Heater/Furnace Sizing

[dwh]

Personally, if you've already got the diesel unit, I'd use that. 3 gallons a day, maybe less. Probably less. So, add another tank if need be. It'd help range as well.

Doing nothing but cooking 3 squares a day, I get 10 weeks out of a 5 gallon tank of propane. Using it for heat, running the fridge and hot water can suck down 5g in a couple three days.

 

[java]

Personally, if you've already got the diesel unit, I'd use that. 3 gallons a day, maybe less. Probably less. So, add another tank if need be. It'd help range as well.

Doing nothing but cooking 3 squares a day, I get 10 weeks out of a 5 gallon tank of propane. Using it for heat, running the fridge and hot water can suck down 5g in a couple three days.

Yeah a titan tank is on the long term wish list. 3 gallons is 30 miles of driving.... I get 5-7 days out of 6 gallons (not all the way empty but close) heating and cooking. Fridge is 100% electric.

I dont believe there is an extra pickup in the stock tank, so I would have to drop the tank to add one.

 

[fluffyprinceton]

I dont believe there is an extra pickup in the stock tank, so I would have to drop the tank to add one.

Maybe not if the top of the tank is accessible - with a Espar it's just a small bolt with a tube running through it - so just drill & tap for the bolt.Moe

 

[java]

Maybe not if the top of the tank is accessible - with a Espar it's just a small bolt with a tube running through it - so just drill & tap for the bolt.Moe

Ill find out soon! Wife told me just top use the Webasto. Had a 1500W (~5000BTU's) electric in there last night while I was working and it was warming it well enough for no windows.

 

[Mwilliamshs]

OK bumping this again, Looked at the Truma heaters.... Mini propane powered, 3800W, three outputs, lots of fan options, and claims ~98% efficient.

The complexity of those units is a turn off for me. Not to mention $$$ and limited availability/support in the US. I know there are people who use them happily but they're typically in the Camping World club and unlikely to venture off the beaten path or be in harm's way should their furnace fail. I know the more traditional furnaces, like the Atwood Everest Star for example, are less efficient (~70% fuel and ~2 or 4 amps DC) but are also more reliable and through MacGuyver-ing, I can make mine work no-matter-what, unless of course the heat exchanger itself fails.

Not exactly expedition-style but we use a 30' 5th wheel travel trailer for deer hunting in Kansas every winter. It's a boondocking situation, fully self-contained, no outside connections. The propane furnace that came in the camper is an Atwood 8535, 34k BTU. It's too big. It runs just a few minutes at a time then shuts off and fires up again a few minutes later, etc. Textbook "short cycling" and because these furnaces run cool till the sail switch closes, then burn till satisfied, then run cool again till the exchanger cools, there's a good deal of air movement that is not actually making heat (JUST LIKE WEBASTO, ESPAR, PROPEX, ETC). It doesn't go through too much fuel (we take 160 lbs for the week and always have plenty) but it eats up DC quickly. The plan is to go to a 8520, 20k btu. There's also a 16k btu model but I'm hesitant to cut our heat by THAT much. This change will take our power consumption for heat from 9.8 amps to 4.6 amps. HUGE difference IMO. These furnaces all use the exact same cutouts, housing, access door, etc etc etc. I mention all this to say that just because a furnace looks like one with which you're familiar, it can be totally different. "I had one just like that and it killed my battery in a day" is what a guy told me and I believed him, but then I learned two otherwise identical furnaces could have DC draws that differ by over 50%. A local RV scrapper guy from Craigslist has agreed to trade furnaces with me, my 34k for his 20k, even up so I'm tickled. I'll use a cheap programmable thermostat (runs on AA batteries) at the time of the swap to save even more energy and gain a more easily adjusted run-time.

 

[java]

The complexity of those units is a turn off for me. Not to mention $$$ and limited availability/support in the US. I know there are people who use them happily but they're typically in the Camping World club and unlikely to venture off the beaten path or be in harm's way should their furnace fail. I know the more traditional furnaces, like the Atwood Everest Star for example, are less efficient (~70% fuel and ~2 or 4 amps DC) but are also more reliable and through MacGuyver-ing, I can make mine work no-matter-what, unless of course the heat exchanger itself fails.

