Sizing heat pump with Man J

[jrongo]

I bought the home owner version of HVAC-Calc
Easy to use…learned a lot...

Numbers:
Sensible Heat Gain 31,652
Latent Heat Gain 3,422
Total Heat Gain 35,074
Total Heat Loss 87,087

The Company I chose wants to install a 4 ton heat pump. 4 Tons seems high for AC based on the math and maybe low for heating (not sure).

Is a 4 ton the right call? Should I ask the contractor to drop down to 3.5 tons to avoid humidity problems?

Thanks

[Daltex]

Did this company do a Man.J? If so, discuss with them as there are many factors that could have made their totals more than yours. Such as window shading. Did you use 0% window shading/covering (blinds/drapes)?

As for the heating aspect- list the heat pump model# and I know the brains on this board would be happy to give you the heating breakdown.

[jrongo]

Amana model ASZ140481A - I do not have a full coil number

I put no blinds on about 80% of the windows

This company did the man-j from outside. I am rather sure they used less detail than I did. They have not given me the man-J results. I have read that is not too uncommon as they do not want me to use their info to shop around. Fair I guess.

I am days away from putting up the down payment, waiting for US government to return my overpayment.

[Daltex]

I would get together with the salesman and go over your numbers with him. Ask him to go over your calcs. He may have just put in a fudge factor to get a quote that wouldn't have to go up if he got the job.

Doing an outside quick calc. has no way of evaluating your ductwork. Do you care if the new system is compatible with the existing ducting? Can't calc. that from the outside.

Don't know what your looking for but the fact that you have educated yourself enough to know to do a load calculation and the fact that you paid for HVAC-Calc leads me to believe you need someone who is better than your current company. Get more bids and I think you will find someone who knows more than you. I'd run the duct calc. if I were you and compare with current ducting. Then see if your quoted system is sized for your current ducting.

[MrMcGoo]

Heat pumps are normally sized based on the cooling load. However, it is accepted engineering practice to oversize the heat pump by up to 25% over the cooling load in cold climates.

The wild card is your summer humidity. If it is extremely high, then the 25% rule may cause trouble. If summer humidity is low, then the 25% rule may allow the heat pump to do 80% to 90% of the heating load.

Since air type heat pumps are from 2 to 4 times more effiecient than straight electric resistance heat, more use of the heat pump usually saves money.

Best strategy is based on fuel costs for various choices now and in the future and summer cooling needs regarding humidity removal.

Bill

[jrongo]

I think the 4 ton was based on the fact the old unit was a 4 ton.
I do not want to talk to another HVAC contractor. I am running out of them. I have spoken to so many of them.
On top of it all this compnay gave me a reasonable price.
If I can get away with a 3 or 3.5 ton rather than 4 I would want to do that.
I will call him when I get out of the office to get his take on the numbers.
Thanks again

[beenthere]

What is your OD design temp, and what is your ID design temp.

The load calc tells youo what capacity you need at those designs. Not what size unit will provide those capacities at those design temps.

At 95 OD temp, and 70 ID temp, you may need a 4 ton to meet your sensible load.

[jrongo]

outdoor - 89 summer 10 Winter
indoor - 76 summer 67 Winter

[jrongo]

What is your OD design temp, and what is your ID design temp.

The load calc tells youo what capacity you need at those designs. Not what size unit will provide those capacities at those design temps.

At 95 OD temp, and 70 ID temp, you may need a 4 ton to meet your sensible load.

That is the answer - I just ran with lower indoor temp and the tonnage jumped - thanks.