im growing in an old building abbout the size of a world war bomb shelter i was wondering instead of buying expensive vent systems could i have a a 15 cm wide tube running into the building so fresh air can blow through into the building, cheers
Is this building "sealed up" or does it have drafts of fresh air? If enough fresh air can get in passively, you only need to worry about an exhaust vent to blow out the used air. I'm not sure how big your bomb shelter sized building is. What is important is how many plants will be using the available fresh air. I'm not an expert on indoor ventilation - so just consider this as general information. A lot of indoor growers like to exchange all the air in thier chambers "several" times every hour, maybe every five minutes, or so. For a big room that's a lot of air! Growing in "isolated" chambers makes good ventilation more managable - it's like just heating one room, instead of the whole house. If you can direct the incomming air directly to your growing chamber then a 15cm (about 6") tube should be good - maybe two of them (just a guess). But you will need a blower to remove the exausted air. If you only use one fan, it is better to blow out the exhausted air and let the fresh air enter passively. Hope this helps, "Cheers!"
Tip- blow your exhaust air through a forced ventilation box (air's forced in through the bottom and up through a layer of compost) before it goes out. It helps cut down smells substantially.