This is a heat loss for the Foresty Forest’s Chevy Express van.

It shows roughly how much the heat loss would go down if the space between the sheet metal and the inside liner were stuffed with an average of 1.5 inches of wool (eg Havelock Wool) and the floor was insulated with 1 inch rigid Polyiso insulation.

You can download the spreadsheet that this is based on and play with the ForestyHeatLoss

These are rough engineering calcs, so don’t expect them to  be spot on — I’d be happy if they are within plus/minus 20%, but still a pretty good guide.

Bottom line is that if you can get an average of 1.5 inches of wool between the inside liner and the sheet metal everywhere and you added 1 inch of rigid insulation to the floor, you could drop heat loss by more than half.

I did it for an outside temp of -40F, since you have seen this, and its probably about as bad as it will ever get.

All the R values are US R values – to convert these to metric, divide by 5.7.


Foresty Van Heatloss As Is, And With more Insulation
NOTE – R values below are US units – to convet to metric, divide by 5.7.
example: USRvalue 7 converts to MetricRvalue 1.22
All temperatures are F (not C)
This spreadsheet allows you to estimate the heat loss for a camper van conversion.
The uninsulated column below is the Foresty van as it is now (with curtain behind seats and insulating window curtains)
The insulated column shows effect of adding 1.5 inches of wool insulation to walls and ceiling and 1 inch rigid insulation to floor
The non insulated sheet metal is assumed to have sheet metal plus inside liner – Rvalue 1.7
The R value for insulated sheet metal assumes 1.5 inches of wool between sheet metal and inside liner total Rvalue 7.1
See example Rvalue calcs below.
Windows are assumed to be singl glass plus inside curtains – total R vlaue 2.7 (glass and air layers R1, Curtain and air layer R1.7)
Enter the inside and outside temperatures you want used for the heat loss calc.
Change the R values for the insulated version to reflect the insulation you are  using (you can also change areas to reflect your van)
Green squares are values you may want to change to get to your insulation configuration.
The table gives Heat Loss in BTU per hour for both un-insulated and insulated versions, and it gives it for each component (walls, ceiling, windows, …) so you can see where most of the heat loss is.
The plot shows the same heat losses graphically for easiter comparison.
The Totals area gives the total heat loss in BTU per hour and the heating fuel consumption in gallons of propane per hour assuming a 70% efficeint furnace.
Heat loss results are shown in the blue cells.
The spreadsheet is set up for a RAM ProMaster 136 wheelbase, high roof, Windows: back doors and sides.  You can, of course, plug in different areas for walls, floor, ceiling, and windows to match your vehicle
All of the heat losses are and R values are in US units.  To change heat losses from BTU/hr to Watts, divide by 3.412, and to convert US R values to SI, divide by 5.6.
Temperature Inside Van 60 deg F
Temperature Outside Van -40 deg F Note the -40F!!
Back Section: Uninsulated Van Insulated Van
Item Area(sf) Rvalue UA Heat Loss(BTU/hr) Rvalue UA Heat Loss(BTU/hr) % Reduction
Floor 58 1.50 38.67 3867 7.70 7.53 753 81%
Ceiling 58 1.70 34.12 3412 7.10 8.17 817 76%
Walls 63 1.70 37.06 3706 7.10 8.87 887 76%
Wall Windows 34 2.70 12.59 1259 2.70 12.59 1259 0%
Back Doors 18 1.70 10.59 1059 7.10 2.54 254 76%
Back Windows 7 2.70 2.59 259 2.70 2.59 259 0%
Roof Vent 1.4 1.00 1.40 140 1.00 1.40 140 0%
Front curtain/partition 25 2.70 9.26 926 2.70 9.26 926 0%
Air Changes: Volume(cf) ACH Heat Loss(BTU/hr) ACH Heat Loss(BTU/hr) Reduction
Infiltration All 266 2.00 894 2.00 894 0%
Total (BTU/hr) 15521 6189 60%
Total (watts) 4549 1814 60%
> For Chevy Express
Sample USRvalue calcs – note the importance of air layers for uninsulated windows and sheet metal.
> Floor (no insul): Rvalue stackup = Outside air (R0.3) + Steel (0) +  1/2 plywood?(0.5) + Inside Air (R0.7) = R1.7
 Floor (insulated): Rvalue stackup = Outside air (R0.3) + Steel (0) +  1/2 plywood?(0.5) + 1″ polyiso InsulationInside Air (R6) = R7.7
> Windows: Rvalue stackup: Outside air (R0.3) + Window (0) + Inside air (R0.7) = R1.0
>Window + insul curtain: Rvalue stackup: Outside air (R0.3) + Window(0) + middle air (R0.7) + curtain (R1?) + Inside air (R0.7) = R2.7
Gary  Nov 2021



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