The house we’re renting has a “Florida room”: 90% windows and I can’t vouch for insulation in the roof/ceiling. And, get this — there are two AC vents and a large return in the ceiling. We have the door to the backyard open several times a day for K9s to relieve themselves and I keep hearing my Dad saying We’re not air conditioning the outdoors. It feels like we are. I closed the vents, but plenty cool air still escapes. The return really unnerves me; isn’t it sucking in 100 degree air as opposed to floor-level cooler air?
Yesterday, I cut some cardboard pieces to size and taped them in place over all three grills. The AC vents leak no more and the return is sealed (man, was it sucking air; it practically yanked the cardboard out of my hands and held it there while I taped it in place).
And, of course, the Voice of Doom is now harping at me that I’ve done something untoward to the AC system; even Googling couldn’t tell me if what I’ve done is not good (plenty of comments about adding another room would overwork the system, but nothing about closing off a “room”).
What say you, Dopers? Best case scenario, could we expect a drop in our electric bill? Thanks.
AC systems are designed for certain airflow amounts. If you limit the air through the system, problems can happen. One is that the coils can ice over. Without sufficient air flowing over the coils to warm up the freon, the coils will ice over from the humidity. Eventually the coils will be covered in a block of ice and air won’t flow through the system. It can even cause ice to form along the tubing to the coils. Another problem is stressing the blower motor. By making it harder to pull air into the system and out the vents, the motor has to work harder. Blocking the intake is like if you cover the opening of a vacuum cleaner hose and the motor gets louder. Closing the vents isn’t so bad. Covering the intake will likely lead to problems due to the amount of air that will be reduced.
What you might want to do instead is look for ways to reduce heat loss in that room. Do things like tint the windows, add insulation, plant trees that shade the room, etc. Another option is to get an HVAC company to move those vents somewhere else. That will keep the airflow the same without it going into that room.
If the Florida room is sealed off from the rest of the house and you sealed off both supply and return you should be good. However, you may want to find where the temperature sensor(s) for the thermostat are. If there’s one in the Florida room the AC will never shut off.