pfennig:
We are finishing the design of our new house which will be very tight (though not SIP construction). Here in Minnesota, an energy recovery ventilation system is mandatory according to code. Our architect has specified that no bathroom exhaust fans or stove hood be used. The ERV blower can be timer-switched into high mode from a switch in the bathroom or kitchen. There are disadvantages to this (potential grease build-up in the ERV exhaust lines from the kitchen) but it maintains the ventilation and pressure integrity of the house. We never fry on the stove anyway, and don't plan to start in the new kitchen.

Installing a 300-900 CFM exhaust hood over the stove would depressurize the house. Most ERV units couldn't fully adjust to the exhaust fan's outflow. Unless you open a window, you'd create a pretty strong backdraft down your chimney if you have one.

Aren't bathroom fans and stove hood(36" or more) required under your code?? It is here at least.

No vent in bath or kitchen? I'm amazed that that's allowed in any US jurisdiction.

I'm using radiant floor, no AC [not needed at this elevation], but because the house is tight I'm using a heat recovery vent. It draws air from all the baths on demand [each has a push button timer] as well as a couple central locations on a constant basis.

I think indoor air quality plays a massive role in quality of life, and one that people often overlook-- bad air leaves you stuffed up, tired and irritable; yet we often assume we're just having an off day, or picked up a virus, etc.-- cause and effect often go un-discovered.

EWw with only 300-900 CFMS on your hood I would get used to the idea of smelling burnt popcorn or overcooked bacon for days in your home...

We have an envelope seal on our large home and added the Fresh air system into the HVAC system so that whenever the air/heat kicks on, so does fresh air. We still have exhaust fans in the bathrooms... I have a 1200 roof mounted hood fan for the range. I did not want to have "worry" about fresh air intake so we added to system. It was about 4000.00 and had its own air vents in addition to existing heat/ac vents.

We are in Minnesota and have bath and kitchen vents. We have an ICF house and geothermal heating and cooling. We have an air exchanger that is running 100% in the winter. We just backed it off to 90% a few weeks ago. Our HVAC guy says to turn it off in the spring when we start having our windows opened more often.

Right after we installed our carpet, I was getting sick. Bad headaches, nausea, just general malaise. I thought it was the carpet. We weren't living here yet, but I was in the house nearly all day, sometimes 12 hours a day. Come to find out, our HVAC guy was checking the air exchanger and he hadn't closed it well enough. It wasn't working at all. We had our doors and windows closed, as it was the dead of winter. Once we got it going again, I was fine.

It's good that everyone is agreeing that an air exchanger is necessary even though it is often overlooked. An energy-recovering one is even better (not sure if they even make any other kind).

duluthjeff's system sounds very strange to me (and several other posters as well apparently). I wouldn't think using the air exchanger exhaust for the kitchen vent _or_ the bathroom vent would be acceptable. The CFM would probably be too low for 'proper' kitchen usage, the run from kitchen to air exchange unit could easily be too long or sloped the wrong way, fire risk would be greatly increased, condensation risk would be greatly increased, system life could easily be compromised (I _do_ like to fry and blacken things on the stove) and it would be very easy to 'accidentally' pipe burnt roast smells into the master bathroom or something. It just doesn't seem to be a reasonable solution.

teddas, you said:

I have a 1200 roof mounted hood fan for the range. I did not want to have "worry" about fresh air intake so we added to system. It was about 4000.00 and had its own air vents in addition to existing heat/ac vents.

Are you saying you added a separate system to allow fresh air intake to allow your powerful kitchen vent? This is the first I've heard of a system with its own vents separate from the normal hvac ducts/vents. This is a separate air intake system to allow the kitchen exhaust vent to draw correctly by bringing in exterior air, similar to what I proposed in my original post, "some kind of external air intake for internal bathrooms, that can be "opened" when running a vent"? Or am I misinterpreting you?

minnt, your situation sounds exactly what I was concerned about: tight envelope, air exchanger, supplemental vents for baths and the kitchen. What steps or design decisions do you use to make sure that everything works even when you have the house tightened up for winter? How do you prevent the kitchen vent or bathroom vent from depressurizing the house and backdrafting your chimney (assuming you have one)?

Given that things like kitchen and bath (and clothes dryer) exhausts must be short runs for fire and condensation reasons, I can't see how one could incorporate all of them into a energy recovery ventilation system unless you somehow had a separate energy recovering air exchanger for each vent - this does not seem reasonable financially, and I have not seen or heard of this being done, but I suppose it is possible. So for my particular house plan (3 bed, 2.5 baths, The only alternative I can think of is to simply ditch the idea of energy recovery and have a direct vent from the exterior come into the house somewhere (into the normal AC for dehumidification purposes hopefully). When you switch on a bathroom vent or the kitchen vent, this intake opens and the HVAC system kicks in to suck the appropriate amount of exterior air into the house to avoid depressurization and backdrafting. That exterior air will be as hot, cold, humid, or smelly as the exterior is, no way to recover the energy being vented from the kitchen/bath.

