Heating question

[Mandy]

Hello to all on the forum,I have already intraduced myself on the forum if you have taken a look you can see I have added photos of are pond which is going to be turned into my new greenhouse, which will be 12ft be 10ft . At the moment I have a small heater in my 8ft greenhouse, but what heating would you recommend for the the new build and also been new to cacti what temp to keep it at, I also will be keeping succulents as well, thankyou.

[rodsmith]

The size of heater needed will depend on the size of your greenhouse. From the photos, as I recollect, it is quite big. I have two fan heaters; one on permanently that blows air at the ambient temperature and helps to reduce damp, stale air that encourages mould and diseases; the other one kicks in at 5 degrees C. In practice this keeps the temperature at a minimum of 3 degrees C. Over the past few years I have lost an occasional plant in the winter but most have been ok. This temperature would be too low for plants that grow in hot areas with warm night time conditions, eg Melocactus, which need to be kept above 10 degrees C but for the majority of succulent type plants I find 3 deg ok. As regards the type of fan heater, it needs to be powerful enough for the size of the greenhouse. Adverts often state the maximum area that a heater will cover. However, you can pay a lot of money when you may be able to get by with a cheapie. One of mine cost under £10 from Argos.

[Chris43]

As Rod says, it all depends....

The size of the greenhouse, 12x10, presumably single glazed, is fixed. There are two key factors which then dictate how much heating you need. The first is the temperature you want to keep it, and the second is the lowest minimum temperature outside you are likely to experience. Hartley Botanic - probably not a greenhouse supplier you'll use - nice but very expensive - have a calculator on their website - https://hartley-botanic.co.uk/guides/gr ... alculator/

I used to live in Amersham, and several years ago the outside temperature dropped to -18C, just one night thankfully, and I was glad I had put in a second 3kw heater for my 10'x30' greenhouse. It wasn't usually needed, but on occasion it was.

You might see on that Hartley calculator, that they mention clear glass or with bubble insulation. I have found that this certainly reduces the heating requirement, but it also had an effect on my plants flowering ability. Many cacti need good light levels to give them the message to flower well when the time comes, and bubble shading reduces light levels to some extent below even that which we get in our dull winters. Also they don't take into account wind impact on cooling, which I have found to be quite significant, and made me over-power my heating by 50%.

Electricity is better than almost any other form of heating, as it does not affect the humidity in the greenhouse. Your overall fuel cost depends on the temperature you set for your greenhouse minimum, but also on the thermostat you use. Some built in thermostats in fan heaters have a surprisingly wide difference between on and off temperatures, this is called hysteresis apparently. If you aren't using a huge amount of power, it probably won't be needed, but with higher power levels (I use 2 x 3kw heaters) a 1C difference can save a fair bit of money over time and then justify the purchase of a closer tolerance thermostat - around £60.

Hope this helps....I'm sure there are other things, but I think these are the major ones. No doubt others will tell me if I have missed something big.

Chris

[Mandy]

Thank you for your replys, i will be going with an electric fan heater and in winter I'm thinking of bubble rap to help with costs. One good thing is the walls of the greenhouse are double with inserlation between. Would you leave the fibreglass on in the inside walls as this was a pond to stop damp coming in or would this be a problem. What do you think!

[rodsmith]

Thank you for your replys, i will be going with an electric fan heater and in winter I'm thinking of bubble rap to help with costs. One good thing is the walls of the greenhouse are double with inserlation between. Would you leave the fibreglass on in the inside walls as this was a pond to stop damp coming in or would this be a problem. What do you think!

I assume the fibreglass is clear or clearish but even so it will have the effect of reducing the amount of light that enters the greenhouse. Using bubble wrap as well will reduce light even more. I think you've got to weigh up the saving in heating costs against the possibility that insufficient light will reduce the probability of flowering. In the end, it's your decision.

[Mandy]

I no what you mean about the light I can remove the fibre glass underneath it its rendered so I could paint the walls white to lighten it up and then just bubble rap the glass in winter that's all.

[Cidermanrolls]

I recommend you buy a good quality electric heater. The hysteresis on the thermostat is important for costs and a heater designed for use in a wet environment could just save your life. Don't stint is my advice.
For insulation. Take a look at twin wall polycarbonate. For years I used bubble insulation but will never, ever, go back now I have seen the huge benefit of a more permanent insulation solution.
Also, think about a dehumidifier in addition to your electric heater. I've been very pleasantly surprised this winter with my experiment with one which has a discharge hose I run outside under the greenhouse door. When you think of the value of plants you might lose to damp......they may appear expensive to run on paper but most of the heat output just replaces heat you'd be putting in to the greenhouse with your heater.......