PC fan to leisure battery

[OldKettle]

Having the door wide open is short-circuiting the ventilation- drier (less dense) air will be wafting in from the top of the doorway and out the vents, the damper air sitting in the greenhouse won't be moving
As a test, leave the door open but fix something over the doorway leaving a narrow gap (50mm) or so at the bottom, get a draught running.
By the way, your fan probably won't do much. Last year had to put an 8 inch extract fan into a tiny timber shed- the control gear was overheating with the 4 inch originally fitted.

Thank you. I will certainly give that a try. The fan arrived today and I have successfully wired it up to the 12V supply, so I am going to give that a try too.

If the door thing works, then perhaps just a louvre vent or two, near the ground would be enough.

Unfortunately, it's not a good day to test the fan (or the door blocking) because it's overcast and the greenhouse is only about a degree warmer than the outside temp (25 vs 24). Typical

EDIT: I also think that I am a bit short on roof vents. I have two 2ft x 2ft vents, but the floor area is 72 square feet. So ratio of about 9:1, whereas I believe the recommended ratio is 5:1

 

[ericmark]

Thank you. The fan should be coming today, so I am going to wire it to the 12V 1.5A supply that I found, just to see what effect it has.

With regards to using a car USB supply to regulate, could I just use a full 12v socket, something like this

https://www.amazon.co.uk/Cigarette-Enisina-Waterproof-Motorbike-Connection/dp/B07BPM1WLJ

You have missed the point, looking at regulating the voltage supply.

 

[OldKettle]

You have missed the point, looking at regulating the voltage supply.

OK thanks. I just wondered if the 12V socket would regulate it (at least regulate it down if the battery was delivering above 12V).