You are buying a new water heater because of that? Reroute the pipes, install a fan, ventilate the attic, install attic floor insulation, etc. All of those things are cheaoer and have better payback.
We are already doing all the cheap stuff — bringing attic insulation up to R60 and sealing the attic to living holes (pipes, wood/wood junctions, wires, etc). We are also fixing inadequate attic ventilation problems - eave / soffit vents, rafter baffles/chutes, adding necessary ridge ventilation.
This is a 6 inch hole in the utility room dumping heat right to the attic. During winter, I measured the utility room temperature at 50F to 70F, so a lot of heat is flowing up that pipe. All the time the water heater is not firing, air is flowing to the attic. It’s actually a big heat load in the attic.
I’ve thought about alternatives (electric water heater; direct vent but no power fan; getting another source of combustion air to the utility room). None of these work for various reasons. The utility room floor is about 18 inches off the garage floor and it has a 10 foot ceiling, so I’m unable to tap combustion air off of the garage and still meet code (I talked to our local building inspector on this).
I keep coming back to a power direct vent water heater. Besides, the existing water heater is getting close to the end of its life. It is now 12 years old.