What type of caulk can I use between the furnace vent pipe & flashing on a roof?
I'd recommend Not using any petroleum-based sealant on any surface subject to heat (it will soften and melt). For a positive and weatherproof seal use any 100% silicone caulking (Dap, Owen-Corning, etc.). For an even better and longer lasting seal against water go with any exterior Urethane caulking. Well worth the slight cost increase, but is U.V resistant and stays pliable indefinetly. And there is no need for a high temperature rated sealer. Unless the area you are sealing is in close proximity to the heat source. Than you will need some type of refractory-type caulking.