hvac sizing

[RSpermo]

The best way to size a HVAC system is to do the full manual J, S and D. Short cuts and other methgods can lead to mis-sizing.

[Charlie R]

I just don't think geothermal makes sense around here due to the installation cost, but a heat pump with gas furnace back up does. As you say, the average cold temp here in Maryland isn't really all that cold. JMHO

[John Dirks Jr]

Just found out the price I mentioned earlier does not include the AC unit and its only an 80% furnace. Now it's not interesting to me. I might have to continue to love my old system for a while longer, or at least shop around some more. Maybe I'll do the install myself.

[Jim Katen]

Just found out the price I mentioned earlier does not include the AC unit and its only an 80% furnace. Now it's not interesting to me. I might have to continue to love my old system for a while longer, or at least shop around some more. Maybe I'll do the install myself.

That makes sense. The price was too good to be true.

I'll bet that you could do the furnace install yourself, but the AC might be more challenge then it's worth. Do you have equipment to purge the system and charge it?

[John Dirks Jr]

Just found out the price I mentioned earlier does not include the AC unit and its only an 80% furnace. Now it's not interesting to me. I might have to continue to love my old system for a while longer, or at least shop around some more. Maybe I'll do the install myself.

That makes sense. The price was too good to be true.

I'll bet that you could do the furnace install yourself, but the AC might be more challenge then it's worth. Do you have equipment to purge the system and charge it?

I don't have the purging and charging equipment. I do have more than one friend in the HVAC business though. Maybe I'll talk to them about finding a good deal on equipment (appliances). I'll do what ever I can easily do, then pay them to come in and button it up.

[plummen]

You can pick up a vacuam pump and gauges on craigs list or any of those places pretty cheap,just make sure to buy the right gauges for the 410a systems []

[Robert E Lee]

I'd give the self install a go, I did that several years ago and then had an HVAC contractor come in to charge and set pressures. Got 30 years of use out of the unit (having a buddy in the trade is even better).

[blindrid]

The best way to size a HVAC system is to do the full manual J, S and D. Short cuts and other methgods can lead to mis-sizing.

100% correct, the one that I saw above that was used for the AC isn't worth the paper it would be printed on.

Use real Manual J at a minimum where you input wall sections, glass orientation - there is no short cut like the one used.

As to anyone guessing in here, without knowing the design parameters, any latent heat loads and other variables would be a worthless guess.

[Marc]

As to anyone guessing in here, without knowing the design parameters, any latent heat loads and other variables would be a worthless guess.

You must be fresh out of school. I've done hundreds of resid duct installs without doing the calcs. Every once in awhile when I had an unusual floor plan to duct, I'd ask my HVAC wholesaler to do the math on his computer just to check.

I suggested John D do the math because he doesn't do duct installs every day and because it's a good exercise for an HI.

Marc

[Bain]

Well, but if you've ever used Manual J and tried to apply its principles--and I have--you'll learn that it ultimately requires some subjective reasoning, and small amounts of guess-work and interjection-of-experience.

A baseline is necessary, I suppose, but don't for a minute think you can use Manual J, enter a bunch of values, and wind up with absolute figure for what a particular house or building needs.

[Tom Raymond]

Really, we need calcs and a baseline? Almost every house I looked at last year had a 100K BTU heating system. The age range was nearly a century with square footage from 900 to 2300. Pretty much 'one size fits all'.