On 04/12/2014 21:13, David wrote:

snip


What a load of codswallop.

yes

This is the most ridiculous topic we have had for a long time.

yes

If humidity would keep out the frost then a misting unit using warm
water would do the job without the risk of pollution by a badly set flame.
Blue flames on a paraffin heater give virtually no pollution,

except for 1.4 times as much water vapour as the paraffin they consume

it's a
yellow flame that gives you carbon that can coat everything and will
also have a sulfur element

No, you will get exactly the same amount of sulphur dioxide from the
blue flame
..
In the dim and distant past you would use a paraffin sump heater
(designed to fit under the car sump to stop it getting to cold in severe
frosts) as frost protection in a very small greenhouse, also cover
plants at night with sheets of newspaper to keep the frost off.
Then there was low voltage soil warming using Galvanized fencing wire,
the idea being that if you kept the soil to around 50f then the air temp
around the plants would keep frost off with minimal heating.