you know of an insulating one-way system to prevent a majority of cold air to flow back into the dryer drum and surrounding area? I always have a draft creeping out from around and under our dryer. Thoughts?