Can an HRV replace the air exhausted by a range hood?

Question

I'm in the process of buying a 1950s ranch house. It doesn't have the greatest insulation, so I'm planning to do some improvements over the first few years to tighten things up. I'll certainly do the basics (expanding foam in window openings, gaskets behind outlet/switch covers, rigid foam sealed with expanding foam along the rim joists in the basement, an extra foot or more of insulation in the attic, rigid foam on the basement walls, new weatherstripping where needed). I live in Michigan, so we do have a real winter with snow, and a few days in the summer where it will get hot enough to turn on the AC, so anything to save money on energy bills is great.

I've been reading about the issues you can run into when you seal up a home TOO tight, such that you don't have enough fresh air in the house. I'm not sure I'm going to run into these, but then I'm not sure how good a job I'll be able to do with the above-mentioned improvements. If it comes to it, installing an Energy Recovery Ventilator or Heat Recovery Ventilator (ERV or HRV) is something that I would consider in the future.

All of this leads me to my main question: I like to cook. I would like to put in a fairly powerful range (nothing huge, though; I don't need six burners and a griddle), and will need a hood that can carry smoke, heat, steam, grease, etc. from cooking out of the house. I don't want absurd overkill, but I don't want my smoke detectors going off when I roast a chicken. It looks like I will be looking at hoods around 650-800 CFM (see my other question).

The air that goes out the hood has to come from somewhere. Will an HRV flow extra intake air if there is a pressure imbalance caused by extra air being exhausted elsewhere in the house? Will it flow enough extra intake air to supply the hood I'll need for the above? Chances are, I'm not going to have the hood on high unless I'm cooking something that produces a lot of heat/smoke, or cooking for lots of people (things I do regularly, but not every day). Would it OK to run the fan on low/medium most of the time, and open a window when I need to turn it up? Or do I need to look into providing dedicated make-up air?

Am I just over-thinking all of this and I'll be fine because there's no way I'll ever be able to seal an existing house up enough that this is a concern?

Answer 1

Are you going to run your kitchen hood exhaust through your HRV? I don't think that is an approved configuration because of the grease in the exhaust. Let's assume you don't for the 2nd part of this answer.

An HRV tries to recover heat from air exhausted through the HRV and use it to warm incoming air. When running your kitchen hood, no air will be exhausted through the HRV so the HRV will be acting like an open window: fresh air will come in through it but it will not be warmed.

During a cold winter, I assume you would find this situation (cold outside air distributed through your house) to be uncomfortable and undesirable.

All the literature I have seen assumes you want to take the cold outside air, hundreds of CFM, and heat it up to 70F so that you can turn around and blow it outside. Equipment capable of doing this is expensive and it seems wasteful of energy.

In my house, I have two windows right next to the hood and I just open the windows when I use the hood. Outside air comes in, mixes with the cooking fumes and goes right out. Standing in front of the range is a little colder than the rest of the house but at the same time, you have the heat from the range so it's not a big deal in my experience.

The bottom line is to consider if you want to heat your makeup air and if not, bring it in as close to the hood as possible, but in a way that helps capture the cooking fumes and doesn't just bypass the range.

Answer 2

Lack of adequate incoming air is a definite concern with any high-powered range hood or another ventilation appliance that exhausts house air to the outside. So, you're not "overthinking" it, it can be a problem.

What will happen in a situation with a high-power (700+ CFM) range hood and inadequate replenishment air, is that the hood will exhaust the air until the air pressure in the room drops enough to overcome the suction of the hood's blower, at which point it will simply stop extracting polluted air (you'll see smoke / grease "hang" in the air, instead of being drawn to the hood).

If you run into this symptom, this means there's a definite issue with make-up air. Open a window for a temporary fix, or consider using a make-up air (MUA) system for a permanent solution.

Answer 3

What about using the back of your fridge to preheat your make-up air? I had a mechanical consultant do that in an apartment building where the intake air was delivered to the gap behind the fridge..

Might be a nice (old-school) compromise..

Answer 4

We stayed for one week in a London 1-bedroom apartment hotel with a kitchenette. They had a HRV called Vent-axia built into the range hood, it kept the air super fresh (no windows could be opened) in the whole apartment, it also detected when we were cooking and you could hear the fan turning up.