Those are Fahrenheit. The chart is from a Hydroflame service manual- here is the preceding text:
Hydroflame wrote:
A furnace is a consumer's friend when the outside
temperature gets colder. Unfortunately though, cold is an
enemy of LP gas. The BTU capacity of LP per volume
decreases as the outside temperature gets colder. Therefore,
based on how full the LP tanks are, the ambient temperature
outside and how many BTU's the furnace is, there may not be
enough gas to sustain ignition on the furnace.
Using the charts below, let's say that a 40,000 BTU furnace
won't fire up, and we also know that the 65 lb. LP bottle on
the RV is 40% full and it is 0 degrees F. outside. One's first
thought might be that the burner or valve is bad. However, if
we use the chart, the vaporization capacity of the tank in
these conditions is only 38,500 BTU's. The furnace is not
going to perform very well because there is insufficient BTU
capacity in the tank.
If you were to put an insulated fire resistant blanket over the
tanks and a 75 watt light bulb under that, you would probably
raise the temperature of the bottles 10-20 degrees and
almost double the BTU capacity of the tank. This in turn
would allow the furnace to operate properly. So keep in mind
that a furnace problem is not always a component problem.
