Smoke On The Heater: What To Do If Your Oil Furnace Starts Smoking

Make sure to get annual maintenance on your HVAC systems to uphold your warranties.

Smoke On The Heater: What To Do If Your Oil Furnace Starts Smoking

Smoke On The Heater: What To Do If Your Oil Furnace Starts Smoking

17 February 2020
, Blog

Oil furnaces have numerous advantages over natural gas furnaces, propane heaters, and other home heating solutions, and many homeowners prize them for their reliability. Unfortunately, problems with oil furnaces can still occur, and one of the most alarming problems you may face is excessive smoke coming from your furnace's chimney.

The occasional wisp of smoke coming from your oil furnace is generally nothing to worry about, but thick grey, white, or black smoke billowing from your chimney can be caused by a wide variety of problems. Some of these problems are minor, but many of the more serious faults can lead to catastrophic (and expensive) furnace damage.

Why is my oil furnace producing so much smoke and how can it be fixed?

Dirty filters

The oil filters in your oil furnace are some of its most vital components, removing any impurities from the furnace's oil supply before it enters the combustion chamber. If your filters become clogged, these impurities will remain in the oil as it is burned, a common cause of excessive furnace smoke. If your furnace is making too much smoke, replace the oil filters or have them professional replaced.

Chimney clogs

Chimney clogs are another common cause of excessive furnace smoke. As your furnace burns oil, soot, and other combustion byproducts will inevitably build up around the interior surfaces of the chimney, as well as the flue pipes, nozzles, and end cones. This residue can block air flow and cause smoking if it gets too thick, but it can be cleared away relatively easily with a standard chimney brush or by professional furnace service contractors.

Wrong burner setting

Oil furnaces must burn at precise temperatures to produce the maximum amount of heat and the minimum amount of smoke. If your furnace is smoking excessively, it may be because its oil burner is burning at a temperature that is too hot or too cold. Adjust the burner yourself using instructions provided by the manufacturer or have it professionally adjusted to the correct setting.

Failed inspection door gaskets

If your home has a larger oil furnace fitted with an inspection door, it may be a hidden cause of your smoke problems. The inspection door is fitted with a gasket to keep it airtight when closed, but this gasket can warp and fail after prolonged used, causing excessive air flow and, consequently, excessive smoking. 

If your furnace's inspection door gasket is damaged, you can replace it yourself or have it replaced professionally. If you do tackle the job yourself, make sure to obtain the right gasket for your model of oil furnace, directly from the furnace manufacturer if necessary.

Improper chimney setup

In rare cases, an oil furnace may create too much smoke simply because it was fitted with the wrong chimney flue. If a chimney flue is too long and/or wide for the furnace, the exhaust gases and products it produces will cool down too quickly, producing thick smoke. Have your chimney inspected by furnace repair technicians to make sure it is suitable, and replace it with the proper chimney flue if necessary. 

About Me
It's More Important Than You Think

I used to routinely get calls from HVAC contractors in my area offering annual maintenance contracts. As soon they would identify themselves, I would quickly say no thank you and hang up. After all, my heating and cooling system was working fine. Why would I spend money on services I clearly didn't need? Boy was I wrong! A few years ago, my AC unit suddenly stopped working. I called my HVAC contractor to have it repaired and assumed that my warranty would pick up the bill. That was until I learned my warranty was voided due to a lack of maintenance. Out of nowhere, my decision to ignore those maintenance calls was about to cost me more than a $1,000. I know there are others out there like me. It is my hope that this site will provide them with the knowledge they need to avoid the mistakes I made.