i have searched on here and internet in general and cant seem to find an answer to my specific needs. a little background on home: located in new orleans (hot and humid), natural gas water heater in main living area, natural gas furnace in attic. im getting ready to spray foam my attic so it will be 100% sealed and all contractors say i need a fresh air intake for "cobustion" for the hvac unit. we rarely use the heater down here and when we do its usually very cold outside. wouldnt bringing in fresh air from outside make the heater work harder and vice versa. if it gets plumbed into the return air track then im bringing in 95 degree humid air and trying to cool it during the summer. this just doesnt sound right.
also does the air that the furnace is using to burn come through the return air also? i dont disagree with the contractors im just trying to understand. please help me understand how all this works. thanks