I have gas heat and an AC unit. In the winter, I can set a 65 degree house to 70 and it heats up in about 15 minutes. In the summer, I can set a 70 degree house to 65 and it literally takes HOURS to cool down. Why the vast difference?

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Never underestimate the predictability of stupidity

heating is easy and very efficient. Just burn some gas or run current through a resistor, you get heat. You get even more heat if you use a heat pump, for every kWh used you can get more than 1kW of 'heat" depending on how cold it is outside and how efficient the heat pump is. IOW a heat pump is over 100% efficient.

Now the other way around, to take heat from the house and dump it outside where it is even hotter, that process is always less efficient, it can never be 100% efficient.

The furnace is probably oversized given that rate of heat increase. It is very common for fly by night HVAC contractors to oversize a furnace and not bother with the proper sizing calcs. It doesn't cost them anything and it ensures that they won't get call backs from cold customers. It also results in annoying short furnace cycles which will eventually kill the furnace.

Either the AC is undersized (or is broken...i.e. freon leak, etc) or you have an excessive heat gain problem, which could result from excessive south exposure windows with no low-e coating, lack of insulation, or too many heat sources (incandescent lamps, stove with pilot, etc) inside.

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"So be proud to be a decent American instead of just a w'anker whipping up fear!" - Michael D. Higgins, President of Ireland



Edited 3 time(s). Last edit at 03/13/2012 07:33PM by davester.

Also, make sure your coolant levels are good. If your coolant is low, it will take longer to cool the house down.

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Alpharetta, GA (Atlanta suburb)

Also, the BTUs your furnace puts out are almost certainly several times the amount of BTUs your AC can remove. With the AC, the compressor is doing ALL the work. With a furnace, the heat from combustion is doing most of the heating; the fan is just blowing that heat around.

Check the size of your cooling unit against the square footage of your house against where you live:
[www.acdirect.com]

Got fridge?
Got beer?
Got beer in fridge?
Then...
Got No Problem with AC!

Cold beer is well known to make up for most inefficiencies in any AC unit.
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I needed to check on proper sizing of a heat pump system when our church's package unit failed. I searched everywhere for free or very cheap software to do the calculations -- couldn't find anything that was reasonably effective and useful.

So I wrote two excel spreadsheets to do the calculations and annotated them, and made them available for download. People who have found them on my website tell me that they really help, especially as a check on what contractors recommend. They may help you to determine what's going on in your system.

Find them at: [www.moorepage.net]

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What it is, man, a low-down and funky feelin'

I guess I should check the AC Unit. The chart says I need a 2 ton unit. I have no idea what I have now. It sucks b/c the one side of house faces south...west I think. And there is zero shade on that side. And we have one window and a sliding glass door. So lots of glass. Sometimes it gets almost too hot to touch in the afternoons. We've tinted the windows on that side as well as hung some blackout curtains. There's just nothing else we can do...except suck it up.

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Never underestimate the predictability of stupidity

Awnings? Plant a nice shade tree?

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mikebw
Awnings? Plant a nice shade tree?

Heh. We live in a townhouse and an awning is against the rules. We've considered it though. And the living room (the worst part of the house) is on the second floor. So there is no place to put a tree.

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Never underestimate the predictability of stupidity

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bazookaman

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mikebw
Awnings? Plant a nice shade tree?

Heh. We live in a townhouse and an awning is against the rules. We've considered it though. And the living room (the worst part of the house) is on the second floor. So there is no place to put a tree.

Me too. These are things I thought would be good but can't really do either. I could plant a tree but it would take many years for it to help shade the house, a good investment in the future I suppose.

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bazookaman
I have gas heat and an AC unit. In the winter, I can set a 65 degree house to 70 and it heats up in about 15 minutes. In the summer, I can set a 70 degree house to 65 and it literally takes HOURS to cool down. Why the vast difference?

65 to 70 in minutes isn't terribly impressive if it is 85 outside.




If the AC is undersized or under-performing it must be costing more to run than getting it repaired or replaced, (long term) if hours to cool down is not an exaggeration.

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billb
If the AC is undersized or under-performing it must be costing more to run than getting it repaired or replaced, (long term) if hours to cool down is not an exaggeration.

Yesterday I got home around 5:15pm. AC was on. Inside temp was 73. Looked at it 15 minutes later and it was 74. So it was actually going UP while the air was on. Ate. Changed. Took little girl to soccer practice. Came back around 8ish. It was 72. And I'd imagine part of this cooling was the fact that the sun had finally gone down and it was cooling off outside as well. So yes. HOURS it is.

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Never underestimate the predictability of stupidity



Edited 1 time(s). Last edit at 03/14/2012 12:24PM by bazookaman.

Oh, I believe ya, but if that was your fridge there'd be something definitely wrong there, too.

That's gotta be costing you an arm and a leg to keep running with little effect like that.

When was the last time you had the AC serviced?

Also, I'm a little puzzled as to why you'd have the AC on if it was only 75 degrees.

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"So be proud to be a decent American instead of just a w'anker whipping up fear!" - Michael D. Higgins, President of Ireland



Edited 1 time(s). Last edit at 03/14/2012 01:16PM by davester.

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davester
When was the last time you had the AC serviced?

Also, I'm a little puzzled as to why you'd have the AC on if it was only 75 degrees.

We usually have it checked every year. Once we start using it. When it gets hot. Like AFTER winter. This year has been a little different.

And we use it when it's ONLY 75 degrees b/c myself and my daughter are very hot natured.

I love observations based on assumptions that everyone is (or should be) just like you.

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Never underestimate the predictability of stupidity



Edited 1 time(s). Last edit at 03/14/2012 01:36PM by bazookaman.

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bazookaman
And we use it when it's ONLY 75 degrees b/c myself and my daughter are very hot natured.

I love observations based on assumptions that everyone is (or should be) just like you.

Case in point? :ducks:

No, everybody is different, but I think we can all agree the unit is not doing the job either by failure in design or operation.

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bazookaman
We've tinted the windows on that side as well as hung some blackout curtains. There's just nothing else we can do...except suck it up.

Tinting only helps if you have had them tinted using a low-e film. A regular dark tint without low-e might actually make things worse.

Blackout curtains won't make things better. All that happens is that the heat is absorbed by the curtain instead of the floor, then radiates from the curtain into the room. The only way to stop heat gain through the window is to use a low-e film (to reflect the radiant heat back to the outside), and/or to use insulated glass (double-pane, preferably with argon fill) to stop conductive heat from heating up the inside of the glass.

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"So be proud to be a decent American instead of just a w'anker whipping up fear!" - Michael D. Higgins, President of Ireland