Does Radon Come From a Furnace?
Does Radon Come from a Furnace?
No. A furnace doesn’t produce radon. Radon comes from the natural breakdown of uranium in soil and rock, and it enters homes mainly through the foundation. A furnace can affect how much radon gets into a house and where it ends up, though. Heating creates pressure differences that pull soil gas indoors, and a forced-air system can carry basement air to other floors. This article explains how furnaces and radon interact, how natural gas fits in, what to keep in mind when testing near heating equipment and what changes when a radon system is installed.
Where radon actually comes from
Radon is a radioactive gas that forms when uranium in soil and rock decays. It moves up through the ground and seeps into buildings through cracks in the slab, gaps around pipes, sump openings and other openings in the foundation. Because the source is the ground, the amount of radon in a home depends largely on the soil beneath it and how easily soil gas can get inside.
That’s why furnace rooms often read higher than upstairs rooms. They’re usually in the basement, the part of the house closest to the soil. The furnace itself isn’t the cause. A basement storage room with no equipment at all can test just as high.
How a furnace affects radon levels
A furnace doesn’t add radon, but it changes the air pressure in a house in ways that can draw more soil gas in. There are three main ways this happens.
Heating creates a stack effect
Warm air rises and leaks out through upper floors and the attic. Replacement air gets pulled in low in the house, including from the soil beneath the foundation. This stack effect is the main reason radon tends to run higher during the heating season. We cover it in detail in our article on why radon rises when you heat your house.
Combustion appliances use indoor air
Older furnaces, water heaters, fireplaces and clothes dryers that draw air from inside the house and send it outdoors all lower indoor pressure slightly. The Minnesota Department of Health describes this as a vacuum effect: as appliances and exhaust fans remove air, makeup air is drawn in, and some of it can come from the soil. Many newer high-efficiency furnaces pull combustion air through a dedicated pipe from outdoors, which reduces this effect.
Forced-air ducts move air between floors
A forced-air system pulls air through return ducts, heats or cools it and pushes it back out to every floor. If return ducts in a basement or crawl space have leaks or open panning, they can draw air from those spaces into the system. EPA technical guidance notes that central fans can create pressure differences that cause outdoor air and soil gas to enter at other locations. The system may also spread radon from a basement to upper floors, which can make upstairs levels somewhat closer to basement levels than they would otherwise be. How much this matters varies widely from house to house.
Does natural gas from a furnace contain radon?
Natural gas does carry small amounts of radon from the rock formations it’s drawn from. Studies of the gas supplied to homes have generally found that the radiation dose from this source is very small compared with radon that enters from soil. A Pennsylvania Department of Environmental Protection study of Marcellus Shale gas reached that conclusion, and an independent Carnegie Mellon analysis found that even the worst cases didn’t produce a meaningful added risk for typical household use.
A vented furnace also sends its combustion gases outdoors through a flue or exhaust pipe rather than into the living space. For most homes, natural gas isn’t a significant radon source. Soil gas entering through the foundation is the concern that testing and mitigation address.
Radon is not the same as carbon monoxide
People sometimes connect radon with furnaces because of carbon monoxide, which is a real furnace-related hazard. The two are different problems. Carbon monoxide comes from incomplete burning of fuel and can cause symptoms such as headaches, dizziness and nausea within hours. Radon comes from soil, causes no immediate symptoms and raises lung cancer risk through long-term exposure over many years.
A carbon monoxide alarm won’t detect radon, and a radon test won’t detect carbon monoxide. Homes with fuel-burning appliances benefit from working CO alarms and annual furnace maintenance. Radon requires its own test.
Testing for radon in a home with a furnace
You don’t need to change how you run your furnace before a radon test. Minnesota’s guidance tells homeowners to run their heating and air conditioning as they normally would. Short-term tests should run under closed-house conditions, meaning windows and exterior doors stay closed except for normal entry and exit for at least 12 hours before and during the test.
Placement matters more than the furnace’s operation. Put the test kit in the lowest lived-in level of the home, about 20 inches or more above the floor. Keep it away from drafts, heat sources, high humidity and exterior walls. That means keeping it out of the furnace closet and away from supply registers that blow directly on it. Our radon testing guide walks through the process, and our radon test kit comparison explains which devices suit a quick check or a longer, year-round measurement.
The EPA recommends fixing a home at or above 4 pCi/L and suggests considering action between 2 and 4 pCi/L. No level is considered completely safe. If your result is near the line, our article on what 4.0 pCi/L actually means explains how to interpret it and when a follow-up test makes sense.
