HVAC guys, questions for you.

I would like to know.

How big of an air conditioner would one need for a 1000 sq. house and a 2000 sq. foot house and so on, no basement, just a ranch. I am pretty sure that I have a 3 ton condenser unit, 2 pole 30 amp line going to it.

Also when a unit is listed as "tons of air" what does that mean, really.? In HVAC 101 class.

Ton of Refrigeration = 12,000 BTU/Hour.

There is a lot that goes into a detailed load calculation such as quantity/size/type of windows, direction they face, wall insulation, weight of wall, weight of floor, roof insulation, weight of roof, and I could go on for a while.

Having said all that..."MOST" residential applications will come out somewhere around 500 square feet/ton. Usually works better if a little under sized. So... 2000 SF=> ~4 ton.

As usual YMMV,

Kirk

Hello Gun Guru,
500 sq.ft. 1 ton or 12000 B.T.U.'s is right close. Also units are rated for the location that they are to operate. Higher humidity will reguire more btu's to condition a given space, less capacity is needed in a location with less humidity.
Guido

Here in North Carolina mountians "rule of Thumb" is 600 sq feet per ton. With that all you have is a rough guess. Kirk is right that you need a detailed load calculation with the new higher seer units. DH

Now I understand somewhat.

I have a 2300 sq foot home, with a 3 ton condenser, so it is undersize. But I have a lot of trees for shade. And the house is well insulated too. I wouldnt mind getting an additional wall unit for my bedroom.

And....the owner of my company is buying a building and it has 20,000 sq. feet of shop space. It has radiant heat and no air conditioning....That sucks. But I might be able to get to have an enclosed room for the machine shop. Shop supervisor may go for it, if not then I will get one of those small portable air conditioners that blows right on you.

its better to be slightly under sized than over capacity so you get dehumidification . with over capacity you will get a cold clammy house . dehumidification is as important as cooling for comfort.

The reference to ton is the approximate amount of cooling you would get if you had 1 ton of ice in the building. Just what i have heard.

Hello Guido. Gun hasn't said where he lives but I'll differ with you a little here. The higher the humidity the more you want it to run to get rid of the humidity. An air conditioner is really a dehumidifier so the more humidity the more you want it to run.

Where the rub comes in is that A/C's are sized for every half ton. 2 ton=24000 btu, 2 1/2 ton=30,000 btu, 3 ton=36000 btu and so on. In many places like here in KS, a 1000' to 1200' foot house could call for a 2.5 or 3 ton.

Then people get the idea that a 3 ton will cool quicker and save electricity by not running so long so the go for the bigger capacity. The problem is that the quick cool down doesn't get rid of the humidity and then your house is cold and unbearable.

Most HVAC pros I know and have read opt to go with the smaller unit and then expect it to run a high percentage of the day and night to get rid of the humidity in high humidity areas.

Now if Gun lives in the western mountains, they still use swamp coolers just to add a little humidity to the air.

Here in south central Ky it is 1 ton for every 500 sq ft. Had the local electric co-op come out and calculate our house bases on windows, porches, insulation bla, bla, bla., House is 2300 sq ft over a basement the same size. Their findings…. 1.5 ton for the house and a 1 ton for the basement. HVAC installer would not do it, said I had to sign a waver before he would screw something up like that by installing a very undersized unit. Called other HVAC installers and they said the same thing. I now have a 5 ton unit in the house and a 3 ton unit in the basement. I wish I had a 5 ton unit in the basement also as the 3 ton unit is a little undersized.

Bill is right here Gun. I don't know how much humidity you get off the lakes up there up there in Saginaw but 3 tons is probably enough.

Your problem probably lies in the distribution system. Maybe you can adjust registers, put dampners in the lines or set up a two stage system with electronic dampners in the lines. All expensive except for pinching off some of the registers to get more to the bedroom.

I would bet that the thermostat is by the living room so it shuts down before the bedroom gets cool. Pinching off registers may help there or you could move the thermostat.

It could be an issue with vent pipe sizing and if you are at the end of the run. Also before air can blow into a room, the return air vent has to take the old back to the a/c. Sometimes they undersize the return air vents to one stud cavity when it should be bigger and especially for big bedrooms at the end of the run. If leaving the door open helps then you have a flow problem.

One test the pros use is to place a kleenex over all the vents to compare how the blow. Then place a kleenex or tissue paper over the return and the suction should hold it in place (door closed). With multiple subcontractors around, I've heard of return vents installed in the wall but no one cut the stud plate and hole in the floor for the air to flow back.

More important than sizing the tonnage of the a/c unit for the house is sizing the plenum, outgoing, and return vents. They have to be sized so there is a pressure differential between the two and so each room vent carries the same volume. This is key to distribution and is hit and miss with alot of hvac techs.

On the other hand, if the bedroom is on the end of the run, your wife is having hot flashes from menapause, then get a small window unit so you can sleep comfortably and then you don't have to cool down the whole house as much may be the easiest way.

Get a 2 stage compresor and you will see lots of energy savings. My unit runs on 3 ton till it needs more then it kicks into the 5 ton stage for some serious heating and cooling. Same with my basement unit,they are both YORK units with variable speed air handlers, if that helps you any.

The amount of air that leaks through the house through cracks. Outside temp & humidity. Setpoint of inside stat and humidity.
Outside air temp and humidity.
Floor footage, is it a buried basement? Number of windows to the south and amount of shades?