Oil furnace backdrafting problem solved

Last winter, we occasionally smelled diesel near the oil furnace in the basement. We first thought there was something wrong with the furnace. We had our furnace guy checked it out twice and a power vac company sucked out all the gunk in the furnace. The problem persisted. We finally got some clues to the cause of the problem from the chimney guy. He checked everything including the furnace flue which looks just fine. He then concluded that the issue might be backdrafting. That seems to make a lot of sense. The diesel smell appeared mostly on Sundays when we cook and do laundry at the same time. The downdraft in the kitchen and the dryer are sucking a lot of air out of the house. While I was looking for a solution, we opened the kitchen window whenever we turned on the downdraft.

By this fall, I felt like we really need to get to the bottom of this. I called a local HVAC company. They sent someone out for an inspection. After explaining the problem, the guy brought in a manometer to measure the air pressure in the house. Here are the results:

  • Baseline (all appliances and furnace are off): -1.3 Pa
  • Furnace blower: -0.3 Pa
  • Bathroom exhaust fan: -0.5 Pa
  • Dryer vent: -1.25 Pa
  • Downdraft: -3.0 Pa
  • Sum of all appliances would depressurize the house past -5.0 Pa.

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