2 Speed Furnaces

[ganoga]

I am looking into a new heater. The house is about 4000 sq ft (2000 on top and 2000 on bottom). The house was built in about 1910 and originally had a gravity furnace.

A contractor told me that because the ducts in my house are located on the interior walls (typical for a gravity furnace) that a two speed furnace really wouldn't be very helpful. He said that two speed furnace are effective when the ducting is located on the exterior walls and the low speed can be used to keep the temperature constant.

Does this sound right? All the advantages of two speed furnaces sound compelling but I don't want to buy one if it won't work for my house.

[BobbyBJr]

Hmmmm....not sure. Around here we rarely see the supply vents on the inside walls, but still it does happen. We usually try to move them if possible. On the occasions it isn't feasible to move them, we have used them and gotten okay results, but not great. Usually cooling is more of a problem than heating, but with both the load is on the outside walls and that is the ideal place to put the supply vents. Discuss this further with your contractor. From just what you have said he does seem concerned to do you a good job. Many would just sell you the higher priced equipment whether you needed it or not. On the other hand, he might not be comfortable with the newer technologies yet and wants to avoid potential problems. I can't say for sure from here. Get another opinion from another contractor. I can really think of no reason a two speed furnace wouldn't work at least as well as a single speed, but in your application, neither is going to be fantastic because of the upper and lower zones and the placement of the vents. Really need to be there to say much more...

Bobby

[beenthere]

A 2 stage furnace will work fine with the supplies on the inside walls.

Any system would be better with them on the outside walls, including 2 stage.

With 2 stage you'll feel alittle more comfortable, since you won't get that sudden cold dratf feeling every time the furnace shuts off.

It does have to be set up properly, that means setting up the gas valve in both first and second stage, for proper heat rise.

Many contractors just turn on the switch, and say its works, thanks for your money and good bye.

[Black Adder]

I agree with beenthere, all 2 stage units must be checked for temp rise. Often people will complain that 1 stage heating is far too cool. Sometimes have to adjust gas pressure and fan speed to compensate. Back to the topic posted, a 2 stage will work just as well as a single stage in your application.

[docholiday]

why shoot yourself in the foot and use the exsisting ducts. You will end up with less comfort and not be happy. If ducting from the basement or crawl to the second floor is a problem then I would suggest 2 units, 1 for upstaris and 1 for down. The use of the exsisintg ducts is lazy and will be difficult to control.