When RV heat is on, cabinets and counters get hot. Why?

Dear Dave,
The drawers and countertops in/on the cabinet that houses the heater for the camper get very warm when the RV heater runs. Is this normal or is there a blockage somewhere that is causing this? We leave the drawers open when the heater is on. —Jeff, Highland Ridge Open Range Light 275RLS

Dear Jeff,
When troubleshooting a furnace, it’s important to specify the temperature you are experiencing. I get the comment all the time that the roof air is not cooling, or the furnace is not hot enough, and we always need the temperatures to verify. (More on that after we walk through how the unit is designed to operate.)

You did not provide the year of your RV; however, looking at videos and brochures online, I believe you have a 15,000 BTU forced air furnace with remote vents. These vents are supplied with warm air by corrugated tubes weaving in and around lower cabinets, under the sofa, and sometimes even down through the basement compartments.

Diagnosing RV heat: Visual inspection

The first thing I would do is visually inspect any of the RV heating tubing you can find to make sure there are no cuts or tears, and that it is coming out of the furnace. There are typically two or more hoses coming out of the base of the furnace going to vents under the sofa and in a lower cabinet in the kitchen and bedroom. You can use an anemometer or air flow meter to check—this is the one I recommend.

This photo shows the one I used doing an airflow test on a roof air conditioner.

Check the air flow at all the vents. If there is one that is substantially lower than the others, it is not attached or it is blocked close to the furnace.

Cabinet should not have excessive heat

It is not normal for the cabinet to have excessive heat as there should be sufficient air flow from both inside and out. When the furnace starts up, the motor spins the fan, which pulls in cold return air from inside the rig, which passes over the burner assembly and goes out to the vents. The air passes over a sail switch, which is lifted and sends a signal to the module board that there is sufficient air flow to open the gas valve and light the burner. If the hose is just blocked, there would typically not be enough air flow to lift the switch and the burner would not light.

There is also a temperature switch at the end of the burner assembly that will shut the unit down if there is excess heat. If some of the vents are blocked, hot air will build up in the cabinet and shut it down. Also, the burner draws air from outside through the vent, through the inside of the burner assembly, and hot air is exhausted outside the exterior vent to help keep the cabinet cool.

I would suggest pulling out the drawers and using an infrared thermometer and test the actual temperature.

Having the actual RV heat temperature is very helpful if the unit is in warranty. You should then call the manufacturer and they should be able to tell you what is normal.

 You might also enjoy this from Dave 

RV ‘Gremlins’, Part 5: Forced air furnaces and why they’re so finicky

I typically don’t get as many questions about furnace efficiency as other appliances, mostly because of how people are using their units and how often the furnace actually gets used.

Most RVers store their rigs in the winter, so the furnace only gets used slightly when the temperature dips in the mountains or during autumn, so it doesn’t get tested as much in extreme conditions. Continue reading.

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

Read more from Dave here. 

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