Yes, ASHRAE has standards based upon several factors. Some of the factors
1.) Insulation value of the building
2.) Max/Min ambient temps
3.) Max humidity
4.) Sun load
5.) Household heat load
6.) Desired air changes per hour
7.) Square/cubic footage
Bigger ain't necessarily better when it comes to HVAC.
Count the doorknobs and divided by 7. About as close as anyone's guess!
The only accurate way to know is to have a Manual J calc done. Other than
that, a very experienced HVAC tech can give you a WAG and get pretty close
I have seen 1600 square foot homes with 2 tons of AC that was to much, and
2200 square foot homes with 5 tons that was too small!
In response to Greg O 's post. I thought everyone should know:
your r-value and ceiling heights go into the factor too. i was shown how
to figure it out once when i was looking at house plans so i could use
that as a "HAVC cost guide" when considering the building plans.
i forget how it works but mike hit all the high points best i can remember.
stuff like ceiling trays and vaults go into the factors too. that would
fall under the cubic foot of air volume to be climate controlled.
Absolutely. It starts by calculating the heat gain. If you haven't been
doing it for 20+ years, you need to do the calculations. That means either
sitting down with paper, pencil, and Manual J, and figuring the heat gain,
or getting a computer program to do it for you. Put in too little cooling,
and it won't keep up with the heat gain. Put in too much, and it will drop
the temperature so quickly that the system doesn't have enough time to
HVACcalc (http://www.hvaccalc.com ) is a pretty nice program, and at $50 for
residential use, is pretty cheap. Try out the demo, and see what you think.
Ok let me ask this, not looking for an exact answer
1550 sq' single story 4 bed
12' celing in main rooms, 8 - 10' in rest
R-11 in the wall, R-24 in the ceiling
low e, dual pain windows, with additional window film to reduce as
much heat gain as possible.
3 ton unit
Does this sound ok? Mind you, I maybe a little off on some of the
above figure, but it is a 3 ton for sure.
It is probably the minimum that code in your area requires and costs less.
Less cost results in increased profit for the builder and higher bills for
you. Without going into complicated calculations, I would say that 3 ton is
about right for your area and size of your house. If you already have the
unit, what do you have to lose by installing it? I have a 2.5 ton gas pack
cooling and heating my first floor and will be upsizing it to a 3 ton SEER
13 or 15 myself either this fall or next spring. On 85 degree days, it
works just fine but on 92 and up days it runs for excessively long periods
of time (almost non-stop) and these $300 power bills are getting to be a bit
much. As Tom said, the real problem with over sizing is humidity control
but that might not be much of a problem where you live, especially if you
are near the desert. Here in NC, it is much more of an issue but 1/2 ton is
not going to reduce the run time excessively under normal days and will stop
it from running non-stop when it get hot. The bigger the house, the more
wiggle room you have with upsizing.
If at first you don't succeed, you're not cut out for skydiving
Long and the short of it is this.
Got this months elec bill and it was outrageous for a family that is
very energy wise. Talk to neighbors with homes by the same builder,
bills ran from 200 - 900 bucks.
All the single stories have the same make/model ac, two stories has
same make different model.
Homes by different builer on next block in same community have bills
that max out at 180!
Trying to figure out what the hell is going on. I know there can be a
lot of factors, but I have to start at group and work up
What is the SEER rating on your A/C unit? Do you have a lot of windows?
Any tint or treatments used during the heat of the day? Programmable
The SEER can make a big difference. For example, an 18 SEER A/C unit is
59% more efficient than a 8 SEER unit.
Different builders use different units. For example, in my last house,
my builder, Coventry, used Rheem 10 SEER units. The house next door was
built by Bradford. It had Trane 13 SEER units.
Sounds like you may have other things going on too ... like, many
windows. I put tint, 2" blinds and programmable therms in my last house
and it helped with the $400.00 per month bills those 10 SEER units were
According to the manufacture and the info I have on the unit it is a 3
ton, 13 seer.
Not a lot of windows but they are large, so that makes it about the
same. They are low-e rate, I have added additional low-e film to they
and am blocking about 75% of the incoming heat and uv. They have
window treatments over (2" blinds and curtains) them also, that stay
closed 90% of the time. (Remeber I am in AZ we have a lot of heat)
Like I said earlier we are VERY energy wise, all energy saving bulbs
that get used maybe an hour or two a day at night, gas vice elec dryer
and range, plus the window stuff mentioned above.
As of Jan. 1st 2006 A/C units manufactured after that date must be SEER
12 or above. I had my unit replaced last spring and was able to find a
SEER 10 unit to replace the existing 13 year old SEER 10 unit. Had I
gone with the newer higher SEER rated units I would have also had to
replace the exchanger up in the attic (I have a heat pump). That would
have been a major expense including cutting a hole in the side of the
house to remove and replace the exchanger along with the much higher
expense of the higher rated unit. Paybacks on lower bills would have
been too long for me.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.