We're in the market for a new central a/c. We're in south Texas, in a
4-bedroom home, about 1800 sq. ft. living space, high ceilings in living
area, with a southwestern exposure. Needless to say, this house gets HOT,
and our old a/c just can't keep up.
My question is what size a/c unit should we get? I'm thinking a 4-ton, but
my stepdad says to get a 5-ton. Ok, even that large a unit would no doubt be
more cost efficient than the 20+ year old 3½-ton we have now, but do we
really need that big a unit? We will eventually be building a patio cover
and doing more landscaping near the house, but in the meantime we need to
cool this place off. Any suggestions will be greatly appreciated.
You need to get a reliable company to come in and do a Manual J on the
place. You can't just go by the square footage. There are so many variables
that have to do with sizing a unit properly. For example: I have a 2200 sq
ft house and a 2 1/2 ton unit does fine. My old house was 1700 sq ft and it
needed a 3 ton. (no I'm not in Texas, but I AM in the South).
Ask around and find out who the better contractors are and go from
How old is the old unit? It may very well be repairable. Does it cool at
The old unit is likely running way under efficient, so I'd be cautious about
upsizing by very much.
Of course, the way to go is to get a local HVAC company do a heat load
calculation and see how much you n eed. Or find a couple similar size houses
in your neighborhood. Go push the bell and ask what they use. Bring home
baked cookies when doing this.
Hi Stormin, hope you are having a nice day
On 03-Dec-04 At About 03:03:05, Stormin Mormon wrote to All
Subject: Re: Your advice on new a/c unit, please
SM> How old is the old unit? It may very well be repairable. Does it cool
SM> at all?
SM> The old unit is likely running way under efficient, so I'd be
SM> cautious about upsizing by very much.
SM> Of course, the way to go is to get a local HVAC company do a heat
SM> load calculation and see how much you n eed. Or find a couple similar
SM> size houses in your neighborhood. Go push the bell and ask what they
SM> use. Bring home baked cookies when doing this.
The only way is to get a manual J run on the house. asking a neighbor what
they use will not do any good as each house has it's own variables and needs
it's system custom designed.
.. It's all about Uncle Fester, isn't it? -- Wednesday Addams
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It should...whats wrong with it?
Unless you have never serviced it,or you have had hacks
like..well..sorrry..you stepdad..working on it .....
So wrong its not even funny
Are you trolling?
Real simple, and the ONLY way you will find out.
You get a licenced, competent contractor out there that will run what is
called a manual D, and J.
That will tell you the corrrect BTU rating (tons should be outlawed as a
form of description, since no two makes are the same) that you need for the
home, and not some wild assed guess that will cost you more long term.
No legitimate contractor will come out and install what YOU say to
install....he will install what you NEED.
As you know, it's very easy to find a contractor
that's willing to "sell by the ton".And with the more
being the better. Let someone say that they're distressed
with their current unit running 'most of the time', and they'll
quickly deliver one that's big enough to run an aircraft carrier.
The HVAC industry has done a dismal job of policing its
ranks, it is full of knuckle-dragging idiots that bring down the
profession, and insiders to the profession see it all the time.
Being licensed doesn't assure competance, but it certainly
helps narrow the field.
The way I learned it, a ton of AC is 12,000 btu, which in the "old days"
was about 1hp of compressor. This was in the late 70's, from a guy who
had been doing AC since the 30's, and I was helping out on 35 and 400
Now with more efficient units that "rule of thumb" on compressor power
is probably no longer valid, but the sales brochures on the units I've
been looking at match the 12,000 btu/h per ton measurement.
BTU/H is a standard measurement of heat movement. A 3 ton air
conditioner moves 36,000 BTU's of heat per hour. It is like a ton of
mass is 2,000 lbs (in English measure at least).
3 tons is easier to say than thirty six thousand British thermal units
per hour, but has the same meaning.
Nothing..he thought he was making a point ...
The only thing he pointed out was that after all those years working on ami
units, he knows that a ton, in AC terms is 12,000 BTU...
MY point was that 3 tons are not always 36,000...
2 tons is not always 24,000.....
Just because a unit is labeled as such, the total BTU rating can either
help, or hinder you.
From someone that worked on units that were sold by the BTU, its amazing he
didnt catch that.
Oh..that is another hint he wont get.
Yes. 3 tons is a single significant digit, which in this case would be
about plus or minus 3,000 BTU's. If you want a more accurate number,
more digits are needed, like 3.00 tons, or 35,900 BTU/h (3 sig figs).
For a 3 ton unit to not be 3tons it would have to be less than 33,000
BTU or more than 39,000, which is much different than 36,000.
If the calculations you are doing require more accuracy, than a more
accurate BTU number would be appropriate.
Thats not the point, altho a ton, as we know it, is 12,000 BTU.
A three ton Carrier is NOT the same as a three ton York, or Trane, or
Say you need a total of 25,000BTU's for a home...2 ton...right?
Buy one makes 2 ton,and you get 23,750 BTU...anothers, and 25,900.
Go to a higher SEER, and you change that all up...add another upgrade to the
air handler and you can change it dramatically.
THat was the point being made..units should be sold by the total BTU, not
the tonnage rounded off.
This is from a guy that works on York dryer units from time to time that
make 400 tons pale...and alot of resi stuff. Big deal what you worked
on....I fix, and advise on others work that have been doing it for years,
and claim to know it too..but when its done CORRECTLY, and thats more than
JUST the manual J, N, T, D or whatever is needed, but also the equipment is
matched to the wants, needs and requirements to the job, guess who wins out
Steve's got your back. He's right on. And in fact though, using the newest
figures you'll find that the newest most efficient units at standard
temperatures [ASHRAE 95º odt] the unit(s) aren't producing full capacity.
John Hines - you seem to be up to speed on what a ton of refrigeration is.
Can you tell me why it's [12,000 btu/h]called "a ton?" Funny concept but
"Steve@carolinabreezehvac" < email@example.com> wrote
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