RV furnace smells like rodent urine. Is there a filter to change?

Dear Dave,
We just purchased this RV and the furnace smells like rodent urine. Is there a filter for the furnace? How can I get rid of the smell? —Kathryn, 2003 National RV Dolphin 6320

Dear Kathryn,
Thank you for the question, as you have just added another smell to my dictionary of smells and noises found in RVs. I can say that I do not know what “rodent urine” smells like, but I can guarantee that I will not be doing a bench test on that!

The Dolphin was one of the best-selling Class A gas RVs in the market for several years. I did videos, product training, and marketing for National RV for a few years until they went out of business in November of 2007. The Class A Dolphin was reintroduced in 2006 as a totally re-engineered Class A that blurred the line between gas and diesel.

According to the online brochure, your Dolphin model 6320 is a Dolphin LX with a 35,000 BTU furnace. From the photos, it looks like the vents are incorporated into the cabinetry and not ducted underneath the floor. This means there are corrugated hoses running from the furnace to the vents.

The furnace draws interior air through the return air grate, which is typically located in the kitchen. This should have a very light filter to keep dust and dander from entering the furnace. However, I’ve learned to never say always (or never) when it comes to RVs.

Since you have a couch and dinette slideout on the driver side, I doubt it would be there. From the brochure photo of the kitchen, there is a large grate under the refrigerator that looks like it could be the return air. This makes sense, as the exterior photo shows the outside furnace cover directly under the refrigerator exterior access panel.

Where to start checking

I would start by removing the wooden frame of the interior return air and check to see if it has a filter. You can install one by fastening it to the inside. However, be very careful that it is a thin filter that does not block airflow. Otherwise, the furnace will not work as the limited airflow will not raise the sail switch.

If you have access to the furnace from under the refrigerator, check to see if you can disconnect the hoses from the housing. Clean out the furnace with a portable vacuum to ensure there are no dead rodents in there. You may also want to “snake” the vacuum hose into the furnace hoses to remove any dirt or other items, if possible.

It is very difficult to get odors out of the hoses as they weave through cabinetry and other furniture. I have been successful spraying Febreze in heavy doses in some of the hard-to-reach areas. If you cannot remove the hoses from the furnace housing, try spraying some into the air return with the furnace running so it will draw it in. Since the air is drawn in by the fan and flows over the burner assembly, the moisture should not do any damage to the inner workings of the furnace and might dissipate the smell.

Other options could be essential oils such as mints or air fresheners. If that doesn’t work, you might need to remove the furnace and give it a thorough cleaning inside and out.

Sometimes the metal in the burner assembly can get rusty or break down due to the extreme heat and gives off odors.

One last option you could try is an old trick my grandpa taught me. Smear a little lutefisk on the return air vent and you will wish the rodent urine was back!

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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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