On 03/12/2014 20:23, 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? Thanks

IMHO using a paraffin heater is a double-edged sword. Yes, you will get
heat to protect frost-sensitive plants, but the more moisture you put in
the air, the worse the problem of fungal attack. In fact, because air at
low temperature holds less water vapour than warm air, the relative
humidity in a greenhouse at 1°C will be considerably lower than one at
5°C. So if the plants will withstand the lower temperature, the problem
of fungal attack is lessened when compared with the higher temperature.
It will also mean lower heating costs, of course.

I keep my greenhouse at 1°C (provided by a thermostatically-controlled
fan heater). More importantly, I keep the air moving continuously with a
small oscillating fan.

--

Jeff