Posted By nolanarcher on 24 May 2010 08:50 PM
I'm in the middle of renos for my house. We've installed a new HE wood stove, furnace, and hotwater tank already, and are about to add considerable air-tightness and insulation value to the walls, as well as replace all the windows/doors. Having read a lot on energy efficient housing, I wanted to get an HRV installed, because the ensuite bathroom doesn't even have a fan and the lower bathroom vents into the furnace room. With the old furnace gone, there is now a Bvent that could even be used to run the pipes for the HRV system, with convenient proximity to the stacking bathrooms and even the kitchen stove (it has a useless charcoal filter right now). I asked the furnace/hot water installer about it, and he said that's not how HRVs work. Afterwards I did more reading and thought he must have been wrong, so I called several HVAC companies until I found a couple who actually knew what HRVs were, and they came to have a look, and told me that you can't use HRVs in bathrooms or they will clog up with bacteria and excessive moisture and break down pronto. Then I did more reading, and it seems like other people are using HRVs in bathrooms all the time. What's the deal?

Some brands of air exchangers can be used for bath exhaust (always consult mfg. recommendations) . Some brands of ERVs can be used in the northern climates (and southern), while other brands suggest divergence of HRVs north and ERVs south.  (Again, follow each mfg. recommendations.)  
No exchangers I am aware of allow range hood exhaust, mostly due to grease, as well as high temperature air.  I have an exhaust vent in the kitchen (outside of a 45 degree angle from the top of the cooking surface, a universal guideline) going to my ERV (in WI, -11F design; unit made in WI) along with a vent in each of two bathrooms.  The fresh air is directed to my return plenum, while in my rental house, the fresh air is split to 4 different areas.  
No air exchanger provides make-up air for any open combustion appliance, (fireplace, water heater, wood stove, which require a dedicated combustion air source, as directed by their mfg.).  The ERV should be balanced.
There is no larger issue of biological growth in air exchanger ductwork versus bath exhaust fan ductwork, if both are installed properly.  There is biological growth potential with any air exchangers with drain pans, even without being connected to any bathrooms. 
My ERV has no drain, the ductwork is installed properly with no "catches"; no moisture accumulation, and no issues.  I do have "make-up" air for bath exhaust and general kitchen exhaust, with energy recovery.  I have a microwave/range hood combo for immediate cooking exhaust, and the ERV kitchen vent removes the cooking odors and added moisture overnight. 
The variables are the amount of run time, and amount of air exhausting from each location.  Minimum code (which is always minimum) in WI is 50cfm intermittent or 20cfm continuous per bathroom.  Also, code is to provide "balancing air" calculated of 40% of the total of bath fans and range hood cfm. 
With exhaust only fans, an industry guideline is 1cfm/square foot or 8 air changes (evacuations) per hour.   
As houses have reduced infiltration (built tighter), air has to come in from somewhere.  Otherwise we are building vacuum pump houses and air will come back in through the biggest holes; water heater, fireplace, dryer vent, etc. 
Reduce exhaust only fans/vents, utilize closed combustion appliances, apply make-up air as needed. 

Posted By Ventolator on 01 Jul 2010 05:56 PM

Some brands of air exchangers can be used for bath exhaust (always consult mfg. recommendations) . Some brands of ERVs can be used in the northern climates (and southern), while other brands suggest divergence of HRVs north and ERVs south.  (Again, follow each mfg. recommendations.)  
No exchangers I am aware of allow range hood exhaust, mostly due to grease, as well as high temperature air.  I have an exhaust vent in the kitchen (outside of a 45 degree angle from the top of the cooking surface, a universal guideline) going to my ERV (in WI, -11F design; unit made in WI) along with a vent in each of two bathrooms.  The fresh air is directed to my return plenum, while in my rental house, the fresh air is split to 4 different areas.  
No air exchanger provides make-up air for any open combustion appliance, (fireplace, water heater, wood stove, which require a dedicated combustion air source, as directed by their mfg.).  The ERV should be balanced.
There is no larger issue of biological growth in air exchanger ductwork versus bath exhaust fan ductwork, if both are installed properly.  There is biological growth potential with any air exchangers with drain pans, even without being connected to any bathrooms. 
My ERV has no drain, the ductwork is installed properly with no "catches"; no moisture accumulation, and no issues.  I do have "make-up" air for bath exhaust and general kitchen exhaust, with energy recovery.  I have a microwave/range hood combo for immediate cooking exhaust, and the ERV kitchen vent removes the cooking odors and added moisture overnight. 
The variables are the amount of run time, and amount of air exhausting from each location.  Minimum code (which is always minimum) in WI is 50cfm intermittent or 20cfm continuous per bathroom.  Also, code is to provide "balancing air" calculated of 40% of the total of bath fans and range hood cfm. 
With exhaust only fans, an industry guideline is 1cfm/square foot or 8 air changes (evacuations) per hour.   
As houses have reduced infiltration (built tighter), air has to come in from somewhere.  Otherwise we are building vacuum pump houses and air will come back in through the biggest holes; water heater, fireplace, dryer vent, etc. 
Reduce exhaust only fans/vents, utilize closed combustion appliances, apply make-up air as needed.