Converting Gravity Furnace to Forced Air

[abmiller25]

I am considering purchasing an older house (built in 1920) however am unsure about the heating system. It is an old furnace that uses gravity to heat the house (relying on the fact that heated, less dense air, will rise and cooler, more dense air, will fall). I'm aware that this is not an efficient way to heat a house and am curious to know how much it might cost to convert to a force air system. It's a 1500 sq ft two story house, and I'm assuming the majority of the cost will be to add ductwork but will I also need to buy a new furnance (one with a blower to move the heated air) or can I still use the existing furnace. Can anyone give me ball-park costs on how expensive a project like this might cost??

[Dean]

There are just so many variables and different ways to make it work just OK that it would be impossible to guess any ballpark figure.

I've seen people get by the cheapest way by just replacing the furnace only and the system worked OK but even that would depend on the cost of equipment, depending on what efficiency and which fuel etc. and what just has to be done such as asbestos removal or chimney liner installation, electrical circuits and on and on.

On the other hand a good quality job would be tare out and replace everything with new placement of supply and return air registers & grills and the highest efficiency equipment available which would cost a considerable amount more.

what you should probably do is get a few estimates from reputable contractors recommended by friends and relatives.

[HayZee518]

My mother's house had an old gravity type furnace fired by natural gas. There was a booster fan in the make-shift plenum above the furnace. Anyway this unit was replaced by a Williams forced air unit and retro-fitting the duct lines to the new unit wasn't difficult using 5 inch takeoffs to the existing ductwork. One joist space is used as the cold air return from two stud spaces first and second floor.

[imeduc]

Just how far do you want to go with this . We ued to put blowers on them all the time. take off the cold air drop. Put a blower to it in a box have filter fit the blower box tie the cold air right back into the blower box. Works like a top. To go all the way we took it all out . Use all the heat registers now as the new cold air returns. Then put new heat runs to just off the outside walls.

ED

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