Your building

The house has more than one heating or cooling system

“We have separate systems for upstairs and downstairs.”

Heating and cooling systems move air, and moving air changes pressure. Where a return is located, whether ducts run through unconditioned space, and how leaky the duct runs are all affect the pressure relationship between a building and the soil.

Multiple zones multiply those relationships, and they can work against each other in ways that are not obvious.

Why this matters

What it changes about the decision in front of you.

A return in a basement can depressurise that level relative to the soil, increasing entry.
Leaky supply ducts in a crawl space or basement can pressurise or depressurise the space depending on the leak location.

What it could influence

Where the effect is likely to show, and in which direction where that is knowable.

Which zones run and when will change readings over a day, which matters most for short tests.
A design may need to account for how the systems behave, particularly where a suction point is near a return.

What this does not settle

What still stands. Noticing a problem is not the same as losing the evidence.

Multiple systems are not a problem to be fixed for radon purposes; they are context for the measurement and the design.
Duct leakage is not a radon finding on its own.
It does not establish that the systems are causing an elevated reading.

What a professional is likely to ask

Worth having answers ready. None of these is a test you can fail.

Where the returns and supplies are on each level.
Whether ductwork runs through a crawl space, attic, or unconditioned area.
Whether the systems run on schedules or thermostats, and whether that changed during the test.

What you can check yourself

Things you can establish today, without anyone visiting.

How many systems there are and which areas they serve.
Where the return grilles are, particularly on the lowest level.
Whether ducts are visible in unconditioned space.

What genuinely needs somebody on site

Where this platform stops. These are not questions a website can answer about your house.

Whether the duct system is leaking and in which direction, which requires testing.
What pressure difference the systems actually create, which is measured rather than inferred.

Categories a next step could fall into

Unordered, and none of them is a recommendation. Which applies depends on things this page does not know about your situation.

Request a professional assessment

When it is considered. When the building itself is part of the question — foundation type, an existing system, access, or an unusual layout.

What it would establish. What the building is doing, which no amount of information typed into a website can establish.

Discuss another test

When it is considered. When the prior result is disputed, the conditions cannot be reconstructed, or a longer observation period would answer the question being asked.

What it would establish. A second reading under conditions someone can describe, which is what makes two numbers comparable rather than merely different.

Sources

U.S. EPA — Consumer’s Guide to Radon Reduction

When you are ready to talk to somebody

Tell us about your home and what you are trying to work out. We will tell you honestly whether we can route it to a provider in your area today.

Start a request