Cool Down a Hot Attic
LESLIE: Up next is Ed from Tennessee who listens to The Money Pit on Discovery Radio Network. And you’ve got a hot attic. That’s a surprise. What can we do for?
ED: Yes. What happened was is that we needed a little extra room so I took an old walk-in attic area, I threw some walls up, put some drywall up then finished out the ceiling. And I’ve done the insulation in the wall but I’m still having some temperature problems with it.
TOM: Ed, is this room attached to your central air conditioning system by any chance?
ED: No it is not. I’ve got … what I did, I went out and bought a portable air conditioning unit that you duct to the wall somewhere. That’s what I’m filling it with.
TOM: Well, listen. When you’re going to refinish an attic and do a finished room, there’s a lot of considerations.
First of all, compared to any other room in your house, that attic room has more areas that are radiated by the sun than any other space in your house. Hence, the conventional rules of how big the air conditioner has to be just don’t apply. I mean, generally, with central air conditioning, you figure 600 to 800 square feet per ton. With a portable, you can kind of half that. You expect, you know, an air conditioner to do about half as much. But when you stick it in an attic and you have all of those surfaces that are being beat down by the heat all day long, sometimes even that is not enough.
Now that you’ve already finished the room, I’m not quite sure what else we can tell you to do. Had you called before you finished it, I would have kind of gone through a checklist with you of A – making sure that you had insulation in the walls; B – making sure you had insulation in the ceiling surface that you put across that ceiling, not in the roof rafters. If you had to put them in the roof rafters – such as if you had a cathedral ceiling – you would use about a third less insulation than you had space so that you would leave some space between the insulation and the underside of the roof sheeting for ventilation. Then we would have talked about putting in soffit vents at the roof overhang and ridge vents at the roof peaks so that you’re always washing air above that insulation, under that roof surface where you’re taking the heat out in the summer and the dampness out in the winter so you make it efficient.
But even after having done all of that, you still are going to find that you need more air conditioning than you probably expected. And in this case, I wonder whether or not the system you put in is a bit undersize because those were all the things on the checklist that I would advise you to look into to try to reduce the temperature of the room as much as possible, Ed.