Dear Dave,
Is there an air filter on a fifth wheel’s gas furnace? If not, should one be installed? —Gary
Dear Gary,
Yesterday, I posted a question from a reader on how “hot” his furnace was operating. I thought this would be a good follow-up to that post.
In a residential HVAC setting, your furnace does have a filter in-line with the cold air return. The blower is typically used for both the furnace and air conditioner. The only RV HVAC system I know of that has a residential filter is the TrueAir system developed by Winnebago back in the 1990s. It had a two-ton compressor in the basement compartment with a filter in under the bed in the Vectra for a couple of years. However, that only filtered air for the air conditioner and heat pump option, not the furnace.
The RV’s furnace system
Typically, the furnace in an RV is mounted in a hard-to-reach enclosed cabinet with an exterior intake and exhaust vent.
When the thermostat calls for heat, the blower motor starts and draws outside air from the vent and purges the burner assembly or air chamber and exhausts it outside. This is a closed system so no outside air enters the rig and does not need to be filtered. At the same time, interior air is drawn in through the air return vent or vents and flows over the burner assembly and lifts the sail switch to provide a closed circuit. Here is a photo of the air return in a 2005 Winnebago Brave which is the brown vented grate on the back wall. The white vent on the floor is the heat register.
At that time the module board then opens the gas valve and provides spark, which lights the burner and provides a heat source.
So do RV furnaces have filters?
Because of the compact design and confined space, I do not know of any Original Equipment Manufacturer (OEM) such as Suburban or Hydroflame that is using a filter at the return air vent or the return air opening on the unit. Most RV manufacturers will not modify the installation recommendations of the OEM, so I have not seen filters as of yet. However, I have learned to never say “never” when it comes to RV manufacturers.
Should you install an RV furnace filter?
According to the installation manuals I have on both Suburban and Hydroflame, they do not specify an RV furnace filter as of 2022 models. I also checked with Tony Barthel who has the daily review of units and a forum and he also indicated that he has not seen one.
I do think it is a good idea as the typical RV will have dust and pet dander just like a home. Maybe even more so. However, any restriction in airflow will result in the unit overheating and limit out or have limited airflow to raise the sail switch. Maybe a filter similar to the air conditioner unit that is a plastic mesh type that provides little filtering properties, but doesn’t restrict airflow would be a good idea. However, I would not suggest modifying your existing unit with a filter, rather invest in a good portable air purification product?
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.
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Dave, Our 2003 Winnebago Adventurer 35U used a basement AC and furnace. It came with an 1 by 16 by 20 filter. It was accessed by lifting the bed platform. Not sure if it was factory, looked to be designed that way.
That was called True Air and if memory serves me, the filter was only for the cold air return of the compressor? I’ll be working on one next month for video content and will investigate further. In the mean time, Winnebago has great diagrams online in the owner resource center so I’ll look into that this weekend. Thanks
Dave, our 2015 Crusader has a filter on the return. It uses vent filters stapled to a cardboard frame on the back of the metal return vent
I installed a filter in my 2001 Holiday Rambler Endeavor. The return air is located beneath the refrigerator. I simply bought a large enough size regular HVAC residential filter at the store. Cut it to size to fit the door, or closer, cover at the return. Stretched it out and stapled it to the door on the back side and reinstalled the door cover. It works great for my allergy’s. I replace it periodically.
I was thinking of doing something like that to keep the dust out from there. It always gets so dusty in there by the furnace.
If you change your roof top AC filters look at what they catch. Seems like a good idea for the furnance manufacturer’s to make the change. But, will they take one penny out of their profits to make the design changes required to make it work and safe. From a working member of the PHCC industry-Plumbing, Heating, Cooling Contractors Association.
Dave: I have a 1994 Vectra 34 WMCA with that marvelous “TrueAir” A/C. It works perfectly and yes the 16x20x1 filter is under the couch. The Suburban furnace is under the kitchen stove cabinet as is the return air vent in the cabinet kick-plate. I too, have wondered about a filter for the cold air return as the floor is understandably, always dusty; so it must be taking in dust to the furnace as well. My tho’t was a fiberglas filter material like the A/C unit uses. Any ideas on that?