Thread: whirly gigs, exhaust fans

The first are called whirlybirds, at least here in brisbane. They cost from $70 last I looked. They rely on convection, they are barely a pump at all. I have 2 in the shed and they are better than nothing for heat but the shed has no ceiling. Cheaper ones can develop bearing noise overtime, dearer seem to be quiet. I would never recommend anyone use them.

Bunnings sell a solar powered exhaust fan that installs like a whirlybird. $130 for the small one. You will need to install vents in your ceiling. I have no idea how noisy.

Conventional exhaust fans like you find in bathrooms are noisy. I wouldn't recommend them in sleeping quarters.

2c

Originally Posted by damian

The first are called whirlybirds, at least here in brisbane. They cost from $70 last I looked. They rely on convection, they are barely a pump at all. I have 2 in the shed and they are better than nothing for heat but the shed has no ceiling. Cheaper ones can develop bearing noise overtime, dearer seem to be quiet. I would never recommend anyone use them.

Yep - Yep and Yep. They do work better if there is a decent breeze blowing but my measurement of the chain flow rates were disappointing (Similar to DCs, basically divide manufacturers spec by two to get closer to reality).

Conventional exhaust fans like you find in bathrooms are noisy. I wouldn't recommend them in sleeping quarters.

Yep agree again. There are some very quiet bath room fans but expect to pay $$$$.
The standard cheapies are around the $20-$30 mark but they have noise ratings of 45-50db (no distance given) when new and get louder as they get older and as they get dirtier.
Our 10 year old Arlec bathroom fan is around 55 db (at 2m) when clean and 58 db when dirty - I would not want to be in a room with it trying to sleep.

Bedroom fans should be ~40 db at 3 m in sleeping quarters - very hard to find.
You could run these exhaust fans on dimmer switches so that they run flat out before lights out but can then be turned down after that sleeping? They won't like being run at too low a speed for too long as they and the dimmer will get hot.

A quieter type of fan to get is a squirrel cage fan which are used in ACs but these are hard to find and/or expensive.

FWIW
Our bedroom AC fan goes from 35dB on low to 39dB on High
We also have an 18" pedestal fan which park in a corner that is quite noisy, 48 db on its lowest speed.
The ceiling fan runs from 36dB on low to 42dB on high.
All measurements take at the bed pillows.

You don't indicate whether it's heating, cooling, fresh air ventilation or all three you're concerned about. To get any worthwhile cooling or fresh air ventilation effect you need the extraction fans up high and the air inlet vents down low on the opposite wall. As Bob has said squirrel cage fans are ideal for this purpose as they can move a lot of air and they're very quiet. The only place you're going to get that type of unit at a reasonable price is second hand out of a commercial installation. Typically they were installed in larger accommodation establishments where they handled the heating and cooling by the circulation of water. They are known as two pipe systems. Some units are floor standing and others are fitted at ceiling height. You need the ceiling mounted type and would use them as air handling units exhausted to the outside, ie. mounted to operate in the reverse of their original design.

If you decide to go this way you'll have to do a bit of chasing around to locate some suitable units and then do a bit of homework on how you're going to mount them. The low level inlet vents will be easy.

The fans out of the indoor unit of split system air conditioners is another possible source but you'd have to build an enclosure to mount them in.

In a previous working life we had numerous small concrete flat roofed huts housing electronic equipment that were only vented by whirlybirds, for them to effective we had to put louvres in the doors to get airflow. So you may want to consider that or vents in the walls so there is air movement.

BobL: Do you have any experience with the solar rood fans ? noise wise?

Assuming it's a cavity ceiling putting the fan on the roof and vents in the ceiling would isolate the noise somewhat but it ultimately depends on just how loud it is and indeed whether there is a cavity in the buildings in question. Also of course they won't run at night anyway so just a vent then..

Originally Posted by damian

BobL: Do you have any experience with the solar rood fans ? noise wise?

Unfortunately no.

Assuming it's a cavity ceiling putting the fan on the roof and vents in the ceiling would isolate the noise somewhat but it ultimately depends on just how loud it is and indeed whether there is a cavity in the buildings in question. Also of course they won't run at night anyway so just a vent then..

On a related manner at the top of our house attic we have a standard 300mm whirly bird at the end of a short 6" PVC duct with a translucent plastic cover over most of the inside entrance to the duct. I have noticed that the cover reduces the noise from the whirly bird that comes back into the attic through the duct. Most of the time the whirly bird is silent but when the sea breeze steps up the rattles start to be audible.

Rather than a whirlybird, I'd try to source a weather-vane type exhaust. I'm sure you know the type: they look like a simple right angle bend with a mohawk on top. A bit industrial, but they IMO they're more effective and have a much longer lifespan.

Where a whirlybird will spin on it's bearing, making noise as it starts to wear, the weather-vane only turns against the wind until the air-flow past it causes a draw. Much quieter. (Unless you're in the middle of a tornado, I guess, in which case lack of ventilation would be the least of your concerns. )

Even with no wind, the weather-vane will allow for much greater air flow from convection as it is much 'cleaner' ducting-wise, with less turbulence.

It's important to recognise that both of these are basically exhausts and you will need inlet vents down low for them to effectively cross-ventilate.


A completely different option would be making & installing a vented cupola. This has the advantage of providing room in which one can hide extra HW such as an exhaust fan or flap w/bimetal spring to close the vent over the cold season, without constricting the roof cavity further. Probably a hard one to slip past the budget committee though...

in the next few months....taa daa I will be the committee