Venting a condensing tankless heater

[MikeI]

I am planning on installing a Natural Gas Indoor Rheem Performance Platinum 90 condensing tankless water heater in my basement.

This is my first time working with a tankless heater.

My direct vent high efficiency furnace draws fresh air from a crawl space. I planned on doing the same thing with the water heater fresh air inlet (separate line of course). However, the installation manual says it must be fresh air inlet must be outside and that fresh air and exhaust should not be more than 24 inches a part.

I don't understand why having my intake and a exhaust follow different paths would be a problem.

I'm also not sure if getting fresh air from the crawl space is OK. This is what the furnace is doing. The crawl space has an outside vent, but I didn't plan on extending the pvc piping outside.

Is my plan OK or should I be concerned about something?

Thanks,
Mike

 

[havasu]

Sorry Mike, but we just dealt with another member asking questions on venting and gas appliances. This must be done by a professional on scene, not through the internet, and none of our professionals want to jeopardize the safety of your family by answering incorrectly.

For this reason, i am closing this thread.