Side vent clearance for tankless on demand WH?

I am adding a concrete block foundation around a small cottage in Palmer Massachusetts. Next summer, we will re do all the plumbing during a bathroom remodel and at that time, install a tankless on demand WH (probably a small Renai unit). This unit will be installed in the crawlspace under the bathroom.

Does anyone know what clearance requirements for side venting might be? I need to allow for this when installing the block and when planning for the unit next year, as headroom is limited.

I hope to just leave a 1/2 block space (8x8 inches) open and to run the vent through this opening and seal around the excess opening. I assume that these units are "sealed combustion" with incoming fresh air and exhaust venting through the same coaxial power vent pipe.

Also, how far from a window does this side vent need to be?

thanks,

See p.28 of the manual for the generic code clearances to doors & operable windows. (IIRC MA follows the standard US restrictions on those.)

The venting clearance requirements are specific to the venting terminal model used. Figure out which your using, see if the venting instructions for that version can be found online.

Local inspectors might take a different view, and adhere to the clearances for separately vented (not direct-vent), which can be found on p14 of the Takagi installation manual. (When in doubt...)