I've just bought a house, custom built in 2006, Colorado.

The utility room has two 50-gallon gas hot water heaters in it, the room also houses fire sprinkler system with massive water vessel, well pump pressure tank, water softener, etc.

My issue is that the builder put in two huge combustion air vents to the outdoors, each 8" diameter (one high, one runs close to the floor). I understand that the hot water heaters need combustion air, but these large openings into my house are basically turning the utility room into the outdoors, so when it's freezing outside, it's @#$ cold inside, too. Thus the adjacent rooms in the basement are cold, as are the living spaces above the utility room.

Note that there is no insulation in the room other than on the exterior side, above the concrete slab wall in the space between that and the ceiling joists there's maybe 1-2 feet of fiberglass insulation. I've thought about adding 3/8" rigid foam to the concrete walls where I can (there's electrical boxes, plumbing, gas, etc. touching the concrete so it's not possible to add it uniformly) and I plan on insulating the interior walls with fiberglass insulation to help the adjacent rooms stay warmer.

But - this just doesn't seem right. I'm concerned about letting the room get so darned cold - that can't be good for the water softener, the hot water heaters, etc. It certainly isn't efficient to basically have the water heaters sitting in a room that could be 40 degrees in the winter (or colder?).

I've done some rudimentary calculations - There are 2 x 40,000 BTU water heaters in the utility room, which is 160 square feet, ten foot ceiling height = 1,600 cubic feet.

So my question is - given that this room is becoming a walk-in freezer all winter, how do you keep an outdoor vented space from becoming so cold? Two huge holes into my house is the opposite of efficiency and I'm seriously concerned about the heaters and softeners operating in potentially below-freezing conditions!

Thanks for your help. If you ultimately recommend I have a professional come out, I'd love a specific type of expert who would really know what the heck they're talking about. I feel like I certainly could have a local HVAC guy out to look at it but I would want someone who knows what they're talking about.