September 9th we closed on a home. I did notice a musty smell but we were told that it was from the house being closed up for the last two months since the owner passed away, we learned later that the house had a burst pipe and had been vacant much longer, all winter until mid June. I started searching and found black mold, cleaned that up but still smelled something similar to moldy wet towels/septic/radon pipe exhaust when the heat or air was on, so I had the ducts cleaned and the furnace tuned up. Still smells. I was just on the roof and the radon system pipe has a very similar smell to what we have when we turn on the heat or air,I'm wondering if there is any way that could be making its way when we turn on the heat or air? I know none of it makes sense but I've spent so much on mold guys and HVAC and everyone is as stumped as me and none of them can stand the smell in the house and we start feeling headaches, nausea, tightness in our chest, etc when we are in here which has made me and my dogs have to sleep in our pop up camper which just isn't an option anymore in WI as it's getting so cold. I'm desperate for any advice or thoughts on what this might be. Thank you so very much. Michelle

if the smell occurs when either the heat or the AC runs then you have to have a combined unit rather than a furnace for heat and separate ducts for AC?
need that info.

We have an ac unit outside and the oil furnace in the basement but they share the same duct work.



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Any chance the AC condensate drains to the sewer directly without a trap or the trap has dried up and when the heat turns on the positive pressure into the duct creates a negative pressure pulling the sewer gas from the condensate pipe into the duct work?

this is a picture form the internet that approximates what you have.


if you had a company out to clean your ducts, did they also clean the coils inside the furnace?

I don't think you are pulling in radon type air into your system.
unplug the radon fan so it won't pull any air from under the floor.
see if that does anything?

Also, I noticed that the vent for the furnace is close to where the radon pipe is, could the furnace vent be drawing in the smell from the radon pipe? Also, I called a radon place and they told me no smell should be coming out of that pipe and if it is we must have a problem under the basement. We're already $15k in debt from this "move in ready home" and all the issues they hid, I'm not even sure who to call now to figure this all out. :/

I'm not sure if the people that cleaned the ducts did that but we did have a HVAC guy and he cleaned the coils last Wednesday my dad said. Thank you for the tip on the fan, I'll definitely try that!

Oh man, I am so clueless to all of this. I'll show your message to my dad and see if he knows, thank you!



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"I noticed that the vent for the furnace is close to where the radon pipe is"..
try to explain just what the 'vent for the furnace' is ?

the air from beneath the floor (radon) is blown outside the house.
the heated or cooled air is air from inside the house that is circulated into the return air ducts by the blower and either heated or cooled then blown back out the supply ducts.

the only way you get outside air into your ductwork is to open a window or a door.

Disclaimer - I’m not a professional.

There are typically 2 separate air flows thru your system. There is the conditioned, house air, which circulates from inside your rooms into the return air grille (probably in a central hallway nearby to your thermostat), this air gets sucked by the fan thru an air filter and then thru your system, then up through the supply plenum (a big sheet metal box on top of your inside unit) and then thru the ductwork that supplies each room.

Separately, when the heat is on, there is combustion air that is sucked usually from the room where the unit is located, it is mixed with the fuel and burned, then that exhaust air/fumes gets routed up your chimney and outside your home.

The two air flows should never mix - the heat is transferred from the burning fuel air to the inside air deep inside your heater in something called the heat exchanger. It is possible these can crack and fumes from the burning fuel can mix with the inside air, this is a dangerous situation but typically manifests itself with increased carbon dioxide and carbon monoxide levels in the interior air leaving the unit. A profession hvac technician has the tools to measure the gas mix entering and leaving the unit to diagnosis this.

Anyway, the smell you describe sounds like dirty/moldy ductwork... the radon gas you mentioned doesn’t itself have a smell, but it is being pumped from the space underneath your house so it’s moist/humid and has that smell.

What is the humidity % inside your house with the unit running? It should be 30-40% I believe. Anything too high can encourage mold growth.

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..... We're already $15k in debt from this "move in ready home" and all the issues they hid, .....

? Was the home NOT "move in ready" ?

? Did you not move in ?

If they hid issues by NOT disclosing the KNOWN (or should have known) issues on the 'disclosure form' you have legal redress ... check with your closing attorney and/or the title insurance company.

? Do you have fire insurance ?

next time: CAVEAT EMPTOR

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