vents in a greenhouse

Hi everyone
What a great forum I have enjoyed reading all the posts they have been very informative.
I was wondering if you could help me with a problem that i am having with ventalation in the greenhouse i love to garden and this year after a fantastic year last year growing flowers i have decieded to try to grow veg along with my flowers. This will be my second year gardening.
last year i bought one of those automatic window openers but i don't think it is letting enough air in if i leave the door open my seedling might die as anyone any suggestions thanks.

 

Hi veglady,
You can never have enough vents imho,especially if you are not using fans.
You will need to exchange the air in the greenhouse year round to replace co2 as well as for humidity and temperature control.
The amount of vents depend on the size/type of greenhouse, but 20% of the floor area is a good minimum.
A mixture of roof and low level ones is best so you have a good height difference between them (more height=better passive airflow).
Roof vents usually open first to release hot air in the roof,followed by the low level ones.

Ventilation is also very dependant on the direction of wind outside the greenhouse as this drives the airflow in a passive system.

Fan assisted ventilation (inlet and exhaust)is a good idea for temperature control in summer and it adds another option to the vent system as a whole.

 

how can anyone follow that! but I'll try - the one prob re open doors is what comes through it - poss cats, who can use any open earth space as a litter tray. It's good to pour water over your central path in greenhouse on hot days - increases humidity and reduces temp (a sort of wicking) - enjoy gardening!

 

Thankyou for your advice It looks as though I will be installing electic this year.
I used paraffin as aform of heating but found the smell to much. so I was toying with the idea anyway for heating the greenhouse I never though about fans to help ventilation thanks again.

 

The best heater/fan I found, was one from Two West's - greenhouse suppliers. The fan is powerful, and with a thermostatically controlled heating element. You can operate them seperately. This winter, I have had it on the fan coming on when the heater comes on - but you can have the fan on alone. Pricey, but so far worth it over the cheaper models you can get in the garden centres.

 

The electric fan blower I have used for some years is one under the brand HOTBOX you can get differing sizes to suit you g'house size, ideal for thermostat heat and air circulation in winter months, or just air circulation in summer.
will edit this when I find suppliers info, this may be the one Fran is talking about!

 

http://www.twowests.co.uk/TwoWestsSite/product/HBFH.htm
I guess this is the one everyone's talking about - I've been looking for one too, and am glad to hear one recommended.

 

Very interesting and thanks Fran and Nixonf23. Quite expensive. But I note that the lowest temperature setting is 6C. This will cost more to run than one with a setting of 1C or 0C if you just wanted to keep the frost off.

 

I've got a frost-free heater in at the moment from B+ Q - it wasn't very expensive - sorry haven't got a suitable link at the mo

 

Thanks again everyone for your advice it is all welcome to a newbie like me.

 

I have a Parasene make (electric) 3kw heater you can pick up in most G Centres it has the option of having the fan on without the heating, we paid about �£25 a couple of years ago, it also has a frostguard setting & is very cheap to run, we have a 10x6 Greenhouse insulated with bubble wrap, for the last week we haven't let the temp drop below 10c inside & with the temp outside being bitterly cold its cost us just over �£2 to run for the week

Helen

 

Gardening Newbie - that seems pretty good. I think if you are going to heat you must also insulate. How have you kept the temperature at 10C, is the frostguard a proper thermostat, that you can set? and how do you know it only cost �£2 - do you have a power consumption meter?

 

That`s about 10 hours worth (3kw) of constant heating for the week which is quite good.

About 3.5p per sq ft of floor area

 

Yes I have a power consumption meter which is very good (Maplins)
Basicly you have to play with the settings on it for a couple of days (the heater that is!) the thermostat is numbered & I have found leaving it on No4 it does not drop below 10c & the top temp is 13c but get your self a min/max themometer & try it on no4 & see what it drops down to, I've just had a look at them in the garden centre this morning & they are around �£40 for the 3kw version, I certainly would recommend them, when it eventually breaksdown I am going to try one of the gas types as propane gas is very cheap to buy & we can get it delivered free

 

I use a small window mounted kitchen extractor fan on a timer to ventilate my 6 foot square greenhouse. Having another one to blow air in as well is a good idea. I wish I'd thougt of that. The roof vent leaks so badly that I've had to put a polythene flysheet over the whole thing to keep the rain out for the winter.
I think I'll seal the roof vent completely, add the second fan and operate them both via a timer and a thermostat for the summer heat.

Nik