Any suggestions, I'm putting a new roof (metal over shingles) on my shop which has a small propane heater and a 3.5" vent through the roof. Alternative is tear out the heater since I've not used it in the 3 years since we bought the place.
Missed this... did you find out what ya needed? Few options-- Silicone boot with sealing ring and proper caulk, or conventional roof jack (stainless is best).
Yes I was able to get an boot to fit, not entirely pleased with it but should do a great job keep the out the water, only concern I have is the very remote chance the double wall would get warmer than the boot is rated for. I'll monitor it if I start using the heater. Edit: the heater is only 12" or so wide and heating about 100 sqft
The red rubber boot is rated for high temp. Heck, regular silicone should handle normal operating temps. I bet you're fine. Is the 3.5" chimney stainless double wall? Or galvanized? Propane burners are clean (vs. wood) in terms of chimney build up. Most clearances (2" for a lot of double wall) are designed to take the extreme operating temp and not quickly transfer heat to combustibles in the event of higher temps due to chimney fire. They also prevent the heat from making combustibles more combustible (lol).
You mentioned the house being shingled... what was the existing flashing/boot? Did you use purlins or fir strips on top of the shingles?
It's my shop and I tore the shingles of, direct screwing into decking. Pipe is double wall galvanized. Origional one was galvanized with rain shield and tar like substance to seal shield to pipe. With the ridges on the tin that was not a good option. I used a stainless and silicone flexable boot.
