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I’m hoping to avoid the debate on the efficacy of attic fans, I have specific reasons for wanting/needing one so I’d like to avoid debating if they work.

I installed an attic fan in place of an existing air vent (and appropriately increased the size of the hole). It wasn’t until after I installed the vent (but not the electrical) that I read that you shouldn’t have attic exhaust fans in the same air space as gas appliance vents.

Our stove, gas insert, and furnace are all in completely separate parts of the house and vent outside, so I don’t think they’re a problem. What is a problem is our on demand gas water heater. The heater draws from the attic space and vents outside.

here’s the thing though, I’d already planned on having the fan blow INTO the attic. My understanding is that the risk with gas appliances is a back draft due to there being a negative pressure at the intake. In my case there’d be a slight positive pressure at the intake. I also believe there is a sensor in the water heater to protect against uneven pressures.

I can’t find any information anywhere on whether the hazard of gas appliances is specifically due to underpressure from an exhaust and if an air intake is safe. Does anyone know about this and whether it would be safe to install the fan blowing into the attic? I fully intend to ensure there is proper venting throughout the attic to reduce any over pressure.

I have read that it is allowed to add a cutoff to ensure the fan doesn’t run when the gas appliance is. I’m fairly confident I can do this if I have to, but I’d prefer not to if it’s not needed.