As odd as it is, sometimes an RV manufacturer will neglect to install a furnace vent where you need it most, like in the bathroom or bunk house. It’s no fun making that 2-in-the-morning trip to a freezing bathroom. This mod is about adding that missing furnace vent using one of your unused furnace air distribution box outlets.
The furnace air distribution box, as its name implies, distributes the heated air pushed in to the box by the heater fan. Metalized hose is attached to a duct collar which is attached to the box, and this hose runs to the heater registers in your RV. In most RVs with this type of furnace, there are always a few outlets that are unused and blocked off with a removable duct plate.
So we start by removing the furnace grill and taking a look around the air distribution box for an unused outlet. For those furnaces that force the air out the bottom of the box to floor-mounted registers, it may be a tight fit between the box and the compartment. In this case, patience is a virtue as removing the blocking plate and adding the duct collar can be a bit trying, but it can be done!
At this point, you should make sure you have a duct collar, 4″ dryer duct hose long enough to run to where you want the new heater vent, a few 4″ clamps, a heater register, and a 4″ hole saw, all of which can be purchased at your local RV parts store and/or local home improvement store.
After you find an unused outlet, remove the duct plate and replace it with the duct collar. This collar twists in to the outlet and can also be secured using a single sheet metal screw if you have the room to get a screwdriver in there. Now look around the compartment and see how you will route the dryer hose to the heater register. If you’re lucky and you have some cabinetry running the length from the furnace to where you want the register, you can just route the hose through the back part of the cabinets. If not, you will have to get creative.
Attach the hose to the duct collar using a 4″ clamp. Make sure you slide the hose all the way on to the duct collar. Otherwise, as you tighten the clamp, you will just crush the hose. Route the hose through the cabinetry to where you will mount the new register. Now using the hole saw, carefully cut the register hole taking care that there is nothing behind the hole, like wiring or plumbing. Reach in and carefully slide the hose through the hole. Attach the hose to the register using another clamp. Slide the register in to the hole, secure with screws, and now you have heat right where you need it!
If the length of the hose to the new register is longer than 15 ft. or there are many bends in the hose to accommodate routing, you can add a small muffin fan at the register to assist flow. Simply wire the fan’s power to the heater’s thermostat so it will automatically turn on and off with the heater’s fan motor.