My upper floor and attic are too hot
3 September 2005
A.I donít know if this summer has been hotter than many in the past but all I know is I canít remember getting so many complaints about poorly balanced air-conditioning as I have this year.
My complaints about powered attic ventilators remains that they can fool you by pulling conditioned air from the house, from the upper level that will be replaced by cooler from the lower level, giving you the false impression that the fan is in fact ass isting in cooling. From a pure comfort sense you can argue that they are but at great and wasteful expense. My real complaint about attic fans, and a position from which I only reluctantly retreat and only under special circumstances, is that they have a reputation for burning up as they wear out and taking the roof-- and house-- with them as they blaze into oblivion. You could have someone over to the house in a hot day to examine the ceiling just under you attic with an infrared thermometer to see ju st how hot the drywall is radiating attic heat into the upper rooms. As for finding actual air leakage from the attic, that might be hard to do if you canít identify hot spots.
If you really think the attic is just too darn hot with what ventilation you now have consider adding passive roof vents along the rear face to reduce the obviousness of them. That should lower the attic temperature somewhat. Itís not uncommon to find air in attics-- ventilated-- at 140ļF. I entered an attic a few hot days ago that was an unvented hip roof with metal roofing that was above 160ļF. I didnít stay long.
You say you have about a foot of attic insulation. It really doesnít get much better than that. Iíll bet your thermostat for the heating and air is located about five feet off the floor of the first level. The thermostat is only sensing the temperature of the air just around it on the first floor. When that air gets to the set temperature it shuts the system off-- including the circulating fan. Try turning the little thermostat selector switch that says OFF ON AUTO to the ON position an leave it ther e for a day to see how the air temperature balance changes in the house. The fan will keep circulating the air throughout the house and will only turn on the cooling when the temperature rises above the set point. The desired result would be that the di fference between upper and lower level would about three degrees.
I have another reader who has reached the point where he feels the best solution is to install a separate zone of cooling for the second level. Expensive, but it would certainly give him greater control throughout all seasons especially if he uses a hea t pump. However the installer he consulted told him he would have to cut a hole in the side of his house to get the equipment in and he balked at the notion. My feeling is that there is another way into that attic-- it just hasnít been installed yet. H e would want an access from a bedroom or hall to the attic that an adult could enter upright to service the unit. His duct-work would have to be reworked and I told him without looking at it to think in the eight thousand dollar range by the time heís d one.
Along those lines:
Q. Jim, I'm in the middle of a bet with someone in my office (the boss). Our difference of opinion is about the increase in cost associated with the 13 SEER unit. In your article you said "Expect to pay almost double for a newer system by the time it's all done because the inside as well as the outside equipment will have to be replaced". Could you give me a brief idea of what the "inside equipment" that will have to be replaced is. P.S. This is serious as a cup of coffee is at stake!
A. I Donít know what side of the bet you are on but here goes. The inside equipment is the air handler-- consisting of fan controls, coils and auxiliary heating. And Iím sure youíll need a fancier thermostat. The new refrigerant, R410A, will not only req uire more coil area and more refrigerant to get the same Btu output as the older unit but will operate at higher pressures, twice that of R22. The old coils are incompatible and will have to be tossed. The new equipment will be larger requiring reworki ng of the ductwork at the connection. That may be tricky in many installations as the equipment had been shoe-horned into tight spaces-- requiring even more modification. Tack onto that the learning curve that the installers will be on getting used to all of the preceding plus the reality that the technical work-force is shrinking and youíve got a formula for high prices. The estimated cost increases put out by the industry are myopic and designed to mollify a trepid public-- especially for retrofits . New construction will bury the cost in overall house price. In my experience when an industry makes a guess on price increases of their goods or services, they low-ball by a factor of two, then explain away the turn-key costs as incidental and not thei r fault-- like all the modifications to accept the new stuff. Who gets the coffee?