Tropic 2000 greenhouse heater

I would get an accurate digital thermostat, which costs about £50, and plug your heater into that (and set the heater to FULL). A good quality digital thermostat will control the temperature to within a degree and save a lot of "fuel" compared to the cheap thermostats in low-end heaters, which can overshoot a target temperature by anything up to 10C, which is very expensive, or undershoot by 10C which will kill all the plants

I reckon the cost of a good thermostat will be saved in a couple of seasons.

For example Bio Green Thermo 1 Thermostat available for £39.95 here:
BioGreen Products

I agree with kristen, do not rely on a cheap thermostat they are hopeless.

Kristen, the link takes you to a heated cable, which is not actualy a thermostat that you can plug a heater into.

Due to the vagaries of a green house, draughts, size etc, IMO spending money on a top class thermostat would be a waste.

A plug in type thermostat will only measure and react to the heat levels in its immediate surrounding, so if at low level the GH would be much hotter at bench level or hotter still in the apex. As an example sit in your lounge at a comfortable heat then get a pair of steps and check the temperature at ceiling height.

My solution is to have a thermometer actually at bench level where my seedlings are and over the period of a couple of days adjust the heater thermostat to give me the level of heat I require. Even a cheapo stat on an electric heater is quite adequate for this purpose.

Just had a quick check and the stat range on the OP's heater is plus or minus 2' which will be quite good enough.

You have to scroll down the page I'm afraid. Their site doesn't have individual pages for each product; glad you pointed that out though as others may well miss it

The thermostat is just below the frost protection cables:
BioGreen Products

EDIT: Actually that's a soil thermostat, the normal heater one is a few products lower down still "Bio Green Thermo 1 Thermostat"

A fan heater will even out the heat in the greenhouse, and the thermostat can then react to that. It will turn off the heater long before a cheap thermostat, on the heater itself, would react. (A non-fan heater would take much longer for the heat to "circulate")

The one I linked to has a remote sensor (on a 1M cable) so can be placed adjacent to the plants / on staging etc.

If you go that route I recommend putting a logging thermometer in there, or sitting in there on a cold night, when the heater comes on frequently, and reading / recording from one (but you'll need one that adjusts quickly enough) to check that the heater's thermostat isn't overheating the greenhouse by several degrees before the thermostat cuts out.

I used an online Greenhouse Heat Cost calculator based on a 10 x 8 glasshouse and assuming an average winter temperature of 5C

To heat to 10C would use 243kW hours per month
To heat to 15C, just 5C more, would use 591kW hours per month - 2.5x as much

At 17p / unit that's the difference between £40 and £100 per month.

hence why I think an accurate thermostat is important, and that even at £50 it is likely to pay back in a season or two, although in a mild winter the differential will be less.

The cost involved are substantial and you would need to grow a lot of stuff to make it worthwhile. Might be a lot better to either plant later or buy in young plants.

#7 In your opinion Kristen, I base my observations on my experience as a heating engineer and whilst I agree with some of what you say I would point out that the unit's thermostat as a working range of plus or minus 2'

With the heat lost expected through horticultural glass and loses through cracks, ill fitting doors etc. That thermostat used and adjusted correctly would be OK.

However if I wanted to use a remote sensor I would go for a standard room thermostat say a Drayton with a tighter operating range of 0.6'c at a cost of about £10 plus vat. Wired as an interrupter this would give very tight control.

I have used a temperature logger (USB jobbie that you "setup", place at the monitoring location, and then retrieve and plug in to computer to download the data) and my fan heater maintained the temperature in my conservatory (ill fitting polycarb sheets) to within 0.5C. The thermostat is certainly not sold as being that accurate, but I suspect they are more accurate than their specification, in general, as they have to be "within" it.

I don't have a cheap-ish fan heater (mine has a very accurate thermostat built in, albeit that that would not be near the staging etc.), so I can't easily reproduce a low-cost heater hysteresis experiment.

However, I do have the USB logger, so if anyone has a bog standard cheap-ish electric fan heater and, preferably, an uninsulated (i.e. no bubblewrap) greenhouse [i.e. suitable for an "average worst case for heat loss" experiment] that they are heating I'd be happy to post the USB thingie as I would be fascinated to see the results. Drop me a PM with details and your address.

I would need someone planning to use a heater to do some reasonable work, i.e. not just frost free, so that we see some proper heat / idle cycles, but cold weather is forecast for the next week or two so we have an opportunity for a decent test.

I'd love to see the results from a horticultural student who has tried a greenhouse heater cost comparison for a project ... never found one though, they seem to pitch up on forums saying "I've decided to 'Design a new Spade' for my project, could you fill in this questionnaire please" whereas if they pitched up an said "Recommend me a project" they'd get lots of suggestions! which would actually have practical benefit.

BioGreen Therostat

We have one of those thermostats (controlling a heater to frost protect a greenhouse). It has proved to be reliable and accurate.