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rguerra · 07-04-2009, 10:41 PM

I have a 1400sqft home and need to know what ton I would need for AC. Also, my back room gets less air and is always hot. What could be or not be happenning?

Plumber101 · 07-04-2009, 10:50 PM

500 sq ft per ton close enough for 3 ton

However be careful you need to mke sure your existing duct work is sized for 3 tn both supply and return.

For example if you have now a 2.5 tn and want to increase in size need to double check.

For new install you can size as you go

AndrewF · 07-04-2009, 11:04 PM

Quote:

Originally Posted by rguerra

I have a 1400sqft home and need to know what ton I would need for AC. Also, my back room gets less air and is always hot. What could be or not be happenning?

There are a number of factors to the correct answer. The best accurate answer is to have a load J done.

To properly size the unit one needs to know the heat loss/gain of the house which varies by climate, home construction, etc.

For example: Single pane windows tend to lose and gain heat much easier than double pane.

You'll find varying answers without knowing the underlying data.

Likely to require more cooling capacity if this home is in FL vs Michigan.

**beenthere** · 07-05-2009, 08:11 AM

Do a load calc and don't guess or use a ROT.

I have 1650 sq ft, and am oversized with a 2.5 ton unit.
I could get away with a 1.5 ton.

If you have a room that is hot when you run your current A/C. Most likely its because your duct work is undersized.
Increasing A/C size doesn't help.

tinner73 · 07-05-2009, 11:14 AM

Quote:

Originally Posted by Plumber101

500 sq ft per ton close enough for 3 ton

However be careful you need to mke sure your existing duct work is sized for 3 tn both supply and return.

For example if you have now a 2.5 tn and want to increase in size need to double check.

For new install you can size as you go

you don't even know where he lives. how can you tell?

Florida or Minnesota? might be a different heat gain/loss.

manual J calc.

Yoyizit · 07-05-2009, 12:10 PM

http://www.degreedays.net/
Plug in your location and select Cooling Degree Days.

Is your hot back room facing SW?

rguerra · 07-05-2009, 02:40 PM

I live in south Texas and the back room is facing south, southwest. What would this mean.

Yoyizit · 07-05-2009, 03:00 PM

Quote:

Originally Posted by rguerra

I live in south Texas and the back room is facing south, southwest. What would this mean.

Probably that it needs its own window AC or
fan ('cause you have dry heat). I still have a motor from an evap. cooler I got while I was a "guest" of the USAF in San Antonio in the 70s.
Turns out there was a scorpion living in the motor windings. . .

**beenthere** · 07-05-2009, 04:35 PM

Quote:

Originally Posted by rguerra

I live in south Texas and the back room is facing south, southwest. What would this mean.

It means you should use the load calc program ink in post 4.

It means you could 2 tons, or 3.5 tons.

So do a load calc and find out for sure instead of guessing.

pomelo · 07-05-2009, 06:17 PM

How easy is it for a home owner to use that load calc program? Couldn't they make a mistake in the inputs and still be over or undersized?

Is it possible for two pro's to be off by a 1/2 ton in either direction?

**beenthere** · 07-05-2009, 06:45 PM

Its a very easy program for a home owner to use.
Plus, it lets you do what ifs.

What if you added insulation tothe attic, or installed new windows, etc. To see if you should make any other improvements decrease the size of equipment you need, and to lower your cooling and heating bill.

Its easy to make a mistake.
A home owner or pro could make a mistake.

but, you can look and review all the data you input into it. And double check how accurate you were.

Many times there will be a ½ ton difference between the load calc 2 pros/companies do.

Usually, the one that comes up with the smaller size is correct. And the one with the larger size, used a program that pads the size.

tinner73 · 07-05-2009, 08:09 PM

anything is possible do it yourself. if you get the wrong size you'll be sorry.

Gary_F · 07-05-2009, 10:26 PM

Some electric utilities will do a load test for free, call yours and find out.

psilliman001 · 07-08-2009, 09:16 PM

Quote:

Originally Posted by rguerra

I have a 1400sqft home and need to know what ton I would need for AC. Also, my back room gets less air and is always hot. What could be or not be happenning?

.......a favor & get a pro to run a load calc. on your house. no one here can do that properly sitting behind a computer . the ductwork , furnace , envelope , have all got to be evaluated so there are no surprizes at EXPENSIVE unit startups when it's too late. I know this is a diy site , but this part is definitely out of bounds for diy. Please err on the side of caution & get a pro as there are factors involved you may miss and then your family will be throwing darts at you when they're sweating all summer.....regards...............

Jack