Can you lower radon through the furnace?
Not reliably. Running the furnace fan continuously, sealing duct leaks or changing filters won’t fix elevated radon. A furnace filter doesn’t remove radon gas, and the gas keeps entering from the soil regardless of how the HVAC system runs. Sealing return ducts in a basement or crawl space can be a reasonable step for efficiency and may reduce how much basement air gets distributed, but it doesn’t stop radon at the source.
The EPA notes that ventilation-based approaches such as a heat recovery ventilator can help reduce radon in some homes, but they bring in more outdoor air and can raise heating and cooling costs. For most homes with a confirmed elevated level, the most common fix is active soil depressurization. This system uses a vent pipe and fan to draw radon from beneath the foundation and release it above the roof before it can enter the house. Sealing cracks helps the system work better, but sealing alone is usually not a dependable fix for significantly elevated radon.
What a radon system means for your furnace
Some radon mitigation methods change the air pressure around combustion appliances. The EPA’s Consumer’s Guide to Radon Reduction notes that a contractor may raise concerns about backdrafting, in which exhaust gases from a furnace or water heater flow back into the house instead of up the flue. EPA singles out crawl space depressurization as needing special attention to this issue. The guide says a contractor may recommend having appliances checked by a qualified inspector.
A qualified mitigation contractor should account for your furnace, water heater and any other fuel-burning appliances when designing the system. Ask how they’ll check for backdrafting, and make sure a post-mitigation radon test is part of the job. Our guide to hiring a certified radon mitigator and our radon contractor checklist list the questions worth asking. If your furnace or ducts are in a crawl space, our article on crawl space encapsulation and radon covers how those spaces are typically handled.
Frequently asked questions
Can a new furnace increase radon levels?
A new furnace doesn’t create radon, but replacing equipment can change how air moves through the house. Switching from an older furnace that draws indoor air to a sealed-combustion model may slightly reduce depressurization. Changes to ductwork or added exhaust can shift pressure the other way. If you’ve made major HVAC changes, retesting is a reasonable way to see whether your level moved.
Does running the furnace fan all the time lower radon?
It may even out radon levels between floors by mixing air, which can lower readings in the basement while raising them upstairs. It doesn’t remove radon from the house or stop it from entering. A confirmed elevated level is better addressed with a mitigation system that captures soil gas before it gets inside.
Do electric furnaces and heat pumps affect radon too?
Yes, though in a more limited way. Electric equipment doesn’t burn fuel, so it doesn’t draw combustion air from the house. Heating still drives the stack effect, and a forced-air heat pump moves air between floors the same way a gas furnace does. The heating method matters less than the soil beneath your home and how easily soil gas gets inside.
Should I put my radon test next to the furnace?
No. Heat and air movement around a furnace can affect the reading, and a furnace room may not represent the space where your household spends time. Place the test in the lowest lived-in level of the home, away from heat sources, drafts and exterior walls, and keep it there for the full test period.
Furnaces and radon in perspective
Your furnace isn’t the source of radon, and changing how you heat your home won’t solve a radon problem. What the furnace does is influence how strongly soil gas is pulled indoors and how it’s spread around the house, which is part of why the heating season is a good time to test. If you’d like to see what other homeowners have measured, you can browse radon readings reported near you. If your test comes back elevated, you can connect with a certified radon professional who can design a system that works with your heating equipment.
Sources and further reading
- U.S. Environmental Protection Agency, Consumer’s Guide to Radon Reduction (backdrafting, heat recovery ventilators, active soil depressurization).
- U.S. Environmental Protection Agency, Radon Reduction Techniques for Existing Detached Houses (forced-air fans, pressure differences, backdrafting).
- U.S. Environmental Protection Agency, A Citizen’s Guide to Radon (test placement, action levels, no known safe level).
- Minnesota Department of Health, Keeping You Safe from Radon (stack effect, vacuum effect from appliances, testing conditions).
- The Allegheny Front, Is the Natural Gas in Your Home Upping Your Radon Risk? (Pennsylvania DEP and Carnegie Mellon findings on radon in natural gas).
This article is for general educational purposes and is not medical advice. Long-term radon exposure causes lung cancer, but individual risk depends on the level, the length of exposure and smoking history. Reducing elevated radon lowers future exposure; it does not reverse exposure already received. If you suspect carbon monoxide exposure, leave the home and call emergency services. For help with your home, consult a certified radon professional or a qualified HVAC technician.
