Recommendation for Extractor Fan

[Arctic_Simon]

Hi All, looking to replace the extractor fan (100mm) in my bathroom. My bathroom is long and thin and the shower is on the opposite side on the bathroom to where the extractor fan is (See attached crude drawing). I currently have the MANROSE CQF100T 100MM installed which replaced a none working one when I got the house, but it seems a bit pitiful and struggles when the shower is running. Does anyone have any recommendations for decent 100mm extractor fans that would be good for this scenario?

Thanks in advance for your help.

 

[stem]

The minimum recommended air flow rate for a bath / shower room is 15 litres / second (Building Regulations Part F) but sometimes more extraction is beneficial especially if the fan doesn't continue to run on for a while after the shower has finished being used. It might be worth investigating the extraction capacity of your existing fan and looking for one with a higher extraction rate when you choose a replacement. Centrifugal fans generate a higher pressure than a basic axial fan and tend to be more effective as they can maintain a good airflow despite variations in external air conditions, they also work well with ducting (more about that later) but they can be bulkier and more expensive.

However, the most important thing is missing from your diagram. For a fan to work well, air should be drawn across the entire room. When air is sucked out of the bathroom, air will come in from somewhere else to replace it. Ideally the source of the replacement air (usually the door which shouldn't be tight fitting to allow airflow when it's closed) should be diagonally opposite so the air flow 'sweeps' through the entire room taking the steam with it as it goes.

In reality it's not always possible to do this when the fan is located in an external wall. So a ceiling fan with ducting to outside can be a better solution.

If for example, you were to have a window next to the fan open, the replacement air would simply come in through the window, and be sucked through the fan and returned to the outside (air takes the easiest route of less resistance) so no steam would be collected from the rest of the bathroom.

Also to be considered is that the fan must be suitable for the location it is installed in. If in Zone 1 (less than 2.25 metres from the floor when installed above a bath or shower) it needs to be suitably rated for such a location (IPX4 as a minimum).

 

[Arctic_Simon]

Thanks for your detailed reply Stem. The spec of the fan says - 75m³/hr, 21 litres per second. I have added some more to the layout (door location and window). There is a window next to the extractor fan. It does have a timer feature which I leave on after the shower. The problem I am having which may not be related to the fan now thinking about the above points, is that sometimes when I have had the shower there is a strip of water underneath the fan on the wall.

I will check if there is any gap underneath the door when I get home that could allow replacement air to be drawn in.

So in this scenario I shouldn't have the window open at all during running? (Sorry i moved from a house that didn't have a fan and just opened the window) I have tried it open and closed and on occasions has this water on both occasions, but not every time. I believe wind hits the back of the house so maybe it is only on these occasions. I have a flap vent fitted on the exterior of the extractor fan. Would i be better off with a different vent cover - maybe cowl vent?

 

[stem]

The shower is a bit to the right of the airflow, but generally the overall layout isn't that bad, (I've seen worse) provided that there is a sufficient gap below the door to allow air to enter at the same rate that the fan is pulling it out of the bathroom. I guess your task now is to determine what's causing the water. The duct from the fan through the wall will get cold and condensation will form in it, so the duct should slope downwards slightly towards the outside so that any water runs that way and not into the bathroom.

 

[Murdochcat]

The key to the extractor are keeping the window closed, having sufficient air flow under the door and an over run timer

Compromise on any of these 3 key points and you’ll regret it

Plus you need heat to

 

[foxhole]

You could add another fan over shower ?

 

[Arctic_Simon]

Thanks guys. I will check if there is any gap under the door when I get home and ensure the window is closed while showering next time. I guess if the duct is straight and not sloping downwards the condensation could be running back in (or blowing back in - I will check if it is windy next time it happens also) and dripping out of the fan, but I also guess changing this is not an easy task, it is solid plastic ducting from the bathroom through the wall to the exterior.

If it is wind causing it to blow back would a different type of external vent cover help at all do you think?

 

[Arctic_Simon]

Just home. Looking at the gap at the bottom of the bathroom door it is very small. A couple of mm at best so might need to take some of that off and see if improves things.

 

[Murdochcat]

Just home. Looking at the gap at the bottom of the bathroom door it is very small. A couple of mm at best so might need to take some of that off and see if improves things.

Try leaving the door slightly ajar to see

 

[Arctic_Simon]

Try leaving the door slightly ajar to see

Ill try a shower with Stanley wedging it tonight

 

[Arctic_Simon]

Ok so the steam did clear nicely with door ajar and there was no pooling of water / condensation in the edge of the extractor fan like i have seen previously (yesterday). I will try this theory again with next few showers and see how it gets on.

If i was to take some off the bottom of the door, what size of gap should be left? 10mm?

Thanks guys.

 

[Murdochcat]

I normally suggest 6mm or 1/4 inch

 

[Arctic_Simon]

Thanks for the advice all. Like i say i will try next few showers with the door wedged and if works i will get to chopping the bottom door