Question on Normal Furnace Operation - During Power Failures

**jascott** · 02-20-2021, 02:55 PM

I have a 2015 369RL which we keep on some property in West Texas and use it year round. The trailer is hooked up to a 250 gallon propane tank and I have two Interstate 12v batteries that are a couple of years old. We do not winterize the trailer since we use it year round and the furnace keeps things warm enough when set on 45 to keep everything from freezing.

This week was different and the power company was giving us about 30-45 minutes of power and shutting us off for four hours. This continued for several days while the temps were around 0 degrees. My water heater was left on propane. I assume the 45 min on and 4 hours off was not sufficient to keep the batteries up over the three days of power issues.

Assuming the power went off and the batteries ran down, would I expect the furnace to come back on after a power was restored, or will it stay off since the batteries ran down?

I will not be able to get out there to check things for another week and am just trying to be prepared.

**Bungy** · 02-20-2021, 04:36 PM

Originally Posted by jascott

I have a 2015 369RL which we keep on some property in West Texas and use it year round. The trailer is hooked up to a 250 gallon propane tank and I have two Interstate 12v batteries that are a couple of years old. We do not winterize the trailer since we use it year round and the furnace keeps things warm enough when set on 45 to keep everything from freezing.

This week was different and the power company was giving us about 30-45 minutes of power and shutting us off for four hours. This continued for several days while the temps were around 0 degrees. My water heater was left on propane. I assume the 45 min on and 4 hours off was not sufficient to keep the batteries up over the three days of power issues.

Assuming the power went off and the batteries ran down, would I expect the furnace to come back on after a power was restored, or will it stay off since the batteries ran down?

I will not be able to get out there to check things for another week and am just trying to be prepared.

The furnace will run when the power is on regardless of battery condition, the question is if 30-45 mins on was enough to keep things from freezing.

**D2Reid** · 02-21-2021, 02:09 PM

Originally Posted by jascott

... would I expect the furnace to come back on after a power was restored, or will it stay off since the batteries ran down?

There are several conditions listed here, power on/off, battery run down or not. And how far down did the battery get, below 9.5 volts.

Below 9.5 v the furnace will not come on. When the voltage comes back up it may turn back on unless it has gone into to safety shutdown mode, in which case the only way it will come back on is for someone to turn the thermostat to the off position and then back to the on position.

I am thinking that when the batteries run down below 10v the motor may not have sufficient strength to open the sail switch, this would cause the furnace to go into safe mode and it would not attempt to start again. If the batteries run all the way down to 0 and then the converter comes on providing power to the system the thermostat may be fooled into thinking it was turned off and then turned back on resetting the safe mode. But I think that is kind of a long shot.

Hopefully you have the water turned off while away. I am leaning toward the furnace having failed due to low 12v supply. This in turn would make consider the probability that the water lines froze. Freezing no longer automatically means burst pipes and water leaks, it's still possible, but not as common as it once was.

Please let us know how things work out.

**Bungy** · 02-21-2021, 03:00 PM

Originally Posted by D2Reid

There are several conditions listed here, power on/off, battery run down or not. And how far down did the battery get, below 9.5 volts.

Below 9.5 v the furnace will not come on. When the voltage comes back up it may turn back on unless it has gone into to safety shutdown mode, in which case the only way it will come back on is for someone to turn the thermostat to the off position and then back to the on position.

I am thinking that when the batteries run down below 10v the motor may not have sufficient strength to open the sail switch, this would cause the furnace to go into safe mode and it would not attempt to start again. If the batteries run all the way down to 0 and then the converter comes on providing power to the system the thermostat may be fooled into thinking it was turned off and then turned back on resetting the safe mode. But I think that is kind of a long shot.

Hopefully you have the water turned off while away. I am leaning toward the furnace having failed due to low 12v supply. This in turn would make consider the probability that the water lines froze. Freezing no longer automatically means burst pipes and water leaks, it's still possible, but not as common as it once was.

Please let us know how things work out.

Not true, the furnace will run regardless of battery condition as long as you have ac power. In fact it will run just fine without a battery in the coach at all, I did this for 3yrs when my trailer was at a permanent site- no battery at all.

**pengle** · 02-22-2021, 01:53 AM

Originally Posted by Bungy

Not true, the furnace will run regardless of battery condition as long as you have ac power. In fact it will run just fine without a battery in the coach at all, I did this for 3yrs when my trailer was at a permanent site- no battery at all.

According to the Suburban Furnace Service Manual: "Suburban furnaces operate on 12-volt DC power which is supplied either by a 12-volt battery or a converter system. A recreational vehicle furnace that is specifically designed for “park model” trailers operates on 120 volts AC."

So, you can run the furnace without a battery, if you are plugged into shore power AND you have a converter that is creating 12VDC for the furnace.

The manual also says that the furnace will operate with a minimum battery voltage of 10.5 VDC, BUT it also says that the control board checks for a minimum of 9.5VDC. If the voltage falls below 9.5 the furnace acts like it has NO voltage and completely turns off, but as soon as 9.5 volts is detected (shore power is turned back on) then the furnace will act like you just called for heat by turning the thermostat up.

All of this to answer @jascott that the furnace will come back on when the power comes back on (even if the batteries are below 9.5VDC) and the batteries will start recharging for that 45 min. When the power shuts off again the furnace will continue to run on battery until the battery voltage drops below 10.5 or 9.5 (which is is Suburban?).

There are SO many variables as to whether your furnace could actually maintain your 45 degrees setting (skirted?, wind blowing?, sun out? slides in or out?).

**jascott** · 02-22-2021, 06:06 AM

Thanks everyone for the replies. I'm hopeful that between the ceramic heater, intermittent power, and dual batteries the trailer will not have sustained significant damage. It will be a week or so before I can get out there and check things, but I will report back once I have and update.

**jascott** · 03-15-2021, 06:10 AM

Wanted to post an update....

I spent last week out on the land and I had zero issues with the trailer. I don't know if the furnace ever ran out of battery power and shut off or not, but I did not have any freeze damage to the trailer. On a side note, my father in law has an Imagine travel trailer out there as well and his furnace shut down at some point. He did have several fittings, shower head, etc. freeze and break.

Thanks again for the input!