*You would also need combustion air / exhaust air penetrations

Exhaust all avenues. 

Depending on if the hot water heater is gas or electric you may have to 1) run new gas lines and exhaust pipe to correctly vent the carbon monoxide. 2) run new electric to each hot water heater. because the additional electrical demand this would cause you may have to upgrade your service (circuit breaker panel). 

Is there an exhaust/ventilation system in the bathroom?

Some things that I have done in my home that I love and plan to use Keypad lock on front doorTimer for exhaust vent in bathroom - https://www.amazon.com/Enerlites-1-5-10-15-20-30-Minutes-Countdown-Decorator/dp/B00IB0ZJXE/ref=sr_1_1_sspa?

This just became my favorite thread.Put on your flame suit though.The F80 (the one you are referencing) is overall great, the only minus is the fart-can exhaust, and artificially pumped-in sound.

There should be vents under the soffit for air intake and vents on top of the roof for exhaust.

Researching other markets sounds exhausting.

When all efforts are exhausted on that front, another option is considered, like AP. 

Carbon fiber body panels, superchargers, headers and exhaust components, aftermarket wheels, performance pistons and rods, machine work, etc – these parts are not cheap, and the extensive modifications left my car absolutely useless during installations for long periods of time.In total, after spending $17,000 to buy the car that I eventually owned free and clear (excluding interest) and spending an additional $20,000 in performance and other upgrades to end up with a reliable 600hp beast on the streets, I was essentially going to realize a loss of $22,000 if I was able to sell the car for $15,000 - the current blue book value the day I stood in the garage pondering if I was ready to take the leap and sign it over to a buyer.