02 January 2011

Attic Fan

Favoured friends, Mr. Fuzzy spent much of a beautiful day in the dark attic, sigh, tackling a long overdue task: winterizing the attic fan.

For those of you not old enough to remember them, attic fans predate air conditioning. They are in the ceiling of the top floor of the house and suck hot air out of the house (if the windows are opened) and blow it into the attic and thence out of the attic vents, thereby cooling both the house and the attic, using far less energy than an air conditioner. Of course, it only works when the outside temperature drops below the interior temperature, i.e., at night. If there is little diurnal variation, it isn't helpful but here in the Blue Ridge mountain, it is useful on most summer nights.

The only evidence of an attic fan is the set of louvers in the ceiling. When the fan is activated, the louvers are opened by the immense flow of air. So now you know the theory of attic fans.

Now let me tell you about the one in the Fuzzy's home. When we first used it two summers ago, there were obvious issues: (1) the louvers only opened partially and (2) one louver stayed closed. I dismounted the metalwork and took a look inside - the problem was obvious - it had not been installed correctly (given this house, it that a surprise?). There was a cross brace in the ceiling opening and the installer simply disconnected the single louver that hit it. The group of louvers didn't open all the way because of a clearance problem, too. All I had to do was add and extra 3/4 inch of clearance from the ceiling by reframing the louver box and viola! They worked as designed for the first time, enabling an increase of perhaps 40% more air flow. Wow, what an improvement.

Now comes the next issue: those louvers form a very incomplete barrier to air flow when the fan isn't in use. In warm weather, no problem, In the winter, the cold air, being heavy, falls through the louvers. Worse, when there is a gust of air, it blows through the louvers, poring ice cold air into the upstairs hall. I am incredulous that two previous owners never bothered to make it air tight in the winter... I piled loose insulation over it last winter, a stop-gap measure, but now it was time to make a permanent solution to this heat robbing set up.

Mr. Fuzzy decided to build a box from rigid two inch foam insulation. No big deal, right? Four sides and a lid. Well, part of the problem is no place up there to stand and there are supports, wires, ducting and the large stove pipe which vents our heat system in the basement. The insulation is just deep enough to hide the joists that you need to stand on... or fall through the drywall. Then there is the problem of simply moving through all of the stuff... So the four sides were cut in the shop and then one at a time lifted into the attic to be glued to one another. It's difficult to stand on one small board and try to reach all the necessary places; balance is key. Oh, did I mention that there is no light up there? I had to rig a drop light and extension cord from the bedroom below to see... here is a view from the attic door.

Once the four sides were in place, which took more than an hour, then it was time to fabricate the well-fitted lid (if the lid didn't fit tightly, and the air could still infiltrate, then all was for naught). And here comes another problem. The aperture in the bedroom ceiling which leads to the attic almost seems to have been a post-construction afterthought. As amazing as that seems, the placement of the hole (in a bedroom) and strangely framed, seem to point to that. It also isn't very large... small enough, in fact, that although the pieces were cut in the shop, they couldn't be assembled in the shop. Instead they had to be passed up into the attic one at a time and then glued and finished while standing on one leg... the photograph shows the finished foam box before burying it with loose insulation.

The entire project was absolutely necessary and extremely frustrating. But its done and the house will be much warmer now.

2 comments:

Anonymous said...

Inspiring tale of DIY. I myself only realized the need to do this work after going to the trouble of insulating the attic access hatch door--which was a minor culprit compared to the whole house fan vents.

Staci said...

Attic fan is an integral part of proper ventilation in the entire house. Ignoring the issues of the attic fan might cause bigger problems in the future. Even if your HVAC system is running all day, but your attic fan is not working properly, it’ll still contribute to the poor ventilation in your home and it will only cause your energy bill to increase. So, it’s completely necessary to keep checking your attic fan, most especially during summer. Install gable, soffit, and roof vents, along with an attic fan for good air flow. ->Brooklyn Fan & Blower Sales Company