Residential AC unit 1

[MotorCity]

I am currently taking quotes to have air conditioning installed in my house. It is approximately 1000 sqft single story and has a full basement and attic.

One of the contractors recommended a 2 1/2 ton Westinghouse unit. He also mentioned a "SEER" rating of 10. Does this sound appropriate or his he trying to sell me more than I need?

Also, do you have any recommendations or suggestions for a guy who knows nothing about hvac equipment and installation? Anything to look for or ask the contractor?

Thanks in advance.

 

[ClydeMule]

MotorCity,

That question can almost never be answered online. Even if you gave more information (like tons and tons more) it would be difficult to say.

If you live in an all glass house Phoenix, and have 20 webservers running in the living room it is probably on the small side.

You need to have your contractor do a load calculation and give it to you in writing. Call another contractor and have him do the same thing. Unless you want to piss off all of the contractors in town, don't say, " Joe Blow HVAC came guy and said I need this, is he full of crap?"

Just get a few different quotes. One thing I noted is that he quoted a 10 SEER unit, the cheapest unit and lowest SEER rating that legally can be sold. Either you told him you were being as cheap as possible, or he is selling you as cheap as possible trying to make a little margin.

Also, don't ask this question on alt.hvac unless you want to be ridiculed. Look around on hvac-talk.com, but don't ask questions unless you have a pile of information.

Luckily eng-tips.com is a professional and polite bunch.

Good Luck!

Clyde

 

[blutfort]

Clydemule is right, we'd need a lot more information to size it properly. A few tips...

1. If on the fence between two different sized units. Choose the smaller. I know this seems to fly in the face of everything else we do in engineering, but for home HVAC it makes sense. When you slightly undersize the unit it will have to run longer to bring the temperature down. That also means that it will be running longer and pulling humidity out of the air longer. Most residential applications you aren't trying to cool it enough to hang meat. Your family will probably be happier if the humidity is out of the air, than it the temperature is 72 instead of 76. Obviously ignore this post if you live in the desert or other low humidity area.

2.As far as the SEER goes, it's going to depend on how you use your air conditioner. I turn ours on in late May and don't turn it off until late september. Michigan can be pretty muggy and icky(Those are the technical words). I've got friends that only turn it on when it's unbearable. If you aren't going to run it a lot. Go cheep and get the low SEER. If your going to use it a lot look for a 12+ SEER machine. It will pay for itself in a few years.

3. Depending on where the condensing unit will sit in relation to your sleeping area should also impact your decision. I have a high efficient machine. This is typically done by over sizing the condenser coil and slowing down the condenser fan. I can barely hear the unit when I'm in the house right next to the unit. I've got friend that went with the cheep 10 SEER and they sound terrible.

4. Tongue in cheek way of sizing...Stand at the street with your arm in front of you. Close one eye. How many fingers it takes to cover your house is the number of tons to use for the condensing unit. (Crude, but close more often than not in modern subdivisions!)

5. When it comes right down to it, the brand name isn't going to matter much. I work for one of the biggies, but when it comes down to it they are commodities. Check the warranty. I know that a lot of the High Efficiency units come standard with 10 year compressor warranties. (I know ours do.)

Good Luck!

 

[MotorCity]

As you can probably see, I am a structural engineer who has absolutely no knowledge of HVAC (thank you all for pardoning my ignorance).

I realize that there are many factors that are involved in sizing an AC unit and did not expect to receive any definite answers in this forum. I am just looking to get some basic info and things to consider so I can have an intelligent conversation with prospective contractors. I do not plan to be in this house for more than 5 more years so I just wanted to have something reliable installed to up the resale value and cool the house in the meantime.

The impression that I got from one contractor is that a SEER rating of 10 was typical for a residence. Not sure what a SEER rating indicates, but I had no knowledge to argue the issue. If it makes a difference, the house is a one story bungalow style built in 1924 with aluminum siding and asphalt shingles.

blutfort -- You are correct about the humidity in Michigan during the summers! Without AC, itcan be very unpleasant at times.

For what its worth, I promise not to ridicule any HVAC engineers who ask "can I remove a column in my basement to accomodate my new pool table?"

 

[IRstuff]

Based on personal experience, most A/C guys will tend to over specify by about 1 ton per 2000 sq ft.

I went through a similar exercise about 4 yrs ago, half a dozen estimates all tried to sell me a 5-ton system for a 2200 sq ft house in the LA area. Only one recommended a 4-ton unit; we went with him and have been satisfied with the results.

TTFN

 

[blutfort]

Seasonal Energy Efficiency Ratio (SEER)
SEER is a measure of cooling efficiency for air conditioning products. The higher the SEER rating number, the more energy efficient the unit is.
New regulations will require units to be a SEER of 13 or higher starting in 2005 (I think).
Think of SEER the same way you think of MPG when you buy a car.

Are you saying I should have consulted someone before pulling out that metal thinggy to make room for the pool table? ;-)

 

[MarauderX]

You can ask your same question from installers here:

http://hvac-talk.com/vbb/

They will let also let you know what you need to under the 'residential' section.

 

[lilliput1]

If you divide 12 by SEER (or EER) you will get Kw/Ton power input
That is 12/SEER = Kw/Ton

At SEER = 10

Kw/ton = 12/10 = 1.2

At $0.13/kw and assuming 2000 equivalent full load hours per year and 2.5 ton capacity your annual electric cost to run your AC is = $0.13 x 2000 x 1.2 x 2.5 = $780

If SEER instead is 12 the kw/ton = 12/12 = 1.0

Your annual cost then is $0.13 x 2000 x 1.0 x 2.5 = $$650

Your annual saving w/ SEER 12 is therefore $130

If the SEER 12 unit cost $800 more, your years payback = 800/130 = 6.15. Decide if this payback rate is attractive. Note a typical AC unit will last 15 years but my LENNOX unit lasted 30 years! It was an energy hog though compared to the new units available now.