Return to the Heating & Air Conditioning Forum
| Post a Follow-Up
Manual J calc said I need half the size, is it correct?
| | |
Posted by shirl001 (My Page) on Wed, Nov 4, 09 at 12:03
| I just had Manual J did by the contractor and it came out half the size that was estimated by other contractor and my current units. The other contractor did not do load calc. I'm in Northern CA and the only thing I have changed in the 30 years old home is the double pane windows.
Original estimate:
Upstair, 1650 sq ft: 3.5 ton A/C 80,000 BTU
Downstair, 1550 sq. ft: 3 ton A/C, 60,000BTU
Manual J calc, base on 95 degrees and 30 degrees:
Upstair: 3 ton A/C, 27,000BTU
Downstair: 2 ton A/C, 25,000BTU
Are the Manual J calculation correct? It seems kind of low. The contractor said he used manual J and gave me just an excel results.
Thanks for everyone help.
Shirley |
Follow-Up Postings:
RE: Manual J calc said I need half the size, is it correct?
| | |
| shirl is the downstairs below or partially below grade? what was the inside design comfort temp for heating and cooling? I would want to see the Man J on the software's letterhead rather than an excel sheet. you can always run the Man J yourself for $49. Google HVAC Calc for homeowner version. see link below. If you have any hot/cold spots within your home, now is the time to discuss with dealer. IMO |
Here is a link that might be useful: Manual J Residential Software
RE: Manual J calc said I need half the size, is it correct?
| | |
| Shirl, My house in Central NJ is very similiar in size to yours. Here are my Manual J calculation numbers: Outdoor design temperature: 0 degree winter, 90 degree summer
Indoor design temperature: 72 degree winter, 75 degree summer Your calculated numbers seem reasonable for your area. How do they compare to your current systems? Upstairs: 1650 sq. ft 2.47 ton cooling, 45,000 BTU heating
Downstairs: 1550 sq. ft 1.74 ton cooling, 50,000 BTU heating |
RE: Manual J calc said I need half the size, is it correct?
| | |
| Currently, the system is 2.5 ton A/C and 60,000 BTU for top and bottom system. The current system is from original build of the home, 30yrs old. Thanks everyone for your valuable input. Shirley |
RE: Manual J calc said I need half the size, is it correct?
| | |
| How would you judge the existing system? Struggles to keep up? Cold and clammy? Runs way too much? |
RE: Manual J calc said I need half the size, is it correct?
| | |
| The heating is OK. The air condition takes a long time to get cool on a hot 90 degrees day and it runs constantly. |
RE: Manual J calc said I need half the size, is it correct?
| | |
| The best thing to do is get another quote, and when you call for the quote ask if they will or can do a manual j. It is too hard for us to give you advice on the size of equipment, there should be plenty of hvac contractors that are ready to help you locally with your A/C sizing. |
RE: Manual J calc said I need half the size, is it correct?
| | |
| The heating is OK. The air condition takes a long time to get cool on a hot 90 degrees day and it runs constantly. |
RE: Manual J calc said I need half the size, is it correct?
| | |
| That tells me you want to bump up the cool by at least 1/2 ton, not sure if you're talking upstairs or down. You certainly don't want to stay at 2.5 tons. |
Post a Follow-Up
Please Note: Only registered members are able to post messages to this forum. If you are a member, please log in. If you aren't yet a member, join now!
Return to the Heating & Air Conditioning Forum
|
|
|
