hi 40oz here, i was jus wonderin wot fan id need 4 a 2x2.5x5 ft wardrobe with a 250 watt hps in it would i need old air taking out or new air taking in, and can i drill holes in my lamp reflector and suck hot air away ?
thanx 40oz

lti fan or something like that 4" dogs baws ya ya can drill holes and exstract heat and old air from the reflector or from the room intake u could maybe getaway with a couple o flans blowing air in

Check my thread Ventilation

There's your answer, ummm I think.

ive just been to b n q to get some make do fans until i can afford a big extractor, i cut out a hole in the back of my space and it all seemed fine but then i noticed the noise from the fan, i was just wondering when i get my extractor, even if the fan is relativly quite will there be any noise from the end of the ducting as it will just be leading in to my bedroom and not outside and its supposed to a stealth grow.

my make do fan is originally a heater but it has a cool blow function that im using, as this fan is abit beefy, would it be alright just to have a pc or thin osscilating fan as my inlet and a big extractor as my outlet
thanx 40oz

p.s i only have a few cm's between the back of my wardrobe/growroom and my wall

thanx ppl i realy appriciate the help, so im gonna need a 4 incher and some fans blowin in and hole in the top of my reflector with the sucking end of the extractor over it

40oz here, just wondering how to work out the cfm of a fan needed for a growroom, the room size is 2.5wx2Lx4.5h feet or 76wx61Lx138h cm ive got a 250 watt hps in there so it would get pretty hot and also does anyone have a decibel rating for any of these fans,

thanx 40oz

2.5 X 2 X 4.5 = 22.5 cubic feet

Your fan must shift at least that much air every 5mins

= 4.5 cfm

In almost any practical application any fan will not perform to spec. So double it at least.
In fact I would say you want a 20cfm fan at least. Most good 'case' fans will do that.

Probably more important is the efficiency of you passive vents.

cheers mate so does that mean that i wouldnt need a big extractor, because two of these pc fans would shift that amount and theyre stealth ones 20 decibels

overclockers

40oz

PC fans are no good at pushing air through ducting, where were you thinking of moveing your Co2 depleated air to?.

Ventilation is not about cooling its about getting Co2 laden fresh air to your plants.

Cooling is only a side effect of ventilation.

i was thinking of venting from the wardrobe into the room and pulling fresh co2 from the same room, its quite a large room. plus open room doors etc. the heat extraction is quite a big deal for me because its a very powerful light in such a small space(250 hps). i only need a fan that is hopefully below 20 decibels and can do 20 cfm any ideas that can also cool the wardrobe down, any ideas ?

cheers for youre help everyone, more advice welcome

40oz

Hi 40oz;

I have to say that if you use high quality PC fans that are attached to, (and drawing air through) the skin of the wardrobe, then as long as the airflows unhindered, you are only asking the PC fans to do what they were designed for in the first place.

In this instance I would hazard a guess that they would be fine.

When asked to pull air through a duct, (be it 1 inch or 1 foot wide), then the majority of fans lose efficiency, and if you ask a fan to pull air through 3 metres of ducting you can lose as much as 80% of the "design CFM" of the fan, which can equate to a massive loss, (not even worth doing unless the fan is a high quality inline Lti jobber).

But seeing as you have no ducting involved in venting through the wardrobe skin I reckon 2 PC fans will do just fine.

Just remember to make sure the air flow is enough for the fans, (drill lots of little holes), and that any intakes, (passive or otherwise) can provide as much air as the extractor fans require.

Of course, odour control then comes in to play.

Good luck with the grow.

Peace.

RD

I've actually used some of the overclockers fans - for cooling computers - great, for a growroom - total shite! They're actually horribly noisy, and the amount of air they quote is unrestricted flow - with no filtration (which seems rather daft), they might just stop you catching fire,otherwise- they haven't a hope in hell - you need a pukka axial flow, or mixed flow fan (a far more efficient design, that has a lot of "suck", and can overcome the resistance of a carbon filter) - I reckon you'll need an RVK or similar. By the time you've bought a couple of those overcooked fans, and a speed controller, had vat and postage bunged on top, you'd be better off getting a real fan to start with!
People have horribly short memories- only a few months ago, even experienced growers were having massive heat problems - what may (just) work now will be hopelessly inadequate when the temperatures go back up!

