I was reading on another thread about ThermoDrain & PowerPipe to recover the heat from the water drains to pre-heat the incoming water into the water heater... I was wondering if there is a heat exchanger to recover the heat from bathroom fans and clothes dryer to also pre-heat the water heater, and maybe the air would also run through an ERV/HRV after?  Would lint from the dryer cause any issues with a heat exchanger?  There would also be a lot of moisture coming from the dryer and bath fans (moisture from shower). If this topic has been brought up before, please point me in the right direction.

Thanks,
Jere

There are tiny bathroom HRVs (ERVs not recommended, since you're trying to dump humidity, not preserve or balance it in bathroom ventilation.)

Dryers are particularly problematic from a condensation and lint/fire-hazard point of view. There are some cheap 4" diverter valves for redirecting dryer exhausts directly into the room, but that's a carbon-monoxide hazard for gas-fired dryers, and a humidity/mold hazard in general. It might be OK for electric dryers in very leaky houses or very dry climates, but room humidity would still have to be monitored, and a secondary lint trap (like a nylon stocking) on the output. In most places that's a code violation, but the products are still available over the internet.

The heat saved is quite modest- ~800kwh (~25therms)/year is typical for dryer use. Saving 1/4-1/2 half of that with a heat exchanger or diverter during the heating season is still not a big fraction for most families. In dry enough areas/homes that you could use a diverter you could save as-much or more by air-drying.

No air exchanger (I am aware of) recommends sending dryer or range hood exhaust through it (excessive temperature, moisture or grease).  Some brands recommend venting bath exhaust.  An HRV or ERV will lower winter humidity levels (when outside net humidity is lower than indoor net humidity). 

I have an EV200 (ERV) ventilating 2 bathrooms and the general kitchen area (not over range hood).  While the ERV recaptures a portion of the humidity to the exhaust air stream (in winter in WI) the net humidity of the house is lowered when the ERV is operating.

If the ERV was adding humidity to my house, I would not need a humidifier to maintain a base level of humidity in winter (WI).  (The humidifier was in the house when I moved in, the ERV was added later.)  I am recapturing @ half of my (total) exhaust moisture, instead of sending it all outside or down the drain with an HRV.  One bath shower may be temporarily exhausting 100% RH, but the other two vents are @ room humidity; in winter @35%, thus ave. exhaust humidity is 57%.  With indoor RH @ 50%, ave. exhaust would be 67% RH. 

My ERV as a central bath exhaust appliance accomplishes several things.  I have a whole house air exchanger and central exhaust in one unit.  The exhaust air now has 85% sensible energy recapture, which was all wasted previosly with exhaust only.  I now have "balancing air" for my bath exhaust.  I no longer have to listen to a noisy bath fan; a vent is ducted to the ERV.  My bathrooms and kitchen are ventilated better and are fresher than before. 

Always read and follow each manufacturer's directions and recommendations for their HRV or ERVs.  They are different. 

If your house is tight enough you shouldn't be needing to add winter humidity in WI (climate zone 6)- adjusting the ventilation rate should suffice. Often ventilation rates get set unnecessarily high just to avoid buildup of humidity, only to create winter dryness that would otherwise not happen.

Setting it up on dehumidistat control and allowing the indoor RH to rise to 30-35% is about right for health & comfort, and won't create undue hazard of condensation in the wall structures, assuming reasonable construction practices for vapor control are taken. See:

http://www.passivhaustagung.de/Passive_House_E/ventilation_and_humidity.htm

Humidifiers are notorious mold and bacteria growth & dispersion devices only to be used as a last resort. If you live in a tight house you're better off without 'em.

http://www.mayoclinic.com/health/humidifiers/HQ00076

Adding humidity to the house by venting the dryer exhaust inside of conditioned space is still a bad idea, even if you can remove the moisture with an ERV.

1) Ventilation rates are typically too low for optimum health.
2) Read it - they discuss 41% as good and 30% as too low
3) Tank type humidifiers can be a problem - some other types are fine.
4) No - good idea.

