Heater/Furnace Sizing

java

Expedition Leader
OK guys here goes! I am having a hell of a time sizing a heater for my truck.

I currently have a 40k btu in a 17' floor length truck, its way too much, heater cycles a lot (short cycles). New truck is 12' floor length, but higher ceilings and better insulated. Walls will be R10.5, ceiling is R21. Windows will be double pane (although still not much R value).

From reading online, Airstream uses 20k BTU's in their 20' ish trailers, and 30k in their 31' ish trailers (but not official specs). Earth roamer uses 16k (? varies depending on what page you read on their website).

I am leaning to 30k, because IMO more is better than less (we camp below zero often), but I might get away with 20 or 25? I have an Webasto ST3500, but I think that may be too small at 12k btu's, and I am still going back and fourth on propane vs diesel.



What do you all use?
 

java

Expedition Leader
Ran a heat loss calculator. It says 2886 BTU's needed, but its including 698 from 2 people. Design is for a 15 degree outside temp.

31914566810_b9baf8eaf4_b.jpg
 

pugslyyy

Expedition Vehicle Engineer Guy
OK guys here goes! I am having a hell of a time sizing a heater for my truck.

I currently have a 40k btu in a 17' floor length truck, its way too much, heater cycles a lot (short cycles). New truck is 12' floor length, but higher ceilings and better insulated. Walls will be R10.5, ceiling is R21. Windows will be double pane (although still not much R value).

From reading online, Airstream uses 20k BTU's in their 20' ish trailers, and 30k in their 31' ish trailers (but not official specs). Earth roamer uses 16k (? varies depending on what page you read on their website).

I am leaning to 30k, because IMO more is better than less (we camp below zero often), but I might get away with 20 or 25? I have an Webasto ST3500, but I think that may be too small at 12k btu's, and I am still going back and fourth on propane vs diesel.



What do you all use?

We have a 30k propane in our 18' Bigfoot truck camper.

For the van I am building I am going to try a 2000 Watt diesel parking heater (6800 btu) and potentially add a second one if that is not enough.
 

java

Expedition Leader
We have a 30k propane in our 18' Bigfoot truck camper.

For the van I am building I am going to try a 2000 Watt diesel parking heater (6800 btu) and potentially add a second one if that is not enough.

What size van? I have a 3500 watt diesel one...
 

pugslyyy

Expedition Vehicle Engineer Guy
What size van? I have a 3500 watt diesel one...

E-350 RB work van, no penthouse or windows. We actually sleep in it now without heat and were pretty comfy down to about 13 degrees - just start the motor and run the heater in the morning when we are ready to get up.
 

IdaSHO

IDACAMPER
Insulated well, I you will be just fine with the 12k BTU webasto.


FYI, we can cook ourselves out of our custom camper, in ANY temp, with just a 6k BTU furnace.

We've been to nearly 20 below zero, and still had no trouble maintaining our standard 65 degrees.

Even at that temp, once the cabin was up to temp the furnace only cycled once every hour or so, for just a few minutes at a time.

Ours is an old gravity furnace that I rebuilt and retrofitted with a milivolt valve to run a traditional t-stat.

Super cool setup that uses ZERO electricity. So even if the batteries flatline in the severe cold, we still have heat.

And no blower = basically silent operation.


Only downside to such a small unit is that it takes a bit longer to get up to temp. Still, its only a matter of 10-15 minutes.
 

java

Expedition Leader
Insulated well, I you will be just fine with the 12k BTU webasto.


FYI, we can cook ourselves out of our custom camper, in ANY temp, with just a 6k BTU furnace.

We've been to nearly 20 below zero, and still had no trouble maintaining our standard 65 degrees.

Even at that temp, once the cabin was up to temp the furnace only cycled once every hour or so, for just a few minutes at a time.


Only downside to such a small unit is that it takes a bit longer to get up to temp. Still, its only a matter of 10-15 minutes.

Are you running propane heat? Yeah we generally keep. It about 65, dump it down to 55 at night.

I'm surprised at how little it's asking for. I'll probably temp the webasto in after insulation to see how it does. I don't know if I really want to burn diesel for heat, I only have a 38 gallon tank....



Sent from my SM-G900T using Tapatalk
 

IdaSHO

IDACAMPER
Yep, just a small gravity liquid propane furnace.



The next camper will have a webasto, but this one is about as good as it gets for LP.
 

java

Expedition Leader
Yep, just a small gravity liquid propane furnace.



The next camper will have a webasto, but this one is about as good as it gets for LP.
Thanks! I'm still going back and fourth with webasto vs propane

Sent from my SM-G900T using Tapatalk
 

IdaSHO

IDACAMPER
It certainly should be a hard decision. LP is cheap, as are the appliances.

If you have a diesel vehicle it makes a lot of sense, if you can justify the expense of the appliances.

Ceramic top diesel cook tops, water/cabin heater, etc... are not cheap units.
 

java

Expedition Leader
I have a diesel truck but I want as much driving range as possible... I have a propane water heater, but diesel heater. Hmmmm

Sent from my SM-G900T using Tapatalk
 

java

Expedition Leader
Prepping for insulation, I needed to get some heat in the box. Grabbed a heater from work, its 4800W or 16,378 BTU's, its 32 outside at the moment and hot in the box. No insulation, no windows, door cracked for cords.

So im back to looking at options, diesel heater 11,492 btu's, or propane heater (models come in 16 or 19k)

I dont really want to eat diesel as my tank is pretty small already, 38 gallons, I will likely put a larger one in eventually, but not soon.

Diesel heater will burn .5kg/hr, my math says 1 gallons is 6.4 hours. So lets say we would burn 1-1.5 gallons a day maybe? both draw about 2.8 amps running.

I will have propane for the hot water and cook top, so using that for heat isnt the end of the world....
 

java

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

mezmochill

Is outside
You are doing it the smart way by nailing down general BTUs needed, its easy to overheat in theses small spaces, that leads to cycling/ temp swings.

Propex heater if youve got the tank already, i hear good things. There is the moisture issue. If you ski out of it, you may want a dry heat to dry some of the gear overnight. If its mainly a ski rig, one of those micro wood stoves may be ideal. Just have to keep it stoked. Brings you back to the temp swings. But hey, you end up with a fireplace in your rig. :)
 

java

Expedition Leader
You are doing it the smart way by nailing down general BTUs needed, its easy to overheat in theses small spaces, that leads to cycling/ temp swings.

Propex heater if youve got the tank already, i hear good things. There is the moisture issue. If you ski out of it, you may want a dry heat to dry some of the gear overnight. If its mainly a ski rig, one of those micro wood stoves may be ideal. Just have to keep it stoked. Brings you back to the temp swings. But hey, you end up with a fireplace in your rig. :)

I would love a mini fireplace, but.... I don't have the room. Dry heat is good, the propane units are not bad in that respect (not catalytic ones!) also keeping it stoked, especially the tiny dickson type ones, is a constant process. We leave the dogs in the truck druing the day, and they need a little heat, I doubt they will stoke the fire! :)

Worked in the truck last night. Plastic only on the window holes. a 1500W electric took the chill off (just freezing outside), it was running constantly for ~45 mins.
 

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