Not exactly expedition-style but we use a 30' 5th wheel travel trailer for deer hunting in Kansas every winter. It's a boondocking situation, fully self-contained, no outside connections. The propane furnace that came in the camper is an Atwood 8535, 34k BTU. It's too big. It runs just a few minutes at a time then shuts off and fires up again a few minutes later, etc. Textbook "short cycling" and because these furnaces run cool till the sail switch closes, then burn till satisfied, then run cool again till the exchanger cools, there's a good deal of air movement that is not actually making heat (JUST LIKE WEBASTO, ESPAR, PROPEX, ETC). It doesn't go through too much fuel (we take 160 lbs for the week and always have plenty) but it eats up DC quickly. The plan is to go to a 8520, 20k btu. There's also a 16k btu model but I'm hesitant to cut our heat by THAT much. This change will take our power consumption for heat from 9.8 amps to 4.6 amps. HUGE difference IMO. These furnaces all use the exact same cutouts, housing, access door, etc etc etc. I mention all this to say that just because a furnace looks like one with which you're familiar, it can be totally different. "I had one just like that and it killed my battery in a day" is what a guy told me and I believed him, but then I learned two otherwise identical furnaces could have DC draws that differ by over 50%. A local RV scrapper guy from Craigslist has agreed to trade furnaces with me, my 34k for his 20k, even up so I'm tickled. I'll use a cheap programmable thermostat (runs on AA batteries) at the time of the swap to save even more energy and gain a more easily adjusted run-time.

The Truma I was looking at is heat only. Much less than their Combi units. BUT not available in the US yet....

I have the same issues with my current RV furnace, its a 40k in a 17' truck.... Short cycles like crazy.

I think I am sold on the Webasto 3500, but my second choice would be a Suburban 16k (or propex but $$), just for packaging size. Much smaller than the Atwood's

 

[Mwilliamshs]

The Truma I was looking at is heat only. Much less than their Combi units. BUT not available in the US yet....

I have the same issues with my current RV furnace, its a 40k in a 17' truck.... Short cycles like crazy.

I think I am sold on the Webasto 3500, but my second choice would be a Suburban 16k (or propex but $$), just for packaging size. Much smaller than the Atwood's

The Suburban 16k and Everest Star are very close to the same size, Atwood smaller in 2 of 3 directions. I like that the Atwood has a lot more metal in it and I've never had a Suburban appliance that held up long term. Water heater leaked (tank weld), furnace heat exchanger cracked. But the everest star in my Lance cabover is great. Atwood water heater I swapped in place of the suburban is tops. 10 gal, dsi, propane and electric. YMMV

Suburban 16 dimensions: 9-3/8" H x 9-3/8"W x 21-27 3/8"

Everest StarDimensions: 20.5" (L) x 8.375" (W) x 11.375" (H)

 

[shirk]

Bumping an older thread while researching BTU / W heat requirements.

Java do you think the heat loss calculator is accurate? The Webasto 3500 is still roughly twice the BTU's output compared to the calculated requirements.

IdaSHO's comment on being able to cook themselves out with 6k btu leads me to think the ~3k btu requirement is correct.

 

[IdaSHO]

For the record, our 6Kbtu is still more than enough

 

[shirk]

For the record, our 6Kbtu is still more than enough

I guess the question is, how much more than enough? Do you think you have 2x more heating capacity than needed?

Is your fresh air exchange open roof vents/windows?

 

[IdaSHO]

Not 2x I believe it to be sized appropriately, as it doesnt short cycle, and has zero problem keeping the cabin at 68 degrees (typical t-stat setting) in weather below zero degrees F.

ventilation is important in any serious cold weather situations.
We have a permanent roof vent that mitigates any kind of condensation issues, almost regardless of weather and temps.
When we need more air exchange, a window (or two) is cracked a bit. Still, the heater doesn't have any trouble maintaining temps.

It truly is a set it and forget it, simple setup. Something I really do appreciate.

 

[Joe917]

Our box is 18'X8'X7', 2 1/2" composite walls, 4" composite floor, 3" composite roof.
Heat is a Webasto ThermotopC. Cabin heat from 2 cabin large radiators and one crawl space radiator.
Last year in -20C I kept the cabin at 20C using 4 liters every 24 hrs
at 0C to -5C that fuel consumption dropped to about a liter every 24 hrs
I was burning furnace oil from an external fuel can so I was able to monitor fuel use.
We also have a 450 liter diesel tank.
Hopefully those consumption numbers help.

 

[java]

Bumping an older thread while researching BTU / W heat requirements.

Java do you think the heat loss calculator is accurate? The Webasto 3500 is still roughly twice the BTU's output compared to the calculated requirements.

IdaSHO's comment on being able to cook themselves out with 6k btu leads me to think the ~3k btu requirement is correct.

My 3500 is still too large IMO. It over shoots the temp setpoint during the cool down cycle.

I always leave a maxxfan on low in winter to keep moisture down.

Sent from my SM-G973U using Tapatalk

 

[shirk]

Thanks for the information.

As the camper structure's have become better insulated and sealed it only makes sense that they require less heat and better circulation. Just wanting to confirm real world use vs theory.

It would be good so see some more modern hvac techniques applied to lower the energy consumption needed to heat these tiny little spaces.