[adri123]

I've made a DIY propagator. 

http://chat.allotment-garden.org/index.php?topic=112086.0

It's now got a door on it.  At the moment when you close the door it's pretty much a sealed unit.  Would it require ventilation?

TIA

Adri

[BabbyAnn]

It would depend on moisture and heat given off by the lamps (might be a cool lamp but fittings can get warm) - condensation on seedlings can sometimes lead to damping off, so you could do with something say on the top, preferably adjustable, to allow for day to day variations

[Goosegirl]

Some ventilation is necessary because there will be some moisture in the compost from initial watering in which will condense on the top of the propagator. As seed and new seedlings don't use much water at all, you need to adjust this by letting the condensate escape so they are not too wet.