As for the range hood I have not picked one yet, and it is not a big commercial stove

Well, no need to get one bigger than required. I have a Vent-A-Hood which removes 900 CFM where you would normally require the removal of 1200 CFM (haven't quite pinned down the ins and outs of that theory, yet), but it also has various speeds as I'm sure many do. My knowledge about the big hoods are that the fastest speeds are required to deal with a range fire, so you don't end up using full output much. I've used other big hoods that draw more than enough at the lowest rated speeds for smoky cooktop events.

i have done a significant amount of research and it appears that FBBP's post is right on the money.

Thanks for all the responses

jojo - Please come back later and let us know what you did and how it worked out.

FYI - One other thing I'm thinking about doing is have a direct vent with a motorized damper that will activate when the appliance turns on. In this case I'm thinking about putting the vent for make up air on the floor right under the dryer. Again the though is that even though the make up air will be unconditioned it will have a short path back out the house via the dryer exhaust vent when the dryer is in use. I still need to take a close look at balancing and integration with the rest of the house and my ERV. I'm looking at the whole house as a system and how everything will interact. Fortunately I've got several more years to work on the design. This forum has helped me considerably with all the experts providing advice!

Posted By MSG79 on 15 Mar 2013 02:28 PM
My understanding is that ERV/HRVs are no good for supplying make up air, because they always remove the same amount of air that they bring in, so you still end up needing make up air for that being exausted by a hood fan, dryer, or central vac. ...snip...

It is important to understand what an ERV or HRV consists of to understand how they perform.  Consider an HRV, since it is a little simpler.  It consists of two fans or blowers, one for intake air and one for exhaust air.  These are arranged such that they transfer heat across a cross-flow heat exchanger.  In the case of my Venmar AVS EKO 1.5 HRV, both fans move about 160 cfm (on high) at an external static pressure of 0.4 in. w.g.  So let's assume that with no other fans in the house running, they both flow 160 cfm against the static pressure of 0.4 in. w.g. due to pressure losses in the ducting.  Now when you turn on a kitchen fan and exhaust air, it unbalances the pressure differential between the house and the outside, and let us assume that the pressure for the intake fan is now zero (or less), but the static pressure for the exhaust fan is 1.0 in. w.g.  According to the spec sheet for my HRV, the flow for the intake fan is now 200 cfm (or greater), while the exhaust flow drops to 75 cfm, so the flows are no longer balanced, with a net inflow into the house of 125 cfm. 

So the flows for an ERV/HRV are only balanced if the user balances the flows at what we assume is no pressure difference between the interior and exterior air pressures.  Even for a perfectly balanced system, the flows become unbalanced as soon as a pressure differential is established across the envelope of the house.  The fans used in ERVs/HRVs are not magic -- they operate like any other fan with flow rate dependent on the pressure differential.  Thus, ERVs/HRVs will always tend to work toward balancing the pressure differential across the house envelope.  Depending on their size, and the magnitude of the pressure differential, they may or may not be very effective at offsetting the pressure differential, but they will always work in the direction of making the pressure correction.  Thus, they do tend to supply make up air for kitchen exhaust fans or dryers.

A dedicated make-up air line with damper might still be a good idea for a kitchen or dryer, but of course, that line offers no heat exchange before mixing with the interior air.

As already mentioned there is a huge difference in combustion air and make-up air.With sealed combustion appliances all air should be taken from the outside and then also vented to the outside for each appliance.By using this type of equipment eliminates the requirements for combustion air and also dilution air requirements from the mechanical room.Your home still requires mechanical ventilation to comply with ASHRAE 62.2 along with makeup air to offset any exhaust air being removed from the home.Serious health risk and potential fire risk exist if other gas burning appliances are allowed to burn within a negative pressurization zone, lack of combustion air,and a shortage of dilution air.Just opening a window even though it might cure the problems is not the answer.Carbon monoxide poisioning along with nitous oxides are serious problems within a tightly sealed structure.Design your home correctly and avoid the risk.Our homes should be the safest building that we vist.Protect yourself and your family.

Lee - Thanks for the insight. I will certainly give this some thought although it does differ slightly from what Paul Raymer, the author of [I] Residential Ventilation Handbook [/I] says. In chapter 8 he has a box to highlight a comment, which reads as follows: HRV/ERVs as primary ventilation systems temper their own air, but they should not be relied on to provide extra make-up air to the living space. They are designed as "balanced" systems, bringing in the same amount of air as they exhaust. They will not provide "extra" air for other appliances such as range hoods or fireplaces.

The book was written in 2010, so it is a bit dated. The reason I say what you and Paul say differs slightly is because he says HRVs should not be relied on and you say they tend to supply... . So, in the end I'm glad to know that an HRV can help to balance the pressure and even supply small amounts of make up air, but I don't think I'll rely on my HRV to supply all the needed makeup air for my house design.

acwizard - Your message is well taken and with the exception of my gas cook top I plan to use only sealed combustion appliances in my house. By the way, the author I mentioned above has been in the ventilation and consulting business for 30 years and is a full member of ASHRAE (a voting member of 62.2 SPPC) and the Home Ventilating Institute amoung other things.

They will not provide "extra" air for other appliances such as range hoods or fireplaces.

I have a Recoupaerator from UltimateAIr which has a pressure sensing module and is capable of balancing indoor/outdoor pressures through variable supply. However, as with all residential ventilators, we are talking about small amounts here. If you go over 200 cfm in a HRV/ERV, you are leaving residential and entering commercial territory and nearly every range hood, for example, will move that much or more. And, you don't want to get an HRV that is any bigger than you need or uses any more power than necessary as it runs quite a bit.