It's essentially a special window with a fan that can be automatically opened by the HVAC system when necessary. But does such a thing exist, integrated into the controls of modern HVAC systems? The bathroom and kitchen exhaust controls would have to be integrated into the system for proper operation, and I haven't seen any systems like this yet.

Am I the first to propose such a system? Should I patent this idea? :-)

Just want to comment that a 1200cfm range hood for the kitchen is on the high end for ventilation. In fact the most powerful system ventahood offers is 1200cfm. 600-900cfm is perfectly adequate depending on the size of the range and intended usage, and in no way merits an "ewww", IMHO.

Becuase my house is so tight, We have a seperate fresh air system that sucks from the roof and has its own seperate vents put in many rooms througout the house. it is connected to the HVAC system so it runs whenever the system turns on. We do not want to have to manually turn on anything or open windows.
We just included a higher CFM range hood to ensure adequate ventilation hence no burnt popcorn lingerings. In a closed house you WILL have a EWWW smell with burnt foods. We also did this as we had to make one of the fireplaces ventless. We did the 4.5 inch open cell foam thoughoutand even thicker 6-8 in roof.

Get the load calculations done by someone that knows what they are doing. All the ICF homes I have done come in somewhere about half of what the contractors are trying to guess at it. It all depends on the windows and exposure.

Most end up with two stage equipment and zoning systems because of building volume and low air flow requirements.

I'm not sure I'm following this, but I don't think bath vent runs to be short. They can be integrated into a single HRV system.

Th kitchen vent is different, of course. I'm actually considering using a very small vent for makeup air beneath the range. Seems to me that this would be the ideal spot for the fresh air to create a current of air that would trap smoke and odors effectivly. The idea of opening a window in the area for makeup air seems inefficient on many levels.

I don't think a mechanical device to give the HVAC control the ability to open a window makes much sense-- Just not cost effective compared to a small, simple vent. Some remotes for window shades cost hundreds, and for whole window you'd need a much more mechanically robust system.

We also have an HRV that works for the whole house. Bathroom ad kitchen vents were not required or recommended with the design. We haven't noticed a lasting smell from any food we cook but we don't do a lot of burning either ;)

Actually we have a wood stove and it backed up smoke into the house one day when there was foggy weather outside and the HRV system cleared it out quickly. We opened a window to see if that would help and it slowed the flow of smoke down a lot. Maybe b/c it was competing with the system? Anyway, we're pretty happy with the results.

We have a geothermal system in an ICF (to the top of the 1st floor) house with an HRV. We have separate venting for the kitchen cooktop, a direct vent gas fireplace, and makeup air for the woodstove. All bathrooms are on the HRV system. I'm a little fuzzy on the insulation, since DH kept changing his mind. In the dormers and gables of the 2nd floor, we have baffles with I think a combination of 1" of whatever that expensive polywhatever is in the attic, along with blown-in cellulose, and 1" of XPS on the outside. Everything was built and inspected according to our state's code which incorporates the IRC 2003 code, which has since been updated.

DH researched this a LOT, and asked lots of questions of HVAC installers, suppliers, and manufacturers. There were times when he had to explain some of it to the inspector. He thinks he got it all right, although I remember him getting conflicting views on whether we should use an HRV or ERV, since apparently we're sort of on the border climate-wise as to which one is most suitable.

Anne

Hi all, very interesting reading. My architect assures me that the ERV system properly sized will easily handle the requirements for bathroom venting. Each bathroom would have a "high vent" timer switch that kicks the ERV into a higher CFM state.

I also have some qualms about using only the ERV system to vent the kitchen, your comments are cautionary.

Those of you with tightly sealed houses, why does turning on an exhaust fan or hood not cause significant depressurization problems for you? The ERV system is balanced in terms of air in vs air out. Adding 300-1000 CFM out would either make your chimney (if you have one) pull in the equivalent amount of air, or your house would reach a lower than atmospheric pressure which would (in a perfectly sealed system which I realize is not achieved in practice) eventually cause the exhaust flow to stop.

Just some musings on the physics.

If you've ever seen the grease build-up in a kitchen vent filter, I think you'd think twice about using your regular house ERV in place of the kitchen vent.

I know that I personally would never buy a house without active kitchen and bathroom ventilation. But then I'm an active cook. Maybe it's not a big deal for folks who don't cook much.

I didn't read all the posts, but below you will find a FAQ from the Appliance Forum that talks about vent hoods and make up air.

Here is a link that might be useful: Vent Hoods and Make Up Air