Ac q&a (how much, house, buy)

[Matchew78]

Ok folks I know it has been really HOT and humid out lately but for some reason I just can NOT keep my house at 72 degrees. I have my tstat set at 72 but stays around 77 to 78 all day long??? I measured my temp drop and I have 79.5 degrees at the return and 56.7 degrees at the register. Seems to me a little over a 20 degree drop is perfect from what I remember from my HVAC/R tech school I did in 2008. Granted I have just the schooling under my belt and do NOT work in the field do to the bad economy and Rets Tech over saturating the field with Techs and broken promises. But with that temp drop why am I not keeping my house cool??? Thanks for any input.

[Ohioan58]

How the heck should we know? Did you just notice this? What is the track record of your house's cooling over the years, or do you know?

The temp drop sounds good, but figuring what performance "should" be is still complicated. The compressor has to be sized to the house. I have been lectured by my AC guy that you really don't want an oversized central AC because this will result in short cycles and little improvement in the humidity. Ideally you want longer cycles with a smaller unit, which results in drying of the air.

Set up an appointment with a HVAC company to inspect your system and to take measurements like lineset pressure. That's the only way to know if it is performing correctly.

A data point: we just installed a high efficiency 16 SEER unit, 2 ton, for a 1400 SF house. The system will run pretty much continuously if it is sunny and above 90 outside and we have the inside temperature set below 75. And that's a new system. I find that the feeling of cooling has a lot to do with how much the unit is running and not so much with absolute temperature indoors. IE, if the temperature drops at night but is still muggy, the house will feel hot from humidity, yet at night the AC will not kick on much, with daytime temp settings. So at night I have to drop the temperature a little just so that the system runs enough to dry and circulate the air. So during the day I set the unit to 75-76, at night to 72-72.

But I have also lived with a system that had low charge, and it never gets cool at all.

We don't know what your problem may be. Check with a technician.

[dayton_ohio]

My guess is that you either have too small of a system for your house and/or very poorly insulated windows and doors.

Does the temp go down to 72 degrees on a cooler morning? If not, then you may be an issue with the thermometer/sensors.

I agree with Ohioan -- call a professional if it bothers you. Or buy fans.