My Oil furnace and oil fired hot water heater connect and go out the one insulated chimney.<br /><br />I'm thinking not, ... but could a propane fireplace vent out the same chimney? or is two the limit...<br /><br />could an interface be made so the HWH doesn't come on while the f/p is on? I'm thinking a thermo-switch in the f/p pipe... don't suppose any of that would be to code though...