Most travel trailer furnaces are propane, but you need 12 volts for the ignition, circuit board, and the big pull is the fan. Furnaces are hard on battery charges because of the fan.
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Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
In the oldies trailers you had a gravity furnace that needed no power. But now most of the furnaces run on 12 volt and will drain your batteries quite fast.
For dry camping in all but the warmest climates or for more than two days at a time you will want lots of battery capacity. Most travel trailer (pull trailers) have room on the tongue for two batteries. Some will need to be modified to make room for two but it can be done.
on the Roo, your furnace fan runs on 12v and ignites on 12v.
the heat comes from propane. even when plugged into shore power, the converter converts 110v to 12v to run and ignite the furnace.
no electric heaters in the Roo. there is room for two batteries on the tongue. we dry camp almost all the time and i got two batteries for my Roo. you can have RVW add a second battery which i recommend doing, since you should have matched batteries.