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Potential for Exhaust Fan in Residential Utility Room with LP Water Heater and Steam Boiler

How do I mitigate the faint "machine smell" in my house?

My house is 90 years old, and while it has been remodeled there are still aspects of it that seem it's in its golden years.

I have a medium-sized (8x15) utility room in my finished basement. I have a 2-year old steam boiler and water heater, both powered by gas. We installed a new exhaust system for both through a joint chimney with brand-new lining. Everything we have evaluated shows that these are exhausting well through the pipes and up the chimney.

There is a vented door that connects the room to the basement, potentially for air flow in(?). I also keep a small window near the ceiling open year-round and we have an air intake at the floor level.

My chosen life partner has a very sensitive attention to smell, one of her many wonderful attributes. However, the faint machine smell in the main level (~1,100 sq ft) sometimes bothers her enough to make me try to find a solution.

- Bad chimney: since we just redid this, I don't think it is it
- Replace door: this could work, but the drywall in the ceiling isn't fully sealed (pipes are exposed) so I think it could also just be coming up that way. Plus I am not sure the role the vented door plays in the overall airflow
- Exhaust fan: maybe, but I am not sure how it would affect the air intake into the room from the lower and upper vent, or combustion for the two units, or the natural flow up the chimney

I'm leaning toward exhaust fan as a new test, but wanted to get the experts to weigh in. I've had a couple HVAC contractors out that say "yeah I can add" but I am not sure they have the ventilation expertise. Wanted to get the pros here to weigh in.

This is the unit. You can see the ground level air vent. The vented door is right behind me. The ceiling level window is about 8 feet to the left.


  • Jamie Hall
    Jamie Hall Member Posts: 21,503
    A rough rule of thumb is that for every 1,000 BTUh of installed heating equipment you need 1 square inch of fresh air venting for the space. So the first step is to add up the BTUh of the boiler and the gas heater; that will give you the required area.

    The ground level air vent, if it is straight through, counts. Otherwise, if there is ducting or bends, it only sort of counts. The vent in the door is probably the main air intake for the space.

    If the appliances are draughting satisfactorily, then you do have enough. However, if you put an exhaust fan in there, you will not have enough any more. Probably not anything like enough, and you will have trouble with back draughting from both appliances. So don't do it.

    There is, however, a gadget call a "Fan in a can" which is intended to provide adequate combustion air. It goes through the outside wall like your vent, but is powered and interlocked with the appliances. To use it effectively, however, you will need to seal the utility room off from the rest of the house.

    So bottom line. You need that vented door or you can seal the space and use a fan in a can. What you CANNOT do is put in an exhaust fan.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 8,364
    You could try cleaning the new pipe first with paint thinner then with detergent and see if getting the oil off of it gets rid of your smell. Be careful because the paint thinner vapors are flammable.