Look at it this way. A bigger furnace would simply mean bigger bills. 72F? I don't want to know what my bill will be if we try and keep thsi new home that warm I'm shooting for 68-70. But we'll see what happens when th humidty drops. Until i get all teh strom windows installed, my humiity levels will be limited... sicne the temperature of the single pane glass will determine hte maximum indoor depoint I can maintain.
You are correc,t Knowing your rate of infiltration is crucaial for a proper load calculation. You can try ot guestimate it. But only a "blwoer door test" done as part of an energy audit will give you an actual value. In some cases, air leaks can be responsible for most of the heating load... not conduction through walls and windows.
Start with air leaks in ceiling penetrations, then upstairs windows and finally downstairs windows and make sure you chimney damper is sealed good. Believe it or not, natural draft fireplaces can actually create enough draft that you'll cool off your home. that's why dampers are adjustable. Poeple tended ot use hte minimum damper setting back in the day, but that's not terribly safe and you get some of soot and smoke in the house.
Mostly I absolluately shocked that a clocal contractor didn't oversize you by at least 20-30%. I haven't found one yet that offered ot do a real load calculation. You may even be undersized because they used square footage. Old homes vary widely in infiltration.
IN my Home Borders install massively oversized furnaces in 2004. I have a 100k BTU downstairs and 80k BTU upstairs. there's ductwork that's sized barely adequately on both units. I'm added 2 supply registers just so the upstairs unit doesn't sound liek a jet engie is firing up (well it's not that bad, but it was pretty noisy). Also, no consideration for room size in how many and how large the registers were. They even put 2 supply registers in the attached garage !
Hello CO poisoning and gasoline fumes anyone?
I fixed that first thing. The PO's sadly were pretty ignorrant on HVAC.
In reality, I need a 80k BTU unit downstairs and a 40k BTU unit upstairs. A little smaller donwstairs if I didn't bother to heat the basement.
Honestly I'm not sure why they didn't just replace the boiler and install a single high velocity system for AC A single chase could have been run upstairs easily to the attic.... unless the boiler piping had a lot of leaks.