[mashbintater]

I've been looking at the ultimate range (Junior 4) of greenhouses on the Norfolk Greenhouses website. I've also read the thread on this site regarding choosing a greenhouse, and the need for a vent window.

I've never had a "proper" greenhouse before so this may well be a daft question. Can anyone enlighten (sorry!) me as to how effective those panels would be in comparison to a vent window?  Obviously there wouldn't be a through breeze. Thanks in advance, Mash. 

[mumofstig]

I have an 6 X 8 Ultimate and part of the back polycarb panel slides up and down for a window opening.
Leave the door open a tad and the back window open a tad and you have a through breeze

[Kristen]

I have simplistic views on this, hopefully others will speak up if I am being daft / ill-informed.

I think on a large greenhouse ventilation is largely by "convection". The hot air rises, and exits the roof vents. There is no forced-breeze, and the plants are not stressed.

The smaller the greenhouse, the more difficult this is to achieve, and it becomes increasingly necessary to reduce the sunlight (e.g. by "painting" the greenhouse with a whitewash type material) and maximise the ventilation - by opening doors and vents to create a through draft.

On a poly-tunnel (which has no roof vents) this is either opening the doors at each end, or (if fitted) rolling up one side to let the air in.

So my view is that the smaller the house the more important that vents are, otherwise the plants will overheat.

The problem with using ventilation to create a through-draught to reduce temperatures is that it stresses the plants more than convection does - a bit like a breeze on your skin evaporating any sweat / moisture. This means the plants have to drink more in order to be able to respire more ...

An additional cooling measure is to "damp down".  Putting water on the floor reduces the temperature because the act of water evaporating reduces the temperature (if my O-levels memory is correct its the "latent heat of evaporation"). This also has the benefit of increasing the humidity - which in turn means the plants are not having to respire as much.

Bottom line: The more vents you have the more options you have for cooling. You don't have to open them all, all the time!

[mashbintater]

Thanks mum, it doesn't mention a "window" at the other end on the website. I liked both the look & the price (£129) for the junior as the size is good for the best position on my half lottie   .

You really took me back to my physics / biology lessons of yester-year Kristen  . Thankyou both very much!

[VirginVegGrower]

I've been looking at the ultimate range (Junior 4) of greenhouses on the Norfolk Greenhouses website. I've also read the thread on this site regarding choosing a greenhouse, and the need for a vent window.

I've never had a "proper" greenhouse before so this may well be a daft question. Can anyone enlighten (sorry!) me as to how effective those panels would be in comparison to a vent window?  Obviously there wouldn't be a through breeze. Thanks in advance, Mash. 

Auto vents every time but you'll still cook in there in summer.

You could open your door - is it single or double doored?

[mashbintater]

It's a tiny greenhouse with a wide door at the front and a polycarb  panel at the back slides up & down for a window opening

[VirginVegGrower]

I have simplistic views on this, hopefully others will speak up if I am being daft / ill-informed.

I think on a large greenhouse ventilation is largely by "convection". The hot air rises, and exits the roof vents. There is no forced-breeze, and the plants are not stressed.

The smaller the greenhouse, the more difficult this is to achieve, and it becomes increasingly necessary to reduce the sunlight (e.g. by "painting" the greenhouse with a whitewash type material) and maximise the ventilation - by opening doors and vents to create a through draft.

On a poly-tunnel (which has no roof vents) this is either opening the doors at each end, or (if fitted) rolling up one side to let the air in.

So my view is that the smaller the house the more important that vents are, otherwise the plants will overheat.

The problem with using ventilation to create a through-draught to reduce temperatures is that it stresses the plants more than convection does - a bit like a breeze on your skin evaporating any sweat / moisture. This means the plants have to drink more in order to be able to respire more ...

An additional cooling measure is to "damp down".  Putting water on the floor reduces the temperature because the act of water evaporating reduces the temperature (if my O-levels memory is correct its the "latent heat of evaporation"). This also has the benefit of increasing the humidity - which in turn means the plants are not having to respire as much.

Bottom line: The more vents you have the more options you have for cooling. You don't have to open them all, all the time!

Correct on all fronts I would say, however I consider my greenhouse fairly large and I cook in there with two fully open auto vents and a door open in Summer.

[VirginVegGrower]

It's a tiny greenhouse with a wide door at the front and a polycarb  panel at the back slides up & down for a window opening

If the size and price are right for you then you've gone for the right one I would say. You can always use whitewash or shading net - both are in Wilkos - if you have one.

I love my greenhouse - it's where I go to escape!

[mashbintater]

Thanks VVG, it has a shaded roof as part of it's design. I hope to get the small one (Junior 4)  soon  .

[VirginVegGrower]

Thanks VVG, it has a shaded roof as part of it's design. I hope to get the small one (Junior 4)  soon  .

Sounds good - enjoy it. Do you get staging with it as I use all space on mine every Summer - deem it a necessity in my case? What do you plan to grow in there?
Only asking because if you don't have seeds yet, I'll whizz you some of my spares.

[mumofstig]

I hang an old net curtain on a wire on the sunny side of my greenhouse, easy to pull to one side when shading not required, much easier than trying to wash shading off

I don't know if the offer for free staging is still on in the newspapers (try the weekend tabloids or read Gardenersworld in the newsagents and write down promo code )

If not the small staging that I got with mine is cheap and cheerful
http://www.norfolk-greenhouses.co.uk/shop/shop-infopage.php?longref=24~0

[VirginVegGrower]

I hang an old net curtain on a wire on the sunny side of my greenhouse, easy to pull to one side when shading not required, much easier than trying to wash shading off

I don't know if the offer for free staging is still on in the newspapers (try the weekend tabloids or read Gardenersworld in the newsagents and write down promo code )

If not the small staging that I got with mine is cheap and cheerful
http://www.norfolk-greenhouses.co.uk/shop/shop-infopage.php?longref=24~0

Now that is a good idea.