Boondocking Heating

The OFM has been planning and gathering information about remote boondocking for a few months. His usual boondocking for the last 20 years has accidentally been within a hour of a town with supplies etc.  Now we are looking at a new phase of remote not close to supplies and in colder weather above freezing for time frames of a week or so. In the daytime we use direct fired heating like the Mr. Buddy  or others like that. 

 The OFM is a deep south man who likes to sleep no colder than 60 F. Three nights at 25F in Big Bend NP a couple of years ago convinced the OFM a different approach to colder weather boondocking is needed.

 Lots of boondockers sleep with no heat at night relying on blankets etc to stay warm. That works as long as you do not have to make 2-3+ old man trips to the necessity room at night.  The OFM does not like to get up in 45F or lower temps and try to get the Castle warmed up while shiverrrrrrrrring horribly.

The concept of using the onboard furnace in the Castle for comfort heating while sleeping has run into a lot of very “interesting” opinions.  Most of the “experienced” and “knowledgeable” folks that comment on the internet or on videos claim that the furnace will run your batteries down before morning and ruin them. We have run into that statement dozens of times. Never have those folks bothered to tell why the furnace will run your battery down. They never even say how big the furnace is or how much battery capacity they are talking about. But they are the experts. Sure they are!

That is nonsense.  The Castle has two 100AH SLA batteries also known as AGM batteries. They have a listed capacity of 100AH each of which 60% is usable on a regular cycling basis.  We have a serious solar panel system that seldom lets the batteries go below 95% of full.  The Castle has a 25,000 BTU per hour furnace that draws a maximum of 4 amps when running according to the specification label. When we were living in Washington state, the furnace ran about 5 minutes on and 20 minutes off with the temps outside about 25 F. So the heater ran about 20% of the time up there.

Now we go to the 40 F temps we expect for a low but use the same percent of running time .2 or 20%.  4 amps per hour times .2 = .8 amp hour per cycle.
One cycle is 25 minutes.  9 hours of sleep, go to bed and get up time is 540 minutes.

540 minutes/25 minutes= 22 cycles at .8 A/H each.
22cycles times .8 A/H=17.6 A/H used for heating while sleeping COMFORTABLY at 25F outside.

Now let us see 17.6 AH used.  100AH available. Sounds like we could run about 4 nights easily like that without running the batts down for the furnace. Then we can factor in the solar panel input with an average on an over cast day of 12 amps/hour and in 2 hours the batts are back at full charge! On a full mid day sun we get about 18 amps/hour from the panels.

Now what we are trying to figure out is what are we missing that the “experts” know but do not tell.

For those that want to bring up usage during the day, on a cloudy day the panels keep our batts at 12.8 volts or higher. That is what our 9 years of our panel setup has been performing like. That way at bed time we always have at least a 95% full battery set.

If some readers have some constructive comments or information on this electrical usage we would like to hear it. Other things we may not have thought of will be welcome also. We want this new effort to be one of trying to have TOOOOO MUCH FUN. not freezing in the dark.