A friend is planning to install a wood burning stove in his garage and has asked me if, during the winter when he fires up the stove with snow on the roof, will he get condensation dripping from the roof? The sloped roof is asphalt shingles on plywood sheathing with no insulation. He also has installed storage shelves on the rafter ties. I told him that I did not think he would get condensation as 1. the stove would not provide a large amount of heat and 2. the temp. gradient across the roof assembly would be small enough to prevent condensation. He wondered about insulating the roof at the underside of the rafters; I told him definitely NOT; but to insulate at the rafter tie level and to vent the attic space. Am I correct in my recommendations? Thanks to all.
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I don't see why, as a general rule, he would get condensation unless he is also doing something to add moisture to the air in the garage.
All the wood stove will do is heat cold dry air and turn it into warm dry air.
Now, if there is a large damp something in the garage, and it is heated enough that the heated air (which can hold more moisture) will absorb moisture from that damp thing (e.g., the slab) there could be a condensation concern.
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Just heating the air in the garage will not increase condensation on cold surfaces. In fact, heating the air increases the water vapor capacity of the air, so if you heat it without adding any moisture to it, it will actually reduce any condensation.
Some kinds of heaters, like unvented gas or kerosene heaters, would release water vapor into the garage, but a properly vented wood stove or non-combustion heater (like an electric or hot water radiator) would not directly affect the amount of moisture in the air.
The only way a vented or non-combustion heater would create condensation would be if it were heating open containers of water or stacks of very wet wood or something like that to increase the amount of water vabor in the interior air.
The real argument against wood stoves in garages is the risk of igniting flammable vapors. I think that risk can be managed, but some posters will disagree.
my experience leads me to believe that there would be no problem with condensation, but...depending on circumstances (how much/frequent snow, how frequent a stove fire, how consistantly cold outside) I believe he might end up with some spectacular ice dams along the eves....
Ice damming was my thought, but with infrequent fires for occasionally working in the garage, there shouldn't be much of a problem. Lots of places have similar situations. Just gotta make sure there are no gas fumes floating around in there.
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