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Old 10-19-2016, 12:18 PM   #1
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Unhappy Suburban furnace expectations

I have a Rockwood 2304S with a Suburban NT-16SQ furnace and 2 Interstate Deep Cycle Extreme 6 volt batteries. They are rated at 122 min @ 75 amps (232 ah). The salesman said I could get four days of dry camping if I was careful. Everything works just fine except the heater. I am lucky to get two days and nights of limited use on my furnace. I usually only use it to warm up the rig in the morning for 30 - 40 minutes. It is the most unreliable on colder nights. I have taken my rig to the dealer three times over the last two years. First time they said my propane wasn't properly bled. The second time they said they found a gas line kink. The third time they said I am expecting too much from my furnace and that it works just fine. After a ruined trip I made a test in my driveway. I slowly ran my battery down until the furnace stopped working. I then turned on all the light, started the water pump, ran the slide in while operating the electric jacks. Everything worked normally. Am I expecting too much from my furnace?
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Old 10-19-2016, 12:24 PM   #2
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No. You're expecting too much from your batteries.

How do you know when the salesman is lying to you? - His lips are moving!
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Old 10-19-2016, 03:29 PM   #3
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I find it very interesting your heater drops out for low voltage before anything else. I would invest in a digital voltmeter/ammeter and re-run your test with everything off but the heater, measuring battery voltages at the start (full charge is 12.7 -12.8 volts). Are the batteries full when you start the test? I would also check how many amps your heater is drawing, and compare it against placard and manufacturer specs. After the heater cuts off for low voltage, leave everything off for an hour and re-check battery voltage.

How old are the batteries? How many times have they been deep-cycled? There is a good chance the batteries won't hold much of a charge any more, just like an auto battery that's been run low too many times. You may not have anywhere near the rated 116AH available.

We sized our batteries to run the heater in our A-frame for 4 nights of dry camping. But the A-frame heater fan only draws 4 amps, and the thermostat next to nothing. We figured 20 amp-hrs per night to run the heater for 5 hours on 4 nights in the 30s or high 20s. The A-frame has a very small volume to heat, and the fiberglass/foam roof and upper sides have some insulation. Add another 4-5AH per night for propane/CO detector, minimal use of LED lights, and the thermostat.

You will have to do a similar calculation and evaluation to stay within 116AH for 4 nights (29AH per night). It is possible, but not likely, for a TT to stay under 29AH per night while using the heater. That's what the salesman meant by "careful".

Fred W
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Old 10-19-2016, 04:20 PM   #4
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As pgandw says, the batteries may not be getting a full charge to start with. Leave your trailer plugged into shore power for 72 hours without running the furnace. Then unplug from shore power for 4 hours and check the battery voltage, should read between 12.7-12.8
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Old 10-20-2016, 05:07 AM   #5
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Quote:
Am I expecting too much from my furnace?
Yes, and also expecting to much from the batteries.


Your other items, water pump, jacks, slides will probably continue to run even when your batteries are dropping down below 9 - 10 volts.

However, the combustion blower in your furnace isn't turning fast enough to safely support combustion, so the furnace doesn't light.

Your furnace has a safety device called a "Sail Switch". Basically, its job is to measure the air pressure (air flow) in the combustion chamber to ensure the combustion blower is running.

Anything that prevents adequate air pressure or restricts combustion air flow will prevent the propane from being turned on. A Low battery is the most common as the blower isn't turning fast enough to activate the sail switch. ALSO, blocked combustion air vents can prevent adequate air flow, even on a fully charged battery. Look outside where your furnace exhausts, make sure bugs didn't set up housekeeping in the intake or the exhaust vents.
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