Makeup Air for a Super-Tight House

 Our super-quite S&P Silent Series exhaust fan.

Our super-quite S&P Silent Series exhaust fan.

One thing I've noticed when staying at vacation home rentals is that they are often poorly ventilated. Bathrooms collect steam and feel damp all the time, the air seems stale in the bedrooms, and the exhaust hood over the stove is often ineffective or nonexistent.

When we set out to design and build Artemisia, we wanted it to be as air-tight as possible so we could meet our rigorous zero-energy goal, but we also wanted the air to feel fresh and the kitchen to be as functional and pleasant to work in as any home. We succeeded in our goal of an air-tight building envelope, meeting even the tough Passive House standard. We are also very pleased with how the kitchen exhaust fan system turned out.

Super quiet S&P Silent Series Exhaust Fan

The backbone of our kitchen exhaust system is a set of two powerful but quiet fans from S&P (Soler & Palau). S&P provided these units as part of our Artemisia Lab testing program, and Dave designed a clever system around them. The fans have a unique perforated inner skin, with sound-absorbing material behind it. Rubber gaskets on the inlet and outlet absorb vibration that would otherwise reverberate through the duct work.

Are S&P Silent Series fans worth the price?

At a retail price of about $175 per fan, these are no doubt a premium product. However, I have owned a cheaper exhaust fan in the past, and the difference is very noticeable. Whereas the S&Ps emit just a barely noticeable whoosh as the air passes through the grease trap of our Viking hood, my old fan emitted a low roar, like a mini jet engine spooling up for takeoff. It made it hard to talk during dinner parties. If you are someone who cares about all the little sounds emitted by the mechanical and electronic items in your home (which I am finding I am, especially as I get older), then it's probably worth springing for the S&Ps.

 We firred out this kitchen wall to make room for the makeup air vent behind the drywall. Ducting cannot be run in SIPs walls, and it really shouldn't be run in any exterior wall.

We firred out this kitchen wall to make room for the makeup air vent behind the drywall. Ducting cannot be run in SIPs walls, and it really shouldn't be run in any exterior wall.

What's makeup air, and how do I provide it?

Building code now requires you to provide makeup air for most range hoods. Makeup air is simply a supply of fresh air to make up for the stale air that your range hood is pushing outside. It can be brought in via a simple outside vent that opens automatically when you turn on your hood. Another solution is a powered system, like we have, in which one fan exhausts and one fan brings an equal amount of air in at the same time. Some people even go so far as to electrically heat the incoming air. We chose, instead, to direct it behind and beneath our range. We figured, if the hood is on, chances are the oven or stove will be, too, which will warm the incoming air a little.

 Case in point: As I sat here typing this article, the elk tostada I was cooking in the broiler started burning, and smoke poured out from the oven. I just flipped on the exhaust hood, and quickly and quietly, the smoke got sucked away. Voilà!

Case in point: As I sat here typing this article, the elk tostada I was cooking in the broiler started burning, and smoke poured out from the oven. I just flipped on the exhaust hood, and quickly and quietly, the smoke got sucked away. Voilà!

Some people advise owners of super-tight houses to pair a non-venting charcoal filter hood with a whole-house heat recovery ventilator (HRV) and eliminate the need for makeup air altogether. While we do have a robust HRV, we didn't like the idea of not having any way to exhaust smoke and cooking odors coming directly from the stove before they spread to the rest of the house.

How the exhaust system in our zero-energy house works

First of all, our exhaust system is completely separate from the HRV system that delivers fresh air to every room of the house. It is a self-contained system consisting of the two S&P Silent Series fans mounted inline on the ducts. The exhaust fan is ducted from our Viking range hood to the outside of the house. The other, which provides the makeup air, is ducted from the outside, behind the wall, and to the floor behind the range. We firred out the wall on that side of the kitchen so we could run this ductwork and inset the refrigerator slightly. The on/off and speed controls for the fans are integrated into the range hood. A separate switch next to the stove allows you to temporarily disable the makeup air fan if the windows are open, thereby saving a little bit of electricity.

 The inline fans for our kitchen exhaust system sit behind and next to the HRV, but they are a completely separate system.

The inline fans for our kitchen exhaust system sit behind and next to the HRV, but they are a completely separate system.

 Firring out the kitchen wall for the makeup air vent also allowed us to inset the refrigerator so the door is in line with the edge of the counter, almost like a countertop-depth appliance.

Firring out the kitchen wall for the makeup air vent also allowed us to inset the refrigerator so the door is in line with the edge of the counter, almost like a countertop-depth appliance.

 On/off and speed controls are integrated into the Viking range hood.

On/off and speed controls are integrated into the Viking range hood.

 This switch allows us to temporarily disable the makeup air supply to save energy when the windows are open.

This switch allows us to temporarily disable the makeup air supply to save energy when the windows are open.