tons vs SEER rating

[mudbog]

i got the final of the 3 bids for an install of a new central air system. we don't have an existing system to replace so there isn't a previous configuration that can be considered.

with the 3 bids i got the following:

3 ton 11 SEER unit
4 ton 12 SEER unit
2 1/2 ton 14 SEER unit

what is the relationship between the ton and the SEER rating of a particular unit?

i'm guessing the ton is a result of the load calculation done. i'm surprised by such varied results. 2 1/2 - 4 ton seems like to be a big difference. is it?

thanks.

[NormChris]

There is no relationship between tonnage and SEER. Tonnage is cooling capacity and SEER is an efficiency rating.

Sort of like comparing the capacity of your automobile gas tank to miles per gallon. One gives you gasoline tank capacity and the other gives you efficiency in the use of each gallon. There is no relationship between the size of a gas tank and the mpg rating of the car.





[Edited by NormChris on 03-17-2005 at 11:50 PM]

[git-r-dun]

As Normchris said SEER is efficiency and ton is capacity, however to use his example, you will not need the same size fuel tank on a hybird in comparison to a Suv to go 300 miles. Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters. Ask them to do a heat load calc (Manual J).

[git-r-dun]

Sorry just wanted to simplify. A 80% efficient 3 ton (36000 BTU) unit will have an actual 28800 BTU output. A 3 ton 90% efficient unit would put out 32400 BTU, So more SEER the less rated input ton required

[mudbog]

is the heat load calc (Manual J) the method where the person measures the window sizes, where they face (North, South, etc.), how many vents, temperature reading (some laser gadget thing), etc. are taken. then results are entered into a computer software for the evaluation?

if that is it, only one of the 3 performed such test. they were the 2 1/2 ton 14 SEER bid.

one just looked at the information that the county assessor had on our house and came up with the 4 ton 12 SEER.

the other just interviewed me as 2 how many vents the house had, etc. and came up with 3 ton 11 SEER.

[mark beiser]

Originally posted by git-r-dun
Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters.

This is not correct at all.

The AC side of things doesn't work like the heating side. It isn't like gas furnaces where they are rating the % of the BTU input that makes it into the air. It is based on elecric usage, there is no correlation whatsoever between the capacity and the SEER rating.

A 4 ton 10 SEER system and a 4 ton 14 SEER system will have roughly the same cooling capacity, just the 14 SEER will use less electricity to do it.

A 3 ton 14 SEER system would have roughly 12,000 BTUs less cooling capacity than a 4 ton 10 SEER unit.

[beenthere]

Ask to see the load calc if they say they did one.
If they say they don't give them out till the contract is signed, then tell them that the calcs are to far apart, and you want to see who really did one, and who is guessing.

You can do your own, click the bulls eye at the top.

As most of the others said, seer means nothing towards capacity.

[Big]

Ask to see a heat load. Better on this site you can do it four forty dollars. SEER is to your A/C as gas mileage is to your car. Tonnage is amount.

[Shophound]

I can only add to what the others have said: click on the bull's eye at the top of this web page and download your own copy of HVAC-Calc Residential 4.0. This program is well written and will allow you to plug in the data for your own home to the best of your knowledge. You live in your home, you likely know it better than anyone (which rooms are hottest or coldest, how much insulation you have, etc.).

You can then take your results and compare them to any heat load calc done by a contractor (sounds like only one so far).

P.S. if you get a guy that comes out to give you an estimate and find him standing across the street on the curb, holding up fingers to see how many cover up your house to determine tonnage size, tell him with syrupy sweetness in your voice to have a nice day, don't call us, we'll call you.

[Gunnery Sergeant Hartman]

Originally posted by mudbog
is the heat load calc (Manual J) the method where the person measures the window sizes, where they face (North, South, etc.), how many vents, temperature reading (some laser gadget thing), etc. are taken. then results are entered into a computer software for the evaluation?

if that is it, only one of the 3 performed such test. they were the 2 1/2 ton 14 SEER bid.

This is your new contractor.
Congratulations!

[docholiday]

Originally posted by git-r-dun
Basically, what a 10 Seer 4 ton unit can put out in BTU, a smaller 3 ton 14 Seer (example) can do the same. It's BTU input rated but the output is what matters. Ask them to do a heat load calc (Manual J).

Sorry just wanted to simplify. A 80% efficient 3 ton (36000 BTU) unit will have an actual 28800 BTU output. A 3 ton 90% efficient unit would put out 32400 BTU, So more SEER the less rated input ton required

Where did you get this? Tell us you just made this up 'cause it sounded good.

[Shophound]

Where did you get this? Tell us you just made this up 'cause it sounded good.

I think the handle "git-r-dun" says it all.

[git-r-dun]

Thanks for the correction guys, I'm glad I atleast threw the manual J out there because that was pretty dumb. I guess my motto is what it is because quite honestly I did think ac was the same with heat as far as efficiency and output goes. Thanx again...