Don't waste heat.

[DaveW]

Perhaps not the opportune time to raise the subject in the USA with your falling oil and heating costs, but energy costs will inevitably rise again in future and anyway the money you save on heating this winter is available to buy more plants or even build a bigger greenhouse. In Europe however many forms of greenhouse heating costs continue to rise.

Unless you are growing the more tropical cacti including some epiphytic ones most do not need excessive heat in winter, in fact it can be a disadvantage. This quote is from a UK collector in the BCSS Journal on his greenhouse:-

"It is heated by four electrical tube heaters, 1kw each and measuring 6ft (1.8m) long. The thermostat was set at 11C (52F) for a couple of winters, but I found that paradoxically, I got more flowers following a winter when temperatures were set lower at just 6C or 7C (43F or 44F), confirming that cacti reward you more when challenged during their resting period."

A quote from the following link on greenhouses:-

"Reducing the night-time temperature by 5 degrees F can reduce the heating bill by 10 to 20 per cent in northern climates."

https://books.google.co.uk/books?id=OsM ... re&f=false" onclick="window.open(this.href);return false;

The bigger difference you try and maintain in a greenhouse between inside and outside temperature the heating costs increase disproportionately since heat is lost to the outside quicker due to the increased temperature differential.

[iann]

My greenhouse has already been to -2.5C (27.5F) this winter. It barely got any lower than that in the whole of last winter, but usually a few nights will be well below. Perhaps a third of my plants are indoors in various locations because I don't want to freeze them. Some would certainly die, most are just at risk of marking or losing roots. I'd love more cool indoor space, but most of them will hardly ever get below 10C (50F). Even the porch doesn't get close to freezing although it can be hard to judge very close to the glass. I have had ice form on the inside of my double-glazed bedroom window, but only on exceptional nights.

[DaveW]

Mines been warmer at night since I bubble wrapped it Ian. Also being 9ft to the ridge in a 12ft x 18ft greenhouse means the internal volume to glass area to leak heat built up during the day is smaller than with lower smaller greenhouses where the volume to glass area ratio is less. Mine is this drop door version so it can be built with 3ft walls under the staging's, meaning no glass there to leak so much heat:-

Drop_Door_lg.jpg (87.12 KiB) Viewed 1031 times

It's really a pity they don't do drop door versions in the smaller aluminium greenhouses to allow you to erect them on walls up to staging height since I always consider under staging glass of limited use as it often just gets used for storage anyway. Being taller too you can get the shelves higher above the staging's so they don't shade them so much, although you then need steps to reach them.

[Carl_B]

It's my dream one day to have a large greenhouse with a drop door, being tall it's a daily struggle dealing with a low eaves... I have my greenhouse set to 5°c this year and all seems to be going well so far.

[DaveW]

The only trouble with their drop doors Carl (it's an Elite Greenhouse) is they are only just over 6ft high (normal internal UK house doors are 6ft 6 inches high). Being 5ft 11 inches high I found when I stepped over the sill I regularly banged my head on the top of the door opening, therefore had to put a course of bricks under the door sill to stop getting a sore head, which makes a bit of a higher sill to step over but cures the headaches!

[Aiko]

Or just cushion the top of the door opening...