How long should it take my house to cool down?

[SAWYER]

My a/c unit compressor went bad so I had it replaced today. I can feel cool air coming from the vents but it's taking forever to cool my house according to the temp on the thermostat. It was at 90+ and after 3-4 hours I am only down to about 80-82, is this normal?

 

[HappyPuppy]

It depends.

 

[mshan]

I would just wait till the new hvac gets your house down to usual temp you used to keep ac at, then see if the on off cycles are similar or better than what you were used to.

 

[Leros]

That depends on a lot of factors. I've seen houses take 30 minutes to cool and houses that take many hours.

 

[BoomerD]

I'm cheap with the A/C. I keep windows and doors open until it hits 81-82 in the house...then I turn on the A/C.

Takes about an hour to get to 77.

I live in a stucco house that's medium gray in color with dark charcoal tile roof. The attic hits 150+ easily on HOT days. That's a lot of heat mass for the A/C to deal with.

I keep talking about putting in gable fans to exhaust some of the heat...but haven't done it yet.

The hardwired models use enough electricity that they more-or-less negate the electrical savings of the A/C, the solar models are so expensive that it'll take a couple of years to pay back the initial cost, and they're not very efficient nor dependable.

 

[Rubycon]

Don't worry about how long it takes initially but instead take the temperature of the air coming out of the supply closest to the fan coil. Then take the temperature of the air going into the return. There should be a twenty degree difference.

 

[IronWing]

Usually the fire department keeps spraying water until the heat is reduced to the point they can get in to do an investigation. I'd still watch out for hot pockets under stuff that might have been shielded from the spray.

 

[GuitarDaddy]

Yep, depends on the size of the area, insulation value, and the tonnage of the unit. You stated that it brought down the temp 10 degrees in 3-4 hours which seems a little slow but probably just indicates the size of the unit is a little undersized for the space and heatload. If it eventually gets the temp back down in the comfort zone everything is good.

 

[SAWYER]

3 ton unit

 

[Rubycon]

Need more information...

90+ so was it 91 or 99? (or higher?!)

How big is the cooled space?

Is this a new installation, i.e. new indoor air handler/coil with new outdoor unit/condenser?

Remember if the return air is over 90 the supply will feel cool but not cold. Suction pressure will be high.

 

[boomerang]

Remember, if you've gone a while with the A/C not functioning in hot weather, there's more than the air in the house that has to be cooled down. The floors, walls, cabinets, dishes, the socks in your sock drawer, furniture, etc., etc., are all hot. Get the idea? You've got a lot of heat sinks in the house right now that are still radiating heat.

That much of a temperature drop in that amount of time under the circumstances sounds good to me.

 

[Vette73]

Don't worry about how long it takes initially but instead take the temperature of the air coming out of the supply closest to the fan coil. Then take the temperature of the air going into the return. There should be a twenty degree difference.

This.


If you have low/bad insualtion, old/leaky windows, or even old/bad duct work the AC has to work harder and will take more time.

What is the quality of your duct work? Is ti old and does it have any insulation?

 

[Jules ODwyer]

Depends on how Hot and how humid it is in the House.Say if house is 91 degrees and full of Latent Heat it could take 10 or more hours to pull down to say 79 degrees because it is working under extreme Load in the house .Latent Heat is very difficult and slow to remove but once done the other heat form is Sensible Heat which is numbers of degrees which is much easier to remove.Also if it's metering device is a Piston fixed Orifice or a Expansion Vale which Throttles the Refrigerant flow with opening forces and closing forces which is much faster pull down of house and more efficient form of cooling the house.Many factors attribute to cooling a space besides the norm as clean filters ,clean coil ,clean blower and correct speed of blower also clean condenser and proper amount of Refrigerant ,matched system to the proper size for space just to mention a few .

 

[Jules ODwyer]

3 ton unit

Just remember the Hotter the House even the correct size tonnage the Latent Heat in the house is high it may take hours to remove I have seen a house with 91 degrees take from hot part of day say 2:00 pm to run to 11:00 pm and brought down to only 80 degrees but by 2:00 or 3:00 am down to 75 degrees this is normal the Hotter and more humid in a structure the pulldown is hard and unit is struggling because it's not used to that type of load the Refrigerant is boiling off in your evaporator in the first couple of passes in coil but as it gradually keeps running the Refrigerant goes farther and farther in the evaporator coil before it boils off and most of the Latent Heat is removed the system then starts to remove Sensible heat which is a thermostat number game in sense of degrees of heat.Also remember at 90 degrees or more all the furniture ,rugs ,carpet wall etc has this extreme load that has to be cooked before you get cooked if that makes sense to you .Also if the unit brought your house down from 90 degrees to 80 in 2 or 3 hours your system is too large for the Space so just remember as long as you see the thermostat going down gradually overtime the system is probably working correctly as long as all the above mentioned system checks are in place.Remember let's say you like it at 75 degrees once the 90 to 75 is accomplished when it shuts off you are looking at cooling say 2 degrees it raises up comes on and starts Cooling from say 77 down to 75 this is normal that 2 degree pull down and shuts off

 

[Red Squirrel]

Considering just how hot it is that's probably normal. I find once it reaches a certain point it takes longer for it to start dropping more.

Also depends where you are measuring the temp. I have a split level house, you would not think 5 stairs would make a difference, but when I set the AC there can be as much as a 5 degree difference between main floor and "upstairs". Been wanting to look at zoning my main two trunks so I can have more air go on the upstairs part and I would just recirculate the air that would go downstairs back into the return. Just got to watch not to freeze the coil doing that.

I never really timed it but to go from say, 25C to 22C upstairs it usually takes at least a few hours for my house. Though if it's really hot what ends up happening is my main floor will be like 18 and my upstairs will still be like 23ish and won't seem to go down any more.

My hydro bill equal billing plan just shot up to $280/mo so I've started to be more conservative with how I use my A/C. Summer is almost over now and it's the end of season so probably won't really need the A/C much anymore anyway. Maybe run it for like an hour at night as I go to bed only.

One thing I've been toying with is getting a small window unit for my office, and maybe bedroom, and power them with my shed's solar setup. Essentially free cooling.

 

[BoomerD]

The thread was started 9 years ago, Jules...if it hasn't cooled down by now, I suspect a problem with the HVAC system...

 

[MtnMan]

One of the main thing the A/C has to do besides lower the temp, is to remove all the excess moisture from the air in the house, and that takes a while.

 

[Herr Kutz]

My a/c unit compressor went bad so I had it replaced today. I can feel cool air coming from the vents but it's taking forever to cool my house according to the temp on the thermostat. It was at 90+ and after 3-4 hours I am only down to about 80-82, is this normal?

My ac was out for several weeks and when they finally installed he new unit I’d say it took at least 12 hours to cool down. May have been more.