Heating......again

[claypot]

Looking back through the forum this topic keeps cropping up at around this time of year, and yet again my problems have started.
To-date I have relied on electric heaters in both my greenhouses with propane backup for the intermediate greenhouse and paraffin for the cool greenhouse. Paraffin is not economic these days and is not automatic (it just burns without thermostatic control) and requires constant attention to top up.
My problem is that my latest home is very rural, served by overhead electricity which is unreliable. We have no gas and home heating is oil. Quite apart from alarms etc to know when heat fails to put on backup (if I am around) the supply breaks and surges severely and I believe is damaging my equipment. We cannot, for instance, have digital timeclocks on heating - they just go berserk. Electric heaters have served me well in the past but even they are failing now - either fans or elements.
As I have propane installed for one greenhouse as backup, I am considering switching to propane as my base heating system for both greenhouses because that works reliably without any electricity and keeps very stable temperatures. Automatic changeover of tanks runs smoothly and I have a replenishment source nearby.
Propane runs a Shilton unvented heater with appropriate ventilation for clean burning. Admittedly propane is costly compared with electricity, but I have to consider it against loss of my collections through heater failure. Reliability is the key factor here.
I have never used my unvented propane for long periods so wonder whether there is anyone out there who has such experience. I have never observed detrimental effects on my plants with either unvented Paraffin or Propane.

[Ray]

All gas burners will get "out of tune" over time - i.e., the air-to-fuel ration will shift as the burner becomes sooty or oxidized. As that happens, more and more ethylene is created, which can be toxic to plants.

I had an unvented propane heater that converted a "3-season" room to year-round use, and while it was fine the first winter, after a second, the entire room and its contents were covered in a think layer of soot. It wasn't noticeable until you washed a white surface, then "WOW! Because of that, I would not use an unvented heater again, in the home or the greenhouse.

That said, if it is quality heater and is cleaned and adjusted periodically, it's probably OK. I suppose part of the equation is how leaky the greenhouse is...

[claypot]

Specific dedicated adequate air provision is provided at all times for both the burner and "exhaust" and the burner of the heater is sent for servicing annually - whether it has been used as backup or not. Even then, they make minor adjustments during cleaning. The most I have used this system as backup is 4 weeks with absolutely no impact on my plants.
At least the burner is thermostatically controlled so the main flame decreases gradually as temperature is met then increases again for boosts as necessary. I would certainly not consider anything other than a premium brand of heater.

[fishmom]

It also depends on whether or not expanding your reliance on fossil fuel is an issue for you.

[claypot]

absolutely not. Be it oil, electricity or gas they are all fossil for us.

[richardb]

I also have propane available for backup using an unvented heater but have paid particular attention to fresh air at the burner and never had any problems with plants. I have no experience of long term use though.