Manual J Calculations for Residential house 1018 sq. ft. American Standard unit
Please help. My house is one story 1941, two bedroom, one bath. Exterior is stuccoand plaster. Old double hung windows, single pane, old roll insulation in attic. My house is in Whittier, California. I'm thinking of American Standard split unit 14 seer, 80% furnance, single stage. What do you think?
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There are a few variables that determine the size needed to cool your home - the size of your home, type insulation, are just two. I have a 2600 sq ft home - about 1300 sq ft per floor. I choose to cool the entire second floor (bedrooms and baths) and two of the largest rooms on the first floor (kitchen & living room) via flexible ducts from an air handler installed in my attic. My house was built in 1960, and at the time had electric heat. This means it is fully insulated. I replaced all the windows with energy efficient types, and vinyl sided. I installed soffit, ridge and gable vents to keep my attic well ventilated. I can cool my house in Boston, MA to 70 degrees (when it is 85 degrees inside) with a 4 ton unit in a little over an hour with no problem (one ton of cooling is equal to about 12,000 BTUs). Your condenser should not run non-stop. If it is not cooling then it is not a thermostat problem, but could be a gas charge problem. If you haven't paid the contractor in full yet - that may be the reason why. The contractor should know how much cooling you need for the space you have and installed a properly sized unit. Make sure your air filters on the return are clean and replaced regularly. Call the contractor and explain the problem - he should be able to solve it for you very quickly.
The AC your landlord installed is rated at 8000 btu which is way too small for 900 sq ft. You need at least a 15000 Btu Air conditioner and a 'well insulated' house to be cool.
A good rule of thumb in the AC business says you need 1 ton (12000 btu) of Air conditioning for every 600 sq feet (if the house is well insulated) - if not - then you will need 1 ton (12000 btu) for every 400 sq feet.
So, if you have 900 sq feet and the house is well insulated you should have at least a 15000 btu unit.
If it's not well insulated you will need 24,000 btu.
Assuming that there are ducts ran upstairs and downstairs, it all depends on the square footage of the living spaces, i.e. bedrooms, living room, dining room, etc. You need an average of 1 cfm per sq ft. For every 1 ton of air, you have an average of 400cfms. So your 5 ton unit will cool/heat 2000 sq ft. A 16 seer unit with a 95% furnace is a nice buy and you will notice the difference for sure. Hope this helps!
The answer that (TheMobilian) left couldn't be further from the truth, of offense. So you're saying if you have a 1000 sq ft house with 4 bedrooms you'd have 4.5 tons of cooling? That's insane, the compressor in that system would be shot in about 6 months from short cycling. Their are many factors in sizing equipment, but none of them involve how many bedrooms you have. If you don't know how to calculate load from windows and insulation factor, then you can use the old (1 ton per 500-550 sq ft) that will get you close.