We're in the process of installing a geothermal system for new residential construction and ran across a question regarding bath area ventilation. The question is not specific to geothermal, but I couldn't find a better place to post it.

Has anyone that's installed an HVAC system in a very tight house, and installed an ERV in conjunction with that system, gone on to use the ERV to ventilate the bathrooms in lieu of individual bathroom fans?

I've run across this concept before and spent a little bit of time trying to find links to post here that discuss this, but have been unable to so far. The Home Ventilating Institute (hvi.com) has some info on it, but nothing I've been able to point to for purposes of this post.

Thnx in advance.

We tend to connect our HRV's to HVAC duct system. That allows you to multi task something you are already paying for.
Connecting to bath fans or clothes dryers in our climate can bring on a few condensation concerns and actually require more ductage than conventional exhaust set ups.
J

Look at the Honeywell ER200 instructions on their website. It can be configured to exhaust the bathrooms. You may need more cfm though depending on bathroom size and qty. Maybe the central ERV plus an additional small exhaust fan in each bath may work in that case. I think you need dedicated, smooth, self draining returns from the baths to the ERV, so location of the erv may not work for your app. Buidlup of condensate is a concern. I looked into this a while back, but never proceded on it.

Thnx for the input.

Still struggling with this decision. Have run across at least one model that describes how to accomplish exactly what I'm referring to, but they don't address the condensation buildup issue. They indicate the following in their installation manual:

"Can an ERV be used to ventilate bathrooms?

A xxx ERV can be used as a central exhaust system in place of bathroom exhaust fans. Tie a grill in each bathroom directly back to the ERV – see Schematic (A). A successful installation should provide at least 50 CFM of exhaust per moisture producing bathroom. When used for bathroom exhaust, the xxx should be used for only one bathroom, the xxx should be used for no more than two bathrooms, the xxx for up to four bathrooms and the xxx for up to six bathrooms. Install a control in each bathroom ventilated by the ERV (see Secondary Operating Controls, below)."

You don't say where you are building, which is important: http://www.achrnews.com/Articles/Feature_Article/cf9b3788e7f4b010VgnVCM100000f932a8c0____
If your climate is warm enough, you shouldn't have an condensation issue with ERVs, which move moisture from the more humid air stream to the less humid one and thus don't need condensate drains or defrost cycles as HRVs do.
Look at power dampers and on-demand timers for control. (i.e. You punch a button; the damper powers open and the ventilator runs for a specified time period.) Here is a package approach using a whole house ventilator: http://www.iaqsource.com/article.php/bath-ventilation-with-hrv--smart-move/?id=88
Or install a small stand alone ERV to ventilate baths and kitchen using on-demand switches and power dampers. http://www.iaqsource.com/category.php/aprilaire/?category=789
A caveat: ERVs need balanced air flow to work properly. If you have a wide disparity in exhaust runs, you'd want to hire an installer who understands the math.

Posted By toddm on 11 Dec 2010 11:44 AM
You don't say where you are building, which is important: http://www.achrnews.com/Articles/Feature_Article/cf9b3788e7f4b010VgnVCM100000f932a8c0____
If your climate is warm enough, you shouldn't have an condensation issue with ERVs, which move moisture from the more humid air stream to the less humid one and thus don't need condensate drains or defrost cycles as HRVs do.
Look at power dampers and on-demand timers for control. (i.e. You punch a button; the damper powers open and the ventilator runs for a specified time period.) Here is a package approach using a whole house ventilator: http://www.iaqsource.com/article.php/bath-ventilation-with-hrv--smart-move/?id=88
Or install a small stand alone ERV to ventilate baths and kitchen using on-demand switches and power dampers. http://www.iaqsource.com/category.php/aprilaire/?category=789
A caveat: ERVs need balanced air flow to work properly. If you have a wide disparity in exhaust runs, you'd want to hire an installer who understands the math.

Thnx for the response. 

The location is about 45 miles southwest of Knoxville, TN.

I haven't seen anything yet on power dampers which may work for this application. The website you reference (http://www.iaqsource.com/article.ph...ove/?id=88) has some great info on this concept.

I may have a wide disparity in exhaust runs so I'll have to disuss this with the installer when I see him next. My thought is to use this concept (if it works) for the bathroom areas. The kitchen exhaust fan over the range top will be moving more air and is ducted right out the exterior wall it's installed on. The only question there is the make-up air it'll require.

Thnx again for the comments.

