On 04/12/2014 10:23, Rod Speed wrote:
Brian Gaff wrote

Sounds a bit sus to me, cos a by product of the combustion of paraffin
is water vapour.

Sounds like yet another urban myth to me.

Surely greenhouses are going to be close to 100%
relative humidity at night in weather cold enough
for frost to happen inside the greenhouse.

It is true that condensing and freezing of water vapour helps to hold
the interior temperature steady (as does having a large bulk of water).

I can't see that a very small flame burning paraffin
is going to make any measurable difference at all.

The humble nightlight/candle is good for ~100W I'd guess a paraffin
heater would be ~200-400W minimum. And if you have a too big paraffin
lamp flame it will cover everything in soot. Same if you don't allow
some ventilation and your greenhouse is too well sealed so that it gets
low on oxygen (also very bad for both you and the plants).


john t west wrote

Looking at how some people are protecting their Green Houses against
the frost, i was surprised how tiny the flames were on the paraffin
heaters in the green houses. They were hardly giving off any heat at
all.

I was told its not about the 'Heat', but the fact that the flame
changes the 'relative humidity' in the air'.

Could anyone explain fairly simply, how this actually works?

The heat is also important. Provided that you can replace most of the
overnight losses then it will keep it above freezing. A layer of
bubblewrap on the glass helps keep the heat in a lot better.

I prefer to keep mine about 4C on an electric thermostatic heater. Cacti
do not like the humidity that comes with paraffin.

--
Regards,
Martin Brown