Extractor fans and wet roof issues

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lxsw20

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#1660100 28-Oct-2016 23:29

Is there a decent gap under the door? For an extractor fan to work properly it needs to be able to pull in new air and not create a vacuum.

timmmay

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#1660203 29-Oct-2016 08:02

gedc:

Hi timmay. That fan looks like an inline centrifugal fan. They provide significantly more airflow as well as pressure which allows for longer duct runs as well. I think this is the model here or equivalent.

http://simx.co.nz/product-groups/extraction-fans/in-line-fans/high-performance-centrifugal-fans1

I have the SF150S on this page

http://simx.co.nz/product-groups/extraction-fans/in-line-fan-kits/manrose-classic-shower-fan-kits

Your model - if it's the 200mm intake and exhaust pulls 2.5x the air than my current one. It will also cope significantly better on longer duct runs where the inline one will drop performance quicker.

Cheers. Lots to think about. I can get your model from local electrical merchants.

Mine seems a lot bigger. I'll climb up and have a look next time I have a chance.

mclean

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#1660323 29-Oct-2016 10:54

As other have said already, the extract fans will simply stall if you don't let air into the room. An undercut door is OK for small ventilation rates, maybe up to 25 l/s if it's a good fan. For any more than that you need a transfer grille in the door or wall. As a very rough rule-of-thumb you should size the grille with a face velocity of less than 1 m/s to keep the pressure loss down to something that a residential fan can handle.

With two or three heads running for 40 minutes I suspect you will always get some condensation over the shower, but good ventilation will dry it off faster.

timmmay

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#1660367 29-Oct-2016 12:23

We don't have a grill in the door, just a bit of a gap under the door, and air comes in around it too. We have a foot wide dump head, with the fan on low you get a tiny bit of steam or moisture in the bathroom, with it on high, nothing.

I had a look, my fan is Mixflo MF150s, which you can find here. It does 166L/s according to that page, or 127L/s according to this data sheet. If your fan already does 90L/sec and you're getting bad moisture I wonder if doubling it will help much - probably at least a little. You could go for a 200mm fan which can do 280l/sec, but that will move so much air the bathroom will feel cold - my fan on high makes it feel cold. I turn the fan off as soon as I get out of the shower, then turn it on when I leave the room.

Based on these numbers I would look at the air intake for the room like mclean suggested. See if it's better with the door slightly ajar.

gedc

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#1660391 29-Oct-2016 13:06

Thanks heaps for the help guys. Really appreciate it. Opened the bathroom door a few inches today as an experiment - not a huge difference to be honest but I think that is definitely a 'part' of the issue. The fan noise definitely changes when i fully shut the door and then picks up when I open it a few inches. I've also emailed Simx/ Manrose to ask if I go for the pro series inline models or the centrifugal models for the 3 to 4 metre run. Will let you know where we get to with it all in the next few days and will most likely swap out the unit above the shower. Just need to check headspace etc.

I'll also look at putting in a vent above the main door into the hallway so it can suck air in.

Final question. Am I being unrealistic here. The paint on the ceiling is dulux bathroom and is semi sheen. I notice after about 15 to 20 mins a wet look on it from the steam. After a couple of showers ( single head ) it looks wetter. IF we have the double running then we get water droplets hanging off the roof over the shower after 25 mins.

I've been into the ensuit which has the usual heat/ light/ extractor and realised it's also dulux paint on the ceiling but it's flat as in no sheen. I'm wondering if the semi sheen paint is showing up the moisture on the ceiling more in the refurbed bathroom.

Cheers again for all your help

MikeAqua

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#1660399 29-Oct-2016 13:18

We had the extractor in our en-suite replaced because it wasn't keeping up.

The HVAC guys said the ducting was too narrow. They said increasing the diameter of ducting is the best way to increase airflow.

We still only have one fan but it does a great job. The mirror doesn't even fog any more. Also open the window just crack after we have finished in the shower. No condensation anywhere.

Mike

timmmay

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#1660407 29-Oct-2016 13:31

Ceiling paint is usually matte so it doesn't show imperfections. Ceiling being a bit damp doesn't seem like a problem, so long as it clears, and is the right paint.

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gzt

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#1660414 29-Oct-2016 13:47

The paint (and hopefully your ceiling lining) is specified to handle it.

If the moisture is removed by fan action after a short period then it's not much to worry about.

A little bit of temperature does help a bit with the process. For this reason I use an incandescent in the ceiling fan extractor and as a light source. Without it, in colder weather, condensation forms and pools on the inside of the light enclosure to an alarming depth. They should not be designed to operate the fan without the light Imo. That's not the problem here but anyway...

Incandescent lighting and a heated towel rail can improve a problem bathroom no end. Adds about $10 per month to the power bill but often worth it in maintenance saving and healthy house benefits.

Also, warm dry towels last longer : ).

Edit: Heated towel rail usually 60 watts. Equiv to 1.5kw per day approx 37 cents per day. Adding a midnight to 6am timer would pay for itself in a year.

shk292

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#1660415 29-Oct-2016 13:54

mattwnz:

You can get a lot of mold growing inside the shower when you seal off the shower like that. I wonder if it is an insulation issue with the ceiling being too cold? I wonder if there is any insulation in the ceiling?

The dome doesn't need to seal the shower off - in fact, the recommendation is to open the door approx 20 minutes after showering and leave it open. What the dome does is to prevent the mixing of warm damp air and cold dry air during the showering, which is what spreads damp through the room

But, it sounds awkeard due to the central shower head

webwat

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#1664013 4-Nov-2016 21:55

The centrifugal fans generally have more pressure rating and don't stall if the duct is undersized, so I would say worthwhile anyway. However a higher pressure fan will compete with your smaller fan if they go through a Y-joiner into an undersized duct, so perhaps the solution is to upgrade the new fan to a centrifugal, remove the original fan and replace it with an intake vent direct to the ceiling rather than putting a new vent in the door. You are right, the amount of air actually extracted equals the amount of fresh air that replaces it. I guess this means the fresh air could be cold in winter...

Time to find a new industry!

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