Living in airtight houses

Are We Designing Airtight Houses Properly?

Are We Designing Airtight Houses Properly?

Foreword by Ian Thompson, Editor

Today, Matt is addressing some challenges that can be found in many newly constructed airtight houses. He is shedding light on valuable insights worth understanding when designing your new house build or major renovation.

It’s notable that certain building codes and design principles advocate for airtight homes, some claiming it to be the ultimate approach for achieving building excellence. However, we need to be cautious in promoting this building philosophy alone, as there are other design and health factors we also need to address, namely the provission of adequate air replacement systems needed to replace lost air.

As we have discussed in previous posts, designing and constructing an airtight house can lead to numerous issues if not done properly, including controlling excessive moisture buildup. As Matt illustrates in his video, we have commonplace devices in our homes that are literally sucking the air out, leading to decreased air levels that can raise health concerns. I wonder if the councils pushing for airtight houses understand these concerns?

This video also revisits the topic of gas cooking. It emphasizes why we should contemplate transitioning to induction cooking, as it’s not only more energy-efficient but also healthier for the building’s occupants.

See this related video about gas and induction cooking:

Video Transcript

Hey guys, welcome back to my house. We’re not under construction anymore. In fact, I’ve just moved in and on the build show today, we’re talking kitchen ventilation. Now, when I say kitchen ventilation, most of the time you’re just thinking about this hood insert right here, and getting all those gases, those fumes, those smells, smoke from this cooktop area out of the house. But you know, there’s more to it than that, and we’re going to dive into some details today, including makeup air systems and two options for them: a passive system and a powered system. Today’s build show is sponsored by Fantech. Let’s get going.

Everybody’s got a smoke pen, right? So when we’re cooking, we want to make sure that the combustion gases, especially if you’re using a gas cooktop, are exhausted out of the house. Now, I happen to have a Miele induction cooktop here, so I’m not as worried about combustion gases, but I certainly want smells, smoke, and anything else that’s going to happen at this area to be exhausted out of the house.

A little example, here’s my smoke pen. When I turn that exhaust fan on, I’m going to be looking for that smoke to be going up the exhaust and out of the house. Now this is a particularly quiet system because I have a remote blower fan. This happens to be made by Fantech and this is an insert hood from Fantech. It’s connected with some ductwork and my remote blower fan is actually on the other side of the wall here.

So, walk around the corner in my pantry. This access panel right there, there’s the motor. That’s a 400 CFM Fantech fan, I believe that’s the Prio Air 400. But what I’ve done is at this stage in my house or at this moment, I should say, I’ve turned off my makeup air system. I actually have a very special makeup air system. It’s off right now and I’ve set up a little demonstration to show you what’s going to happen to my house, in particular, a tight new construction house, if I don’t have a makeup air system.

What I did was I put a piece of foam in this door between my laundry room and my garage and there’s an eight-inch hole in here that we’re going to open in a minute. And I have an eight-inch hole to the outside that’s connected to my fan, meaning I’m exhausting through an eight-inch hole.

Now, I use my manometer. Everybody has a manometer and a smoke pen, right? A manometer is basically a pressure gauge. See this red tube right here that’s going to the outside and it’s going to my gauge and the yellow tube is inside my house. This is a sensitive piece of equipment that’s telling me the pressure differentials between inside and outside.

Now with my makeup air off, you can see even with this vent taped up, there’s a little bit of air coming in and even with a tight house, my house, there’s some amount of leakage. I can’t seal it up a hundred percent perfectly, there’s always going to be a little bit of leakage and so that’s, you can see it’s blowing, it’s trying to suck the air in and then out that hood.

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But what’s interesting is you’re noticing my house has minus 25 pascals of pressure differential, negative, which means I’m really creating a vacuum in the house and as a result, all that air is trying to suck in and make up that vacuum. Now, that’s not good for us and it also doesn’t meet code. As of 2018, the International Residential Code has a new provision that says we need makeup air anytime we have a fan that’s 400 CFM or more and that makeup air needs to have less than three pascals of difference when it’s working between the inside and the outside.

Now that’s a safety thing, right? We want to make sure that our combustion appliances aren’t back drafting, that we’re not going to kill our occupants or have other issues. So let’s talk about makeup air solutions.

The first solution that I’ve used a lot and that a lot of people think of is simply to do a motorized damper inside the house with basically a hole. And here’s a Fantech option for you. And in fact, I have one of these as part of my makeup air system.

So what happens is when my exhaust fan turns on, there’s a relay to this that powers this and this power is open. And I’ve mocked this up right here in my garage. I need to open the iris a little bit and this is the same eight-inch hole, let’s say, as if I had a power damper. And now you can see that streamer is really rocking.

So, you would think an eight-inch exhaust pipe to the outside, all I would need to do is put an eight-inch hole in the envelope with the powered opener, powered damper, and I’d be good to go. Let’s go back to my pressure gauge. Let’s see where we’re at. Well, that’s not good, we’re at like minus 10 pascals. Ah, it’s going down a little bit, minus nine. Let’s see if it settles down. When I looked at it earlier and did this test before the video, it was averaging around eight to nine pascals of negative pressure.

So even that doesn’t meet code. It’s a little counter-intuitive but believe it or not, there are some tables you can consult to look at what size hole you would need but typically, it’s at least double if not triple the size hole if it’s passive that you’ve got pushing out, can attach to a fan. So for instance, if I were to put a passive system in, this eight inch is not enough. I’ve got negative pressure in the house. I probably would need something like a 16 or maybe even a 24-inch hole to let enough air in to suck it out.

Now on the other hand, what I’ve done here is I’ve done a powered solution and in my mind, this is the best solution for you. Fantech makes it, it’s really easy to install, and it’s very straightforward. Let me turn this system off and walk you through what we got.

Okay, now I’ve hooked up my powered Fantech makeup air system and I’m going to turn on my remote fan. It takes a second for it to ramp up and what’s cool about this is it’s nice and quiet because that fan is remote. It’s not right here above my cooktop and check that out, it’s going nicely. By the way, I’m sure you noticed, but I put the black trash bag up simply so you can see the smoke a little better. I do have a really nice tile backsplash from Clay Imports here but you couldn’t see the smoke very well with the white background.

Okay, so now that this is going and we’ve got the makeup air system going, let’s go take a look at what the manometer is doing for us.