[Moneyguy1]

Which is a cautionary tale to put a garage gas heater "outside" the structure in its own enclosure, with only the returns and heated air return penetrating into the structure being heated. Eliminates the danger of explosive gases entering the heated space. Out here, without basements, the furnace and water heater are in a separate room, "sealed" (gasketed) from the living space, with a considerable amount of venting to the outside for any conbustible gases which may leak or CO which might not all go "up the pipe".