Dometic Duo-Therm Non-Ducted A/C Heat Strip Kit, 120V (3314998.000)

If your non-ducted Dometic rooftop air conditioner keeps the rig cool all summer but leaves you reaching for a space heater in spring and fall, this is the part that fixes it. The Duo-Therm 3314998.000 is an electric heat strip kit. It drops into the air conditioner you already own and gives you warm air out of the same ceiling assembly, controlled by the same thermostat. No second appliance, no extra vents, no ductwork.

Non-ducted rooftop units are the simple, popular setup on a lot of trailers, vans, and smaller motorhomes. Cool air comes straight down out of the ceiling assembly instead of running through ducts in the roof. That layout is efficient and easy to service, but from the factory most non-ducted air conditioners only cool. Adding this strip is the clean way to get heat out of the same unit without cutting into your ceiling or finding room for another box.

Here's how it works. The heat strip is a resistance heating element wired with a limit switch. It mounts on the ceiling template under the air distribution box, or ADB, and plugs straight into the control box. Once it's in, the element is part of the system. Call for heat at the wall control and the blower pushes cabin air across the warm element and back out the ceiling louvers. Because it runs on 120 volts, it works on the same shore power or generator circuit that feeds the air conditioner.

Running on 120 volts keeps the wiring straightforward too. There's no separate high-voltage line to pull and no propane plumbing to worry about like you'd have with a furnace. It's electric heat, so it's clean and it's instant.

The limit switch matters. It's a thermal cutoff that opens the circuit if the element ever runs hotter than it should, say from a blocked return or a stalled blower. That's the kind of built-in protection you want in a part that lives in the ceiling and runs unattended while you're asleep or off exploring.

Fitment is specific, so check your model before you order. This strip is built for non-ducted setups. It works with Dometic non-ducted air conditioners including part numbers 457915, 459516, 540315, 540316, 640312, 640315, B57915, and B59516, plus the FJX5357MHE, FJX5457M, and FJX5557M. On the control side it pairs with control boxes 3312020.000, 3313189.049, and 3313189.056, and it seats under air distribution boxes 3314850.000 and 3314851.000. One important limit: it's not compatible with heat pump model air conditioners. Those units already make heat a different way, and the strip isn't the right part for them.

Set your expectations the right way and you'll love it. A heat strip is designed to take the edge off, not to be your only heat source in a hard freeze. It's meant to assist a furnace or heater, not replace one. In temperatures below 40 degrees it may not put out all the heat you want on its own, so if you camp or cruise in genuinely cold weather, keep your furnace in the mix. But for chilly mornings, cool desert nights, and shoulder-season trips, an electric strip that's already tied into your air conditioner is hard to beat. It's quiet, it's simple, and it doesn't burn any propane.

Who's this for? Anyone running a non-ducted Dometic rooftop unit who wants heat without adding a separate appliance. The install is a wiring and mounting job at the ceiling assembly, so if you're comfortable pulling the ADB and making the plug connection you can do it yourself in an afternoon. If you're not, any RV service tech will knock it out quickly. Either way, confirm your air conditioner, control box, and ADB part numbers against the list above first. Get the fitment right and this little strip earns its keep every cool morning you don't have to fire up the furnace.