Tankless in an unconditioned NJ attic

boreing a-hole

dryer vents are 4 inches round and no one complains about them....

you want it to be faceing downwards towards the floor... no different than many closets with
a pipe from the attic going down to the floor for air...


A 50 power vent is probably a better choice...

the bradfords are energy star rated too...

I'm afraid I'd need a 150 gallon tank heater for my 215 gallon bathtub. I'm not even sure a tank would fit in that closet. What type of vent material would you use to draw air from the attic? PVC? Flexible aluminum vent? Rain gutters? Since this closet sits in an exterior corner directly beneath the entryway to the house, I would have to run 7 pieces of 3" round duct up an exterior wall to provide sufficient air. What would be the consequences of notching my bottom plate to that degree?

Actually, I guess I would need 7 vents since it's a vertical duct, correct?

Required free area of duct:
199,000 btu/4000 btu/in² ≈ 50 in²

Area of 3" duct cross-section:
1.5²*3.14 = 7.077 in²

Better check your math.

Nice catch! Thanks.

How about two 8" automatic intake dampers or a single 12" hooked up to the 24v system on my water heater? Maybe I should just try to sell this unit and buy a buy direct-vent model.