I've got a basement that's around 1,000 square feet where my gas furnace and water heater are located. Lately, I've noticed that there's a constant airflow from the combustion air ducts, even when the furnace is off. It's strange because there aren't any exhaust fans running in the house. Is this normal? Also, I have a radon mitigation system installed in the sump pit, and while the slab is generally in good shape, there are some cracks. Could those cracks be causing my house to draw in unconditioned air through the ducts?
2 Answers
You’re right about the radon system; if it's constantly running, it's likely creating negative pressure in your basement, which can pull in air from the combustion ducts. The stack effect could also play a role as warmer air rises and seals off at vents on the upper floors. Unfortunately, if your setup needs that makeup air, fixing it might be tough without compromising your system’s efficiency.
It sounds like you might be dealing with a conventional furnace since you mentioned your furnace model is the Lennox ML180UH (which is an 80% efficiency model). These older systems often need proper ventilation, and having ducts directed outdoors for makeup air is common. The constant air flow could be a result of having to draw in unconditioned air to maintain combustion safety.
Got it. So it's pretty standard for regular furnaces then? That makes sense!
That’s disappointing to hear, but thanks for clarifying. I suspected the radon system was part of the issue.