You might be thinking that its not worthwhile insulating the floor on your camper van conversion. I think this would be a mistake.
This question came up on the ProMaster Forum the other day, with some opinions on both sides. I did a little test on my van to try and see how worthwhile it is to insulate the floor and posted it on the Forum — its pasted in below.
It seems like the bottom line is that if you have a van that is well insulated, and you don’t insulate the floor, the heat loss for the whole van will be about 40% more than the same van with an insulated floor!
Test to Determine Value of Floor Insulation in Camper Vans
Here is the Post:
I took some temperature measurements in my PM conversion yesterday to try and get a better idea how much difference floor insulation makes.
My van is a 2014 136 WB highroof that has been converted to camper van – details here: http://www.buildagreenrv.com/our-conversion/
The van insulation is basically 1 inch of spray polyurethane in walls and ceiling, and 1 inch of rigid polyiso foam board in the floor — we also use Reflectex plugs in the windows at night. Our van has a center aisle that runs full length, with bunks aft on either side – so there is exposed floor from front to back.
To get the temperatures settled down in the van, I ran the furnace for a couple hours before measuring temperatures. The outside temp was 34F.
The furnace in my van is an Atwood 12K BTU input (9K BTU output) propane furnace. It just blows hot air (135F) out into the space near the galley at about 1 ft off the floor. It cycles off and on to maintain the temperature you set.
I measured temperatures at these locations:
Ceiling air (1 inch below ceiling level near center of van)
Bunk level (about 20 inches off floor)
Floor at several points (2 inches above floor level)
Floor right near the back door, where there is no insulation.
A spot high on the back door that has no insulation
Took a lot of measurements, but concentrated them down to this one set, which I think is representative:
Bunk Level 61F
Floor – distance from back doors:
Floor 1.5 ft fwd of back door 50F
Floor 3 ft fwd of back door 52F
Floor 4.5 ft fwd of back door 54F
Floor 6 ft fwd of back door 56F
Floor 7 ft fwd of back door 76F (near furnace)
Floor 9 ft fwd of back door 61 F (near cab step)
Uninsulated floor temp near back door 38 F
Uninsulated spot high on back door 45 F
Outside temperature 34 F
Note that the floor temps are air temps measured about 2 inches off the floor – the floor surface temps run about 2F cooler as measured with an IR temp gun.
Ceiling temperature averages 66F, and does not vary a whole lot over the length of the van.
The floor temp varies quite a bit from front to back mostly due to how much of it the furnace outlet sweeps it in a given location. Its coldest near the back of the van at 50F and warmest opposite the furnace at 76F (10F warmer than ceiling).
The average floor temperature is 58F.
The difference between the ceiling temp and the average floor temp is 8F – that is, on average the floor is 8F cooler than the ceiling. Not so bad really, but this is in part because the furnace blower keeps things somewhat mixed up. It sounds like RD gets the same sort of mixing from his Espar furnace. As KIP pointed out, a heater that does not provide mixing would result in much more difference between ceiling and floor temperatures.
I think that if you use a heater that does not keep the air mixed up, it would probably be worthwhile to have some kind of DC fan to keep the air mixed up.
The bunk level runs about 5F cooler than the ceiling.
One message to me is that it would make for a warmer floor over the whole van if I had a simple duct system on the furnace that would have a forward and an aft outlet that would blow the furnace air over more of the floor. Hard for me to do this now, but something to think about for new conversions.
The uninsulated floor is 20F colder than the average of the insulated floor.
Heat Loss Equation:
The heat loss of a wall or floor or ceiling is calculated as:
Heat Loss = (Area) (Tinside – Toutside) / Rvalue
Area is the area of the wall or floor – about 70 sqft for the PM ceiling or floor.
Tinside – Toutside is the temperature difference between the inside and outside.
Rvalue is the thermal resistance of the material to heat flow (eg polyiso R6 per inch, wood R1 per inch,…)
This is pretty much the universal heat gain or loss equation – its used all over the HVAC industry, and makes common sense – loss goes up as the area gets bigger, and as it gets colder outside, and heat loss goes down with for materials with more resistance to heat flow (insulators). It also works in the summer to estimate heat gain. Note that the equation does not care if the heat is flowing up, down or sideways.
Heat Losses Based on the Measured Temperatures:
Heat Loss my insulated Ceiling = (70 sqft) (66F – 34F) / R8.1 = 277 BTU/hr
Heat Loss my insulated Floor = (70 sqft)(58F – 34F) / R7.6 = 221 BTH/hr
So, the ceiling loses about 25% more heat than the floor – mostly due to the temperature stratification.
If the floor had no insulation, the heat loss would be about:
Heat Loss bare metal floor = (70 sqft) (58F – 34F) / R1 = 1680 BTU/hr (8X the insulated floor)
If the floor had just half inch plywood (R0.5), the heat loss would be about:
Heat Loss plywood Floor = (70 sqft)(58F – 34F) / R1.5 = 1120 BTH/hr
So, big reduction in heat loss with insulation.
If you go through the heat loss for my whole van with the above temps, it comes out 1964 BTU/hr for a floor insulated to R7.5 vs 2754 BTU/hr for a floor with just half inch plywood – a 40% increase in total van heat loss for not insulating the floor.
Pro/Con on Floor Insulation:
Its cheap and easy to do ($40 materials and an hour of labor)
Not insulating the floor (plywood only) increases total heat loss for an otherwise well insulated van by about 40%.
Allows a smaller furnace to be used, or the same furnace to be good down to colder outside temperatures.
Less heating fuel used – cost saving, carbon emissions saving, and fewer tank refills.
If you used a separate fuel for heating, it allows a smaller tank to be used and last longer (allows me to use a standard BBQ propane tank).
It makes the van more comfortable by making the floor run warmer and decreasing the difference between floor and ceiling temps – especially if you have a furnace that keeps the air mixed.
It also helps in the summer to reduce heat gain. It should be even more effective in that the temperature stratification that makes floor insulation a little less effective than ceiling insulation for heating makes floor insulation a bit more effective than ceiling insulation for cooling.
You lose a little headroom (unless you use the uNik method or the RD method)
I realize some people are tough as nails (used to be that way myself 😊), and this warm floor stuff is just for wimps, but I’ve gotten soft enough that warm floors are kind of nice. Through some stroke of luck, the warmest spot on our floor is right in front of the composting toilet – makes a big difference for that barefoot toilet run at 3 am 😊