: My ventilation system is very similar. I have a sliding patio door
: at one end of my shop. I have cut a 2'x7' piece of rigid
: insulation to fit into the open door snugly. Within the
: insulation is a trap door that fits an evacuation fan. The whole
: unit goes in and out of the door in seconds. I just open a
: window on the other side of the room, turn on the fan and yes
: this keeps all dust, smells etc out of the house wonderfully.
: But when it's -10 outside, keeping the shop at 70 is impossible.
: 50 maybe. I try not to leave it on too long as the heating bill
: goes up quickly. I couldn't imagine leaving it on overnight as
: epoxy cures. I do run a small electric heater but it does not
: keep up with the frigid air rushing in. Maybe I just need a
: bigger make up heater.

Try leaving the window closed, and, if still necessary, using a smaller fan. The idea of my setup is not to move a lot of air through the shop, just to lower the pressure in the shop relative to the rest of the house. If the space is well sealed, the fan will actually move very little air out of the shop (or cold air in). I use an organic vapor respirator when I am in there with epoxy, so I don't care how strong the fumes are in the shop, I just want to prevent them from getting into the rest of the house.

I pre-heat the shop using both the small space heater and the furnace ducts, and then when I am ready to apply epoxy, I plug the furnace ducts with foam and let the space heater continue on its own. I can get the shop up to about 77F this way, and the space heater will keep it well over 70F overnight while the epoxy cures. The key is that the fans don't actually move a lot of air, they just reduce the pressure in the shop. Most of the air they do move comes from the rest of the house, not from outdoors, so keeping the space warm is not difficult.

Best regards,

Allan Edie