Preventing heat from hot water heater exhaust from increasing the temp in the room

You can use double walled pipe like this

If they are plastic, you idiot, they're don't get hot and won't heat up the basement.

I'm uncertain that the radiated heat from a modern water heater exhaust pipe is capable of radiating enough heat to raise the basement temperature by 5F, I suspect that the exhaust pipe is leaking somewhere, which is a much more dangerous proposition.

exhaust gets very hot and is certainly the culprit. Any ideas?

Install the water heater outside of the air conditioned space. In the garage is popular here but mine is completely outside the house in a purpose built structure next to the house. YMMV if you live somewhere that you pay for heat most of the year.

This may not be a "modern" water heater. Some of those old ones ran at efficiencies in the 70-80% when gas was almost too cheap to meter. Those stacks ran hot and you could use the top of the tank as a pizza warmer.

I'm curious why it matters. Would a thermostat controlled exhaust fan be practical? Covert to an electric water heater?

Yeah, that's real practical. It's in the basement and may already be in unfinished space. It would likely cost less and be easier to install a high efficiency direct vent. And what's the pay back compared to a bit of excess heat?

Still, it's not going to raise the temp of a basement by 5f, unless the "basement" is a 6x6 room.

Can a pizza warmer raise a basement by 5F?

On Mon, 2 Aug 2021 06:11:48 -0700 (PDT), trader_4 posted for all of us to digest...

I looked at HH for post followups and they stopped here so the OP will never see them.