Question about A/C

[sbj405]

I have it serviced every 6 months. The a/c unit is only a year old. It's been 100 degrees the last few days. The a/c basically runs non-stop when set at 75 (SO "must have" it set that low). Is this normal?

Other pertinent facts: one story house, 1000 sq ft, attic fan working, shaded yard.

[Longhorn]

1. My husband thinks there's something wrong but it's hard to know what.

The unit could be undersized. It may need to be recharged. Perhaps there are ducts opening into the attic. Perhaps the house needs more insulation. The bottom line is a properly sized unit with no other problems in the system should be able to cool a house to 75 degrees, even in 100-degree weather, without running all the time.

He's a remodeling contractor, by the way -- 30 years in the business. And we live in Central Texas where we have about a dozen 100-plus degree days per year.

[sbj405]

2. Thanks.

I got three estimates from reputable contractors and all sized for the same unit.
No ducts in the attic.
Insulation is good (per my home inspector and hvac contractors).

My SO thinks he knows the problem. Since the house existed for 55 years with no central a/c, there are no hot air returns. All the returns are low. One of the contractors suggested putting one in. Could you ask your husband whether one is essential? Thanks.

[Lisa0825]

4. I just got central AC this spring.

I am in the Houston area, and mine can't quite handle the heat either. In late afternoons on a hot sunny day, even if I keep it on 75, it gets up to 80 inside while running. But that's a hell of a lot better than what I was living with when I only had one window unit!

I do know my house has drafty windows and poor insulation though. Those projects are on my list for fall. I have to wait until it is cooler to add insulation because the attic is too hot to work in, and I just don't have the money for replacement windows right now.

What did you mean by "no ducts in the attic" though? Did you mean no ducts OPENING INTO the attic? Or is your air carried in a different manner than mine?

[TygrBright]

3. Nothing wrong with setting A/C on the low side...

...although airconditioned air for some reason sets my sinuses to aching, swelling, etc., and I just hate it generally. However, when we lived in a humid climate, it was always a trade-off between not sleeping because of the heat or not sleeping because of the A/C. Since the Darling Husband had no problem with A/C and suffered way more cruelly than I from heat, A/C won. But I would try to keep it as high as possible and still let him sleep/be comfortable.

A few weeks into the A/C season we noticed it was running all the time and yet not cooling the house. Whattheheck? we thought, and called the service person.

Keeping it set too high had caused it to actually freeze up and there was ice in the lines and all kinds of nasty problems, fortunately not too expensive to fix (We had to actually turn the HEAT on-- in July when it was 90-plus and humid, OY!.) But we learned our lesson. For A/C to work, it has to be set low enough for the unit to function efficiently. So having it set low (75 sounds chilly to me but my Darling Husband would probably sigh with bliss...) is not a problem unless it's not working properly.

helpfully,
Bright

[politicat]

5. What's the SEER rating, and is the attic fan ON?

Don't run the attic fan and the AC at the same time - you'll just be pulling outside hot air into the house and pushing the cooler, inside air out. Best time to run the attic fan is in the evenings when the outdoor temp is cooler than the inside temp.

Our 14 SEER AC runs about 35 minutes of every hour for about 5-7 minutes at a time. (It's cooling down from 90-100 to between 72 and 76, depending on time of day nad a bunch of other factors. Yes, I'm disgustingly low thermal. (But our electric bill is only about $35, so I'm not really unhappy.) ) It sometimes seems like it is on all the time, but I've actually wasted the hour to sit and time it and it cycles really quickly. Electronic thermostats will do that, since it is more efficient to maintain a temp than to cycle.

How's your insulation? Do you have blinds on your windows? What's near the thermostat (having a computer under the thermostat will make the thermostat kick the AC on a lot. Same with a stove or water heater.) Is the thermostat in direct light? Is there a light bulb near it? All of those things will make the AC come on a lot.

[sbj405]

7. It's an attic ventilation fan, not a whole house fan.

How is your bill only $35? Mine's about that in the months that I don't use A/C.

I got a new thermostat yesterday. We'll see if that helps any. It's not near any sources of heat and is out of the sunlight.

[politicat]

11. We're really efficient.

There are 4 incandescent bulbs in the house (the refrigerator, the freezer, the stove hood and the light on the through-the-door-water thingy). Everything else is low power CF or in a few cases, LEDs. We only use laptops, so we only use about 65 watts an hour rather than 300+. If it can be unplugged, it is unplugged unless we're using it. 14 SEER AC; it uses about 150 watts an hour. Highly efficient washing machine and I don't use the dryer in the summer (or whenever the weather's good enough to hang clothes out). We don't watch TV and rarely watch movies (on the computers sometimes, but not together) and keeping the house at a constant temp means that the freezer and fridge don't have to fight so hard to keep cool.

Next spring, we're going from an upright refrigerator to a chest fridge, and that will cut the fridge consumption to 36 kW a year.

And there are only two of us, and we both like darkness.

[sbj405]

6. A/c guy says the unit is fine.

Advice on how to convince my SO that cooling to 75 when it's 100 out takes awhile?

[Longhorn]

8. I haven't had a chance to ask my husband about the air return.

But I was wondering if you turn it off during the day? I understand it is more efficient to just set the thermostat higher when you're not there but not completely off or it will take forever to cool it back down. We have programmable thermostats for upstairs and downstairs. We keep it at 82 upstairs during the day and 78 at night when we're sleeping upstairs. We do the reverse downstairs, since no one sleeps down there any more (empty nest!) The first time we installed a programmable thermostat in a one-story home, the savings were noticeable -- it paid for itself in about four months!

[sbj405]

9. I set it at 80 during the day.

75 for the energy hog SO the rest of the time.

It's run for close to 2 hours and only cooled from 80 to 77.

[NMDemDist2]

10. you must have a huge leak in your duct system somewhere

this just isn't making sense

[sbj405]

12. How can I check that?

Basement is open so I have access.

Also, I have a supply vent in the basement. Should I close that? It's cool enough down there.

[NMDemDist2]

13. sure close that one and here's an article about duct leaks

http://rehabadvisor.pathnet.org/sp.asp?id=9709

edit to add, there are some more good links on the right of the page

[Longhorn]

14. Closing the basement vent.

I assume you mean that there is cooled air going into the basement. My husband says that if you close that vent and if that's the only air circulation down there, you run the risk of encountering mold and/or mildow problems. However, you could try it and see if it makes a difference. If it does, then maybe the answer is to find another way to air out the basement.

As far as checking for leaks, you may be able to feel along them to see if cold air is coming out. Or you can hire a professional who may use "powdered smoke" to visually see if air is escaping.

Fortunately, it sounds like your 100-plus days are over for awhile! :)

[Lithos]

15. Check your air flow

Could be that your vents are constructed so that the a/c dumps the air into the rooms closest to the unit, but not the last room where the thermostat is set and the air return pulls it back into the system before transient cool air makes it across.

If so, try constricting those vents closer to create anough back pressure so that the air makes it to the farthest rooms where the thermostat is. If the vents don't do the trick, they make magnetic covers for the vent to block them. Also, they make a weird variable pitch vent system which is a bit more sophisticated and is self-regulating.

L-