Enclosing utility room (furnace / water heater) basement

Do NOT power-vent that room into living space. You never want to vent a room containing combustion devices into living spaces...as you state, that's asking for CO problems. It's not an issue of the furnace being defective, it's an issue of you sucking exhaust out of the normal path (the chimney) due to negative pressure.

You could get around this by using a direct vent/intake system where it becomes a completely closed circuit (furnace draws directly from outside).

I'm not an HVAC specialist, but a 90 degree room seems to me that there's something else amiss here...like maybe your circulating fan is underpowered?

Don't forget the combustion air is for all fuel burning appliances, not just the furnace. The water heater and possibly your clothes dryer also need combustion air. Yes, it is counter efficient, but not providing combustion air risks carbon monoxide poisoning. Not good!

One viable alternative would be to adequately heat the space, but that is certainly not efficient. It appears you could easily enclose the water heater and furnace in a utility closet. Be sure to determine the needed clearances and working access for each appliance and ensure they are maintained. AFAIK, the mechanical code often applicable in the US still requires two combustion air openings, one high and one low. You should verify your local requirements to ensure everything is correct. This is not the area to cut corners.

Even with the closet containing the cold air, if you have a gas clothes dryer, it still needs adequate combustion air. You would probably need some vents out of the closet to maintain this, but they can be relatively small, so the enclosure would still largely contain the cold air. Again, check your local requirements to determine the minimum vent area required for a dryer.

You would want to insulate the closet walls, and maybe even consider using an exterior door for access, as it will provide better insulation and weatherstripping to limit infiltration. OTOH, an undercut interior door might be adequate for dryer combustion air provision. You have a little research to do.