My experience of them was not a happy one! - without filtration, two would cool 3x70w hps - just! - the "left over" suck was not enough to ensure an adequate airflow over the plants, or to overcome the most minimal filter - all this is achieved at peak revs - despite several attempts to mount them in a way the vibrations wouldn't transmit to the structure - it does, and they are loud! (even buried in the bowels of the cupboard). Mark 2 was so much simpler - one Soler & Palau tdi60 fan - (£50) sucking through homemeade carbon filter - almost silent! - (have to stick my head under the lights to hear it - it keeps 2 enviros and the cupboard cool, just running on the slow speed setting (its a 2 speed fan) - lots of airflow over the ladies......bags in reserve for the hot weather
seriously, by the time they add all the extras, those bloody pooter fans work out about £14 a throw, then the speed controller, another £15 - you've bloody near spent £50! -then you've got to source a 12v psu or similar
I reckon if growshop owners were honest, they'd sell you the biggest fan they could - it'll do your grow more good than any other single component! - thinks stiff breeze, not sargasso doldrums!

thanx i dont know what id do without this website
40oz

does any one have any wattage information about the s&p or lti fans or a list of the amount of juice they each soak up because im rather worried abot the leccy, ive been told that fans use a hell of a lot of electricity

40oz

I will try and explain the reason for ventilation again.

Most of a plant is created/made from carbon dioxide Co2, a gas mixed in the air, the natural level is about 330 to 340 ppm.

Chlorophyll the green material in the leaf is the bio-lab where light, water and carbon dioxide are combined to produce a simple sugar called glucose. This sugar is the fuel for every plant process and also forms the basis of the plant compounds we are striving to produce. 95 to 98% of the dry weight of a plant is made by photosynthesis, while just 2 to 5% involves soil minerals, cannabis bud is round 2 to 3%, i.e. when you burn an ounce of organic dry bud, the ash that remained would weigh just 0.7 grams, this residue would consist of potassium, calcium, phosphorus and other soil minerals.

This means that the remaining 27.65 grams were made from the Co2 the leaves took from the air.

As the Co2 in the air around the plants drops below 330ppm photosynthesis slows! At about 200ppm it virtually stops, this mean the plant is not growing at all.

Rooms in most modern houses have a complete air change every 3 to 5 hrs. A grow box in a room like this, drawing air from the room and discharging back to the room will soon bring the Co2 of both the grow box and the room below 200ppm.

This means you may only get the equivalent of 2 or 3 hours growth for every 12 hrs you have the light on. The more light you have the more Co2 is needed.

If the Co2 levels get below 100ppm the plants metabolism also starts to shut down, the amount of water the plant can pump slows, parts of the plant can over heat, leaf damage can occur and finally the plant will wilt.

Why do people not think about this? Its not complicated. They will spend money on a bigger light, special nutrients, but the thing that the plants are mainly made of gets ignored.

For plants to grow at the rate they should they need constant fresh air.

With smaller lights this means a complete change of air in the grow box every 5 minutes. If the air is changed at this rate, the discharge air extracted will never be more than a few degrees above the fresh air being drawn in.

As I said the reason for extraction is not to reduce heat. But if the exchange is at the correct rate to supply the plants with the Co2 they need then the grow box will never even get warm.

With any light above a 250w 20 complete air changes or more is better ie at least one every 3 minutes.

Dear oh dear, I'd shoot that advisor if I were you - in comparison to lights, fans use bugger all electricity! From memory, my td160 draws less than 40w! (less than half the average light bulb!) And before you run away with the idea that the sort of current you'll be drawing for a small grow is going to be noticed, or frantically expensive - that's a myth too! (I once worked out a 250w burns about one and a half p an hour!) In contrast, immersion heaters draw simply vast quantities of power, as do cookers, fires etc.etc

I think its 35w on full speed so it would cost £3.53p for ten weeks continuous running at 6p a unit.

40oz you had 5 topics about the same thing fans! I have merged them into one topic/thread.