Hello, My names Norm, I Live in Kalamzoo, Mich. and am new here.
I have recently purchased a house built in 1958 that is in need of a new system. It is a 3500 sq/ft two story with a partial basement modern style home with close to 100 single pane windows. It is a flat roof with good insulation. The walls that are not glass also have good insulation. The upper level is open on two side to the lower level. Forced air system with one large return in the basement under the open stairwell. It has two large outside air ducts (approx. 2 ft.dia.) one that goes directly to the furnace through a weighted damper and the other directly to the furnace room (this one has been closed off). 3 zones: all of main floor on one zone, upper level has one for master bedroom and one for the remainder. Originally it had an oil burner that was changed by the previous owner to gas. There is also a 5 ton connected.
I have had a couple of contractors out to evaluate and recommend. One wants to put two, 2 stage 80% variable speed amanas for the first floor, splitting the main level into two zones and then one furnace for the upstairs.
Others want to use one furnace with modulating dampers for zoning.
Opinions on multiple furnaces to single furnace? Aside from the maintenance costs being higher.
Have not done load calcs but the original system was designed by some guy out of NYC in '57 and here are his notes on the print:
Net heat loss 293,538 btu
pickup and duct loss 58,708 btu
total heat loss 352,246 btu
zone one 590cfm
zone two 1395cfm
zone three 3505cfm
design data outdoor -10
he spec'd a campbell model 200d 1/2hp blower originally.
There is now a 150k btu furnace being used. The house heats and cools fine but there are great temp swings between rooms, I would guess at least 10 degrees or more at times. Heating bills were 600usd at peak winter. (70degrees).