Extractor fan specs?

[homertimpson]

I need to have an extractor fan fitted to a part converted garage to obtain a "letter of comfort".

"" A mechanical extract fan is required in store capable of an extract rate of 3 air cycle changes per hour and ducted to the external air""

Could someone put that in plain speak for me please?

i.e. does 'mechanical' mean an electrically opereated fan or is it simply a hole in the outside wall with a fan/vent?

Regards

Homer

 

[felix]

First you work out the internal volume of your garage. This will be easy if it's a cuboid otherwise make a rough estimate of average length, width and height. Three air cycle changes per hour means you have to shift three times that volume you just calculated every hour.

You now have something in cubic metres per hour, or cubic feet per hour if your house was built in feet and inches. It doesn't matter as long as you're consistent. Don't go multiplying floor area in square metres by height in feet!

Next you start looking at fans. The important detail to look at is air flow. This might be given in cubic metres per hour or cubic feet per minute or litres per second or some other weird and wonderful units. You will have to convert this to find out if the fan is big enough.

Example: Your garage is 4m long, 2.5m wide and 2.5m high so its volume is 25 cubic metres. You need a fan that shifts 75 cubic metres per hour. The fan on the shelf at B&Q says 150 cfm. That's fan speak for 150 cubic feet per minute! Now for the maths:

150 x 0.3 x 0.3 x 0.3 x 60 = 243 cubic metres per hour - so you put it back and look for a smaller one.

Hope that helps.

 

[homertimpson]

Thanks Felix,

the room is 8x8x12ft - so your measurements are nearly exact

Now to get off to B&Q for a cheapo fan.

I'd thought about doing the job myself - could manage the wiring with a bit of help - but cutting the hole neatly would be awkward as I don't have one of those humungus cutters that are required.

Will seek a local quote or two.

Regards

Homer

 

[securespark]

so you put it back and look for a smaller one.

As long as you meet the minimum airflow, thats fine. But you can exceed it too........There's nothing wrong in having 6 air changes an hour or whatever...

 

[ban-all-sheds]

Tip: When it gets to the point that you cannot close the door (or open it, if it opens outwards), and you keep finding animals and small children pinned to the inside grille of the fan, you have gone too far...

 

[mapj1]

You can hire the hole cutters - diamond core drill- might be worth phoning up tool hire shops in the yellow pages and asking fo r a quote.
Much less dusty than chiseling or grinding.

 

[homertimpson]

Thanks for the replies folks,

I'll check out the hire shops for the drill - I'm confident about doing that part of the job. The electrics will probably need a spark.

Regards

Homer

 

[mapj1]

You could just put a plug on it if you have power to the room.

 

[Screwi]

Just watch the power of some of those fans, you could be busy doing something and have your ears sucked off, then try explaining that to your insurance company!!!!

 

[securespark]

Learn something new every day. I've never had my ears sucked off before...