Fabricating a Furnace Heat Exchanger, Hot or Cold rolled?

By mtmrico Date 10-03-2007 22:54

I own an older Yukon Oil/Wood furnace. It came with the house when I bought it along with an outdoor Gas boiler with baseboard heat. Since the gas boiler costs about $200 a month to run, I decided to tear into the Yukon oil/wood to find out why the previous owner installed the boiler. Turns out that the heat exchanger has huge rust holes in it and had been cheese balled before. The "POT" where the oil burner flame is blown into is also warped out of shape and consequently cracked in a few places. The cost for replacement parts is around $2300 plus shipping. So I decided to draw up some plans and have a local steel shop form the pieces I need to re-create the exchanger and the POT. According to the company, they originally went with 12 guage steel on the pot and 14 guage on the exchanger. And supposedly they used Hot rolled pickle & oil. Their new design uses 10 guage on the pot and the exchanger is now stainless. I've decided to go with the 10 guage steel on the pot and 13 guage steel on the exchanger. The steel shop I'm using has mostly cold rolled stock on hand. Does anyone know if the cold rolled would be a problem for this particular application. Any help would be greatly appreciated. Thanks, Mike.

By DaveBoyer (*****)

Date 10-04-2007 04:21

I will make a few comments as follows. I think the area where the burner gun flame impinges on should be firebrick, cast refractory or refractory board. This will promote clean complete combustion more quickly and allow the pot material to survive longer. If the cold rolled material is low enough carbon to weld without problems and soft enough for the required bends, I don't see a problem with it. The mild steel exchanger will have a limited life, I seem to remember CoreTen being used in similar aplications, and as You mention the new ones use stainless. The hot rolled pickled & oild material is probably more cost effective for the manufacturer than cold rolled, and welds and holds paint better than hot rolled with mill scale still on it.

By mtmrico Date 10-04-2007 19:30

Thanks for the reply. I just want to make sure the furnace stays safe for home use with the materials I intend to use. On a side note about the pot. There is a factory liner that needs to be installed before using the furnace. I believe it's 1/4 or 3/8 thick. Some sort of white heat shield material. Since I trashed the old one to remove it, I will be buying a new one. Thanks again.