I have been bouncing around thoughts between installing a wood furnace or an OWB. After a lot of consideration, I have about decided to go with the OWB and plumb it into my furnace fan and electric water heater. After realizing the output water temps on these units (150-180 °F +), I started wondering about ducting issues. My house was built in the late 1800's and the ducts are 6" round galvanized pipe under the house. Some of these have developing rust, holes, and other leaks. At 1 time, the ducts were insulated, but wife's cats have seeked out heat from them and decided to paw away at some of the insulation. Because of this, we are currently getting a blast of cold air when the furnace first comes on. This air is about 15°F colder than room air when it first comes on.
The crawlspace under the back end of the house is a real challenge. We also recently built on an upstairs addition, which will make it impossible to duct into the attic area. Because of this, I decided to install custom fabbed galvalume ducting on the lower level ceiling and then installing a drop ceiling under this. I just ordered the galvalume the other day and will pick it up Friday. This is actually 29 gauge metal roofing in 43" widths and 10' long that is still flat and has not been bent and shaped into ridged roofing. I should be able to curl it into round duct, rivet this together and get it to flatten slightly, if necessary. My furnace is a downdraft model which can be mounted in any direction. I will be pulling it up, sealing the cutout to the plenum under the floor, flipping it over, and fabricating a custom plenum to mount on the top and a heat exchanger to connect to my OWB, when I can get it before next winter.
Because of the temps involved with OWB's, I was wondering if I should have any worry about 150°F+ duct temps making contact with any of the structures and causing a hazard. I know from what I have been reading recently, the slinky style insulated flex duct is only rated to 160°F. I had first thought about using it in short lengths just to tie it together. Because of the temps, I am leaning more toward the metallic accordian type. Have any of you had to make any modifications to your ducting to prevent damages from the excessive heat? TIA
The crawlspace under the back end of the house is a real challenge. We also recently built on an upstairs addition, which will make it impossible to duct into the attic area. Because of this, I decided to install custom fabbed galvalume ducting on the lower level ceiling and then installing a drop ceiling under this. I just ordered the galvalume the other day and will pick it up Friday. This is actually 29 gauge metal roofing in 43" widths and 10' long that is still flat and has not been bent and shaped into ridged roofing. I should be able to curl it into round duct, rivet this together and get it to flatten slightly, if necessary. My furnace is a downdraft model which can be mounted in any direction. I will be pulling it up, sealing the cutout to the plenum under the floor, flipping it over, and fabricating a custom plenum to mount on the top and a heat exchanger to connect to my OWB, when I can get it before next winter.
Because of the temps involved with OWB's, I was wondering if I should have any worry about 150°F+ duct temps making contact with any of the structures and causing a hazard. I know from what I have been reading recently, the slinky style insulated flex duct is only rated to 160°F. I had first thought about using it in short lengths just to tie it together. Because of the temps, I am leaning more toward the metallic accordian type. Have any of you had to make any modifications to your ducting to prevent damages from the excessive heat? TIA