Posted By Scewter on 07 Dec 2010 10:10 PM
We're in the process of installing a geothermal system for new residential construction and ran across a question regarding bath area ventilation. The question is not specific to geothermal, but I couldn't find a better place to post it.

Has anyone that's installed an HVAC system in a very tight house, and installed an ERV in conjunction with that system, gone on to use the ERV to ventilate the bathrooms in lieu of individual bathroom fans?

I've run across this concept before and spent a little bit of time trying to find links to post here that discuss this, but have been unable to so far. The Home Ventilating Institute (hvi.com) has some info on it, but nothing I've been able to point to for purposes of this post.

Thnx in advance.

Yes we do many of these type of ventilation systems.
We only use the ERV's because they can be ran throughout the year and they don't have a condensate drain to worry about.
But, according to our city code; this unit can be used for fresh air, bathroom exhaust, a kitchen intake in the kitchen but not necessarily connected to a range hood and it also cannot vent a dryer.
Ducting: you size it accordingly to the CFM you are trying to move, just like a heating/cooling duct system!! Fairly simplistic if you are familiar with duct systems.

We came across a system with a wood fireplace installed which we overlooked at. When the unit was not operating, strong winds would creep in the house and go out the chimney causing a draft. We had to install a backdraft and a zone damper to seal up the unit in the off mode, works good now.

The important part is getting the right size unit (CFM/static pressure).

Posted By arc8 on 16 Dec 2010 11:42 AM

Posted By Scewter on 07 Dec 2010 10:10 PM
We're in the process of installing a geothermal system for new residential construction and ran across a question regarding bath area ventilation. The question is not specific to geothermal, but I couldn't find a better place to post it.

Has anyone that's installed an HVAC system in a very tight house, and installed an ERV in conjunction with that system, gone on to use the ERV to ventilate the bathrooms in lieu of individual bathroom fans?

I've run across this concept before and spent a little bit of time trying to find links to post here that discuss this, but have been unable to so far. The Home Ventilating Institute (hvi.com) has some info on it, but nothing I've been able to point to for purposes of this post.

Thnx in advance.

Yes we do many of these type of ventilation systems.
We only use the ERV's because they can be ran throughout the year and they don't have a condensate drain to worry about.
But, according to our city code; this unit can be used for fresh air, bathroom exhaust, a kitchen intake in the kitchen but not necessarily connected to a range hood and it also cannot vent a dryer.
Ducting: you size it accordingly to the CFM you are trying to move, just like a heating/cooling duct system!! Fairly simplistic if you are familiar with duct systems.

We came across a system with a wood fireplace installed which we overlooked at. When the unit was not operating, strong winds would creep in the house and go out the chimney causing a draft. We had to install a backdraft and a zone damper to seal up the unit in the off mode, works good now.

The important part is getting the right size unit (CFM/static pressure).

What part of the country do you install these?

Also, I'm interested in using a zone damper as you mentioned - any reccomendations?

Thnx for the response.

North Dakota/Minnesota area.

If the house is sealed tight; the ERV is self balancing, you should not have to install any dampers! On the other hand, if you have appliances (IE as a wood open Fireplace), then you would need a setup like I've mentioned. All other exhaust appliances should have their own backdraft dampers!

 

I too was planning a ERV for my retrofit but decided to hold off until we see how the rest of the retrofitting worked out. I too have a stove fan that I will need to address as I tighten up the house.
For a new house, I think as long as you ran the control wires as well as power during rough in, you could get a feel for how much you'll be using as you live in it. Since 2 of my 3 bathrooms have windows, the fan doesn't get used much in the existing units. I also found out that the 1st floor 1/2 bath that had an exhaust fan in it since new never had any ductwork. Just the joist space above it.
Anyways, exhausting all the air from the bathrooms to make a ERV work would make the house too dry IMO. Just the switch from electric baseboard to forced air GEO has dried things out. The cat water tray needs over twice what it has before. And my humidity indicators are lower too.

How has heating air using hot refrigerant gas flowing through a sealed coil dried the house any more than heating air via electric baseboards?
Neither source of heat affects absolute humidity in the least bit.

Sources of heat which affect indoor humidity are: 1) Unvented gas appliances - before they kill you, they moisten the air. 2) Vented combustion appliances using house air for combustion - cold dry make-up air infiltrates from outdoors, lowering humidity.

If with baseboards you were shivering at 60*F dreading the power bill, but with geo you are living large at 68-70, then absolute humidity is unaffected but relative humidity drops with the increasing temperatures, but baseboards operated at the same setpoints would have the same effect.

Don't blame geo for being dry.