Could you tell me who makes the HRV for bathrooms? I can't imagine how this device could pay for itself....but curious

As everybody else commented, tying a dryer vent into HRV/ERV voids the warrenty and does not meet code in many states. I am not currently aware of any device that can recover heat from a dryer vent. Panasonic makes a room ERV called "whipser comfort spot ERV" that can be used for a bathroom. It is the only room/spot HRV/ERV that I am aware of. The other option is to tie into a whole home HRV which is another different ballgame. But I have another question on the same topic. Will an HRV balance the excess load of the dryer blowing air straight outdoors? I am working on a 900 SF home with a HERS rating of 17, and I am wondering what happens when the dryer causes the small, tight house to be under negative pressure. And, does anyone have opinions on the newer ventless electric dryers? Thanks! Jon

I know our HRV doesn't compensate for a dryer or kitchen exhaust mechanically in any way. But I can say a whole bunch more air comes in through it when the kitchen exhaust hood is running. I think it is the easiest way for the air to "leak" back in the house and I would rather have it come in that way than any other. I haven't tested it yet, but in thinking about it I wonder if the exhaust from the HRV slows down when the kitchen exhaust is on. It would only make sense that the HRV it would be working harder to push air out of the house and have a much easier time pulling outside air back in.

Panasonic

http://www.kitchensource.com/bathroom-fans/fv-04ve1.htm

very true.......... its best to know or control where the leakage occurs, most homes leak at the sill plate, if insecticides and herbicides are used around the perimeter of a home that whats getting sucked in to the living area

An electric condensing dryer makes sense to me. I'd like to see more discussion about them.

"I am wondering what happens when the dryer causes the small, tight house to be under negative pressure"-----, and would somehow either I would think that if your house is so tight that running a dryer would result in negative pressure, then perhaps you might suffer from lack of oxygen while sleeping? Just curious, because other vessels that tight include submarines, deep sea diving bells and space craft. Don't intend to sound like a douche, the statement just made me smile.

One question and a million different answers possible... many just because homes are not built the same all over the planet. Where I live... we build on basements.. where I build... mostly we do not spray insecticide... and I am real happy about that... though this last year... I took over a log home build that went up way too slow... and owners ended up needing to use some nasty chemical in some of the logs to kill off some built in infestations. I think I would rather kill with non insecticide somehow.... or borax or... CO...

Many sites say... a little negative pressure is OK.. I say.. who knows... I build on granite often... = radon...

One thing is for certain today but may not be soon... is we all die eventually... whether it is your house that takes you out... your crazy spouce, or forum poster.. or... Godzilla coming out of the screen of your new 3D TV!

What a fun forum... this is my fun post for the weekend... have a nice day people.

aj (who's dog in this show house... is a small time residential lakeside builder)

In My house the ERV is the weak link for infiltration.  When the range hood is on and the ERV is not on,  there is a signifigant flow of air  into the house through the ERV.  I think of it as my make up source of air when I am venting.  The dryer creates noticable flow through the ERV, but not as much as the range hood.  If the Range Hood is running, I can't light the woodstove unless I crack the door open.  It backdrafts like crazy and fills the room with smoke.
I need to add a make up air pasive vent to prevent this in the future.

Eric

Posted By Cgallaway on 19 Mar 2010 07:12 PM
"I am wondering what happens when the dryer causes the small, tight house to be under negative pressure"-----, and would somehow either I would think that if your house is so tight that running a dryer would result in negative pressure, then perhaps you might suffer from lack of oxygen while sleeping? Just curious, because other vessels that tight include submarines, deep sea diving bells and space craft. Don't intend to sound like a douche, the statement just made me smile.

Many houses are built tight enough these days that negative pressure from dryers can cause backdrafting of combustion equipment.  It doesn't take anywhere near submarine or spacecraft or diving bell tightness to be an issue. (If any of those leaked even 0.1% as much as a dryer's air flow it would be a disaster!)

It takes a LOT of oxygen to support a 10,000 watt burner (the size of a typical gas hot water heater), compared to what it takes to support a 150-180watt burner (a human at rest).  It would take a very small house indeed to "...suffer from lack of oxygen while sleeping"- something with a volume of a handful of coffins, maybe.  Even a heremetically sealed house would have several days worth of human respiration oxygen.

Increased CO2 concentraions over time would be a bigger (but still extremely small) threat to human physiology overnight, since CO2 regulates  respiration, and you'd begin to hyperventilate and end up suffering from too MUCH oxygen while sleeping.  In a very tight room that would be measurable in an 8 hour sleeping period, but in a whole house volume of air, not so much.

The bigger health threads from very tight houses have to do with accumulation of moisture- higher than human-healthy relative humidity (and mold conditions), trapping of unhealthy chemicals from cleaning fluids, combustion gas products, material-outgassing, radon, etc..  Ventilation rates don't usually have to be very high to handle the latter bits- water vapor is usually what calls for the larger ventilation rates to keep indoor air quality high in non-smoking households.

The ASHRAE recommendation for min ventilation rates in sleeping areas is 5 cubic feet per minute (which is at least 100x more than necessary to avoid oxygen deprivation issues).  A clothes dryer typically moves  on the order ~100cfm- enough ventilation to meet ASHRAE spec for 20 snoring people.