Two Open Doors to the Attic - A Building Science Nightmare
Take a look at this first photo. If you've got any building science training at all, I really don't need to say anymore. Sure, I could fill you in on some of the details, but I'm betting you already know that this is a building science and home performance abomination of the worst sort.
If you don't have any building science training, let me explain a little bit. I was standing in the attic of a condo yesterday when I took the photo of the top of this water heater. To the right of the water heater is a louvered door. That door opens into the hallway of the condo. On the wall just outside that louvered door is the thermostat.
In addition, the furnace and air conditioning system is also in that closet, with its own louvered door. The hole you see in the photo above is maybe only two-thirds of the whole thing.
- Air leakage - Air can freely move between the attic and the house. That means that conditioned air gets lost to the attic, and unconditioned air can get pulled down into the condo.
- Uninsulated walls (?) - In the photo above, you can see that the inside of the closet has sheathing, but the chances are good that there's no insulation there, as this condo was built in 1970.
- Thermostat confusion - With the thermostat so close to a huge thermal bypass, it may have difficulty making the whole condo comfortable, especially if the wall it's on is indeed uninsulated.
- Open, uninsulated ceiling - The top of the closet should be covered with a rigid sheathing material and insulated. A small uninsulated area can make a huge difference in conductive heat flow, as I discussed in my Flat or Lumpy article a while back.
The photo at right shows the view from the inside looking up. If you look carefully, you can see the roof trusses and roof deck up there. It looks like there may have been drywall over the top of the closet early on and then it got ripped out to make way for the ductwork that sits on top of the furnace and air conditioner. There's still a little bit there.
As evidence that this could be causing a lot of air leakage, I present to you Exhibit A, the louvered door. Notice the dust on the louvers and at the edge. The person who owns this condo keeps a very clean house, so it's certainly not from lack of cleaning that this happens.
What to do?
First of all, both the water heater and the furnace that live in that mechanical closet are combustion appliances. They also are both of the natural draft variety (furnace pictured below), which means that they need lots of air so as not to backdraft. Backdrafting means that air comes down the exhaust flue, which means that the exhaust gases aren't going up the flue, which means that the combustion process might be creating carbon monoxide and putting it in the house. NOT good!
So, one thing they could do here is lose the louvered doors and seal off all the pathways between the closet and the inside of the condo. Then you could put a ceiling on the closet with vents into the attic sized to bring in enough combustion air.
Better would be to replace the furnace and water heater with sealed combustion or direct vent models that bring in their own combustion air. In that scenario, you'd then want to go in and completely cover, seal, and insulate the top of that mechanical closet.
One thing that you don't want to do is just go up into the attic and seal the heck out of the top of that closet. It's not because you'll make the house too tight. The problem would be that you might leave the combustion appliances without enough air.
The building science principles are pretty simple here. You want a complete building envelope that's insulated and air-sealed. You want to make sure that your combustion equipment works properly. You have to do both of those things.
Building Science 101
Flat or Lumpy - How Would You Like Your Insulation?
Attic Stairs - A Mind-Blowing Hole in Your Building Envelope
An Incomplete Building Envelope Doesn't Work
3 Problems with Atmospheric Combustion Inside the Building Envelope
Making Your Home Safer with a Sealed Combustion Closet