Rear (Propane) Heater Question

[DCMac]

How long should it take for my rear heat-air unit to start blowing warm air? Heat is propane only.

Got overly chilly the last few days camping on the Gulf, DW wanted both heaters on. Ran the unit maybe two minutes and it was blowing ambient temperature. Tried again next night, same. Third night just for giggles decided to let it run longer and after what seemed like five minutes it started blowing warm. Surprises me because the 5er we had before blew warm almost immediately.

[Jim_HiTek]

Heat pumps will behave that way depending on ambient temps and I believe humidity. At least it seems that way. A long time for it to blow warm is usually dependent on the outside air temp. It also helps if your condenser fins are clean of debris like leaf matter.

If you have a thermometer, you'll see that the air from the vents does slowly increase in temp.

Wait...propane! Doh. It shouldn't take hardly any time at all. It's suppose to light within 3 tries. If it doesn't light, the furnace fan will keep running for 2 minutes than shut down and you have to toggle the Off/On switch for it to try again. Do you have plenty of gas? Is there anything blocking the air intake outside the RV? A chair perhaps?

[creativepart]

The Propane furnace works like a gas oven or water heater. It starts and gas begins flowing, the igniter attempts to light a pilot and once that lights there is a thermistor that sense the presence of the flame and once this is confirmed the gas to the main burner is released and whosh the warm air starts.

The furnace has a routine built in that it will keep trying to light the pilot and failing after a number of attempts and checking for temp at the thermistor. If it doesn't find the flame/heat it's expecting after a couple of minutes it will turn off the heater.

All the while it's doing this it will be blowing cold air through your registers.

Anything more than a minute does seem pretty lengthy. Of course, if the propane hasn't been used at the stove, RV Fridge or the water heater before the furnace's gas regulator opens it could be a while until the low pressure propane gas gets back to your furnace.

And, if it's below freezing outside it can take propane longer to boil off and supply a steady flow of gas to the heater.

As Jim has pointed out, it can also be a sign of a malfunction in the furnace.

I've never timed my furnace, but I would guess that mine ignites between 1 - 2 mins at maximum.

[Jim_HiTek]

RV gas furnaces have one other safety device built in, a 'Sail Switch'. This device is to sense air flow from outside into the combustion chamber. If the sail switch goes bad, and that's the typical item that fails on them, it won't toggle the gas valve ON so no heat. If it does fail, than the furnace may not need to be removed, as the switch can normally be tested with just the cover off, but the cover does need to be removed.

Note that there is no air connection between the outside air and inside air. There's a heat exchanger that does the job of heating the inside air after the inside fan draws in house air.

[eaglelen]

I have a 2019 Adventurer 35F and only have 1 propane heater in the front (and 1 front heat pump). The rear system is just a heat pump. It takes several minutes to get "warm", and comes out the roof vent. The front thermostat has both "heat gas" and "heat elec" modes, whereas the rear thermostat only has "Heat". The ductwork from the "front" propane heater extends to the rear of the coach, and is in the floor.

[NeilV]

The battery also needs to be charged up enough to run the combustion fan fast enough to satisfy the sail switch so when dry camping the condition of the battery is also a consideration. The propane furnace like the generator does need to be exercised every now and then to keep the propane line purged, bearings on the blowers spinning freely and the combustion chamber free of cobwebs/mud dauber nests so there are many reasons why the heat may not kick right away or on the first try especially when the furnace is seldom used.

Sometimes it may have to be cycled on and off several times to free everything up and the outside vents may need to be blown out with a shop vac or electric leaf blower being careful to only apply a blower to the inlet and not the outlet so you do not chance forcing the sail switch backwards and damage it. Stand back, wear a dust mask and eye protection when you blow it out as there can be a bit of debris or even a few residents that may get blow out the exhaust outlet when you do this bit of maintenance which is too often overlooked until after a problem has been experienced.

[macnut]

Originally Posted by creativepart

The Propane furnace works like a gas oven or water heater. It starts and gas begins flowing, the igniter attempts to light a pilot and once that lights there is a thermistor that sense the presence of the flame and once this is confirmed the gas to the main burner is released and whosh the warm air starts.

The furnace has a routine built in that it will keep trying to light the pilot and failing after a number of attempts and checking for temp at the thermistor. If it doesn't find the flame/heat it's expecting after a couple of minutes it will turn off the heater.

All the while it's doing this it will be blowing cold air through your registers.

Anything more than a minute does seem pretty lengthy. Of course, if the propane hasn't been used at the stove, RV Fridge or the water heater before the furnace's gas regulator opens it could be a while until the low pressure propane gas gets back to your furnace.

And, if it's below freezing outside it can take propane longer to boil off and supply a steady flow of gas to the heater.

As Jim has pointed out, it can also be a sign of a malfunction in the furnace.

I've never timed my furnace, but I would guess that mine ignites between 1 - 2 mins at maximum.

I have a similar issue. All other gas appliances are working fine, but the suburban furnace is not working. The fan kicks on like normal but the gas does not ignite. After about a minute, as CreativePart mentions above, the furnace turns off. The manual provided by Winnebago does not provide troubleshooting advice, and says to have a trained professional do any repairs. I’ve already scheduled an appointment when I return from the trip, but thought I’d reach out to the group in case there are any simple things I can try.

[Jim_HiTek]

Originally Posted by macnut

I have a similar issue. All other gas appliances are working fine, but the suburban furnace is not working. The fan kicks on like normal but the gas does not ignite. After about a minute, as CreativePart mentions above, the furnace turns off. The manual provided by Winnebago does not provide troubleshooting advice, and says to have a trained professional do any repairs. I’ve already scheduled an appointment when I return from the trip, but thought I’d reach out to the group in case there are any simple things I can try.

With my Suburban, the only way I could tell anything was to remove the chrome external parts, then pry off the cover plate after removing numerous screws, some covered with black butyl. That caulking was on there thick and I bent the cover a bit prying it off. So be careful.

Now that you're in there, you can check the sail switch as it's generally positioned where you can see it, measure it or replace it, without removing the furnace. Check all the electrical connections and connectors you can to make sure there's no wires pulled out or poor connections. Then I used a DVM to measure the wires from the thermostat to make sure it was working.

Have someone switch it on at the thermostat and then listen. Fan should start. You should smell propane and then 15 seconds later hear 'sparking', a pause, more sparking, another pause, more sparking. If it hasn't made any sparking or whooshing sounds by now, it's going to shut down and the fan will keep running for 2 minutes. If you try this 3 times, the circuit will shut it off for several minutes, 15 I think, so you can't even test it.

If that's what happens, you can dig deeper with your own testing and shut off the propane, disconnect from the furnace, plug the open end of the propane supply pipe, remove the two screws holding the furnace, pull it out and check it out on a picnic table. Then inspect everything, clean the terminals, resistance measure the motors and the propane valve, OR, pull it out a few inches, and call a mobile tech. They'll have an extension hose, and a stand tall enough to put the furnace on right next to the RV for testing. Usually.

[macnut]

Thanks Jim HiTek. Much of that is beyond my capabilities, except maybe the “call a mobile tech” part, but I’ll do what I can! :-)