Running a fan in winter ?

[jimhardy]

hmmmmmm

I still think this thread has veered off subject again

[Ian Cooke]

But is a fan in a closed space such as a garage going to actually do any good other than move around the stale humid air? With ventilation of a greenhouse we are aiming to replace some of the existing humid air, depleted of carbon dioxide with fresh air from outside. The air in the greenhouse will have a high humidity from the water vapour lost by plants in transpiration. In winter we aim to ventilate to replace that air with drier air and so reduce the risk of botrytis. Whether greenhouse or garage I cannot see the point of moving around stale air. Much better would be to have an extractor fan and replace the air a few times a day.

[The Codfather]

Well I topen my garage door every night........Also, there is a window that I could open......this would help to cause a through draft.

[Kristen]

Dehumidifier? or is that completely daft?

[Dave Brown]

But is a fan in a closed space such as a garage going to actually do any good other than move around the stale humid air? With ventilation of a greenhouse we are aiming to replace some of the existing humid air, depleted of carbon dioxide with fresh air from outside. The air in the greenhouse will have a high humidity from the water vapour lost by plants in transpiration. In winter we aim to ventilate to replace that air with drier air and so reduce the risk of botrytis. Whether greenhouse or garage I cannot see the point of moving around stale air. Much better would be to have an extractor fan and replace the air a few times a day.

I kept my polytunnel closed for nearly 3 weeks last December, with just a fan and a 1kw fan heater. If I had left it open I would never have been able to keep frost free as the cooling would have been too much for the heater. I had no problems with Botrytis even though pumping around stale air.

Ventilating only works in conjunction with heating as the air is normally between 70 and 100% humidity outside over winter. If you just let it in it will stay at 70 to 100%. It is only when you heat it the humidity drops.

Particularly with an unheated greenhouse keeping the air moving, will prevent botrytis to some extent.

[The Codfather]

So IYO what would you do in my situation ???? at the moment that garage is averageing at 10c day & night.....the door gets open for acess etc.....

in there at the moments are things like collies, allocasia, ginger, cuttings etc on heat matts in fron of the garage window........there is slow growth....but I notice water is dripping occasionally from the leaves.....I am just to say keeping the soil damp.

[maritimesbob]

I have finally bubble-wrapped the greenhouse and installed the electric fan heater. I tested the fan heater for 15 mins and at it's lowest heat setting, the greenhouse was already holding steady at 18C and the heater was only on for a few minutes as the thermostat shut it off (this was late evening too). The small size of the greenhouse is going to make this an economical pleasure to heat it up.

I try to keep the roof vent open during the day and closed at night but we've had some quite stormy weather lately and I don't want the wind catching the window and ripping it off. Hopefully living down here the heater will be used very little. I have it set to keep a min of 10C and judging by the test run it should be cheap and easy to achieve it. Our lowest temp so far has been around 9C.

Is it worth keeping the blower fan running most of the time and trying to keep some movement of air? I can appreciate what Ian is saying regarding the moving around of stale and humid air, but then I can always open the door a little and use the fan to suck in some outside air?

[valdypiero]

I heat my fernhouse in the winter using a natural gas heater. I run a fan 24/7 otherwise there are cold spots in the fernery where botrytis can set in.

[maritimesbob]

Curious, are most people keeping their greenhouses just frost free or are they aiming for higher mins?

[valdypiero]

Reply to Ian : Yes you are right... in theory, it's better to draw in fresh air but in the winter that is cold air! In my case, because I operate a thermostatically-controlled gas heater I have to allow a little external air in otherwise the heater would not burn properly (there are two penny sized holes drilled in the wall of the fernhouse to let this air in...I find that this is enough). However, because the fernhouse is packed full of plants (see picture in post above) I run an unheated fan as well, to ensure I don't get any cold spots (especially at ground level and in the corners of the fernhouse) which would cause botrytis. This fan is basically recirculating the heated air (I have all the greenhouse vents shut to conserve heat) all around the greenhouse. So by keeping the temperature at a minimum of 10C/50F all winter with the fan running 24/7, I find I can overwinter sub-tropical and montane tropical ferns without too much bother.

[musa_monkey]

I have one in the greenhouse running 24/7 as everything is crammed in there so i want to be sure i get some air circulation.
I also have one in the garage but only run this occasionally and not necessarily daily
as there are more air gaps around the door etc and its a bigger less crammed space

[GREVILLE]

I'm a big fan of these (sorry ) I have a 1kw fanheater with thermostat down to +1c. There is an independent fan only without heat on this which I leave on 24/7 through the winter during frost-free spells.

During milder spells of minima 5c+ and maxima 10c+ the door and lights are opened and the fan is not used and there is plenty of air change.

The greenhouse is bubble-wrapped and successfully keeps out freezing conditions when the heating is put on with the thermostat at +3c. The greenhouse is so jammed with plants in winter that low humidity is impossible. However, I seldom have botrytis problems with this set-up

My draughty garage stores large items temporarily in freezing conditions and makes very occasional use of another 1kw fan heater along with a washing machine and tumble dryer! (sorry, that's not very green of me )

[Kristen]

in theory, it's better to draw in fresh air but in the winter that is cold air!

I saw a Grand Designs program where someone was building their own house and had installed MHRVS (mechanical heat recovery ventilation system) - basically a fan that extracta "damp" air from "wet" bathrooms etc. and passes it through a heat exchanger to heat incoming air which is piped into "dry" rooms.

The owner had installed a large diameter pipe down the length of his drive as the duct for the incoming air so that in Winter it would be warmed by the subsoil (and in Summer cooled).

I wonder if it would be similarly possible to bury an "inlet" pipe for a greenhouse to minimise the heat that needed to be added to bring it up to temperature (compared to just using ambient air), but provided an ample supply of fresh air?