Losing heat through extractor

[davecooper]

I had a new bathroom fitted about 18 months ago and had a new radiator and extractor fan fitted. The fan is about 150mm above the tall radiator/towel rail. I was never convinced that the bathroom warmed up very well and when my wife voiced the same opinion recently I realised that this was probably the case. The previous radiator was smaller but the bathroom was warmer.

I am now starting to wonder whether the problem is due to the extractor being directly above the radiator. Is this likely? We live in a fairly windy part of the country and you can feel the wind drawing air through the fan from inside to outside. I have looked at the possibility of an inverted cowl on the fan or even a deflector plate above the radiator. The other option is to replace the fan with one having some sort of flap arrangement that opens when the fan is switched on, although I cannot find such a fan. The fan is a standard 100mm unit. Any advice gratefully received.

 

[BlueLoo]

https://www.amazon.de/-/en/%C3%98-100mm-Connecteur-avec-Clapet/dp/B07KX8L2D8

 

[Harry Bloomfield]

I have looked at the possibility of an inverted cowl on the fan or even a deflector plate above the radiator.

A radiator shelf, is always a good idea, to help force the warm air, to percolate into the room, rather than straight up.

The other option is to replace the fan with one having some sort of flap arrangement that opens when the fan is switched on, although I cannot find such a fan. The fan is a standard 100mm unit. Any advice gratefully received.

,
There are lots of them, the surprise is you have been able to find one without and well worth having, to conserve heat between uses of the bathroom.

 

[foxhole]

You don’t need to change fan, vents are available which close and cover which reduce wind ingress.

Manrose Flap Vent Brown 125mm x 125mm - Screwfix

Order online at Screwfix.com. HIPS polystyrene. Suitable for commercial and domestic use with 125mm round ducting. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Manthorpe Core Vent Brown 160.5mm x 350mm - Screwfix

Order online at Screwfix.com. 127mm (5"). For ventilating gas appliances and general through-wall ventilation. Max. 100cm² airflow. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[davecooper]

I have flaps on the outside to prevent backflow from out to in which works fine. However, this does not prevent airflow from in to out which will spin the fan at some speed if the wind is strong. I need to prevent airflow from in to out while the fan isn't running. This would have to open when the fan was switched on.

 

[BlueLoo]

Sounds like the vent is just a symptom, not the illness.

You shouldn't be having that much pressure differential tbh.

 

[Harry Bloomfield]

I have flaps on the outside to prevent backflow from out to in which works fine. However, this does not prevent airflow from in to out which will spin the fan at some speed if the wind is strong. I need to prevent airflow from in to out while the fan isn't running. This would have to open when the fan was switched on.

Which is what mine does - It has three sections, which when the fan runs, are opened like a camera iris. The section are moved via the expansion of a wax capsule, the capsule heated by a resistor, when the fan is powered. It opens and closes, quite slowly.

 

[JohnW2]

As a general comment (far from the first time) there is obviously a 'conflict' between requirements for insulation ('heat retention') of homes and requirements for ventilation ("X air changes per hour"). If an extractor fan (or merely an open window) really does result in "X air changes per hour", then that obviously means that, every hour, X 'room-fulls of heated air are removed from the room/house, to be replaced by the same amount of cold air somehow drawn i from outside.

Kind Regads, John

 

[davecooper]

The wind tends to blow straight across the fan outlet which must set up a venturi effect which draws air from inside. This is surprising as the bathroom is pretty well sealed. Not a lot I can do this winter but I may try a cowl outside instead of the flap vent currently fitted to see if this helps.
I am also going to make up some form of shelf or similar to force warm air further into the room

 

[Why Not Indeed]

If you want to get really serious about it, you can get single-room MVHR units that claim 80% heat recovery. Not cheap though, might be cheaper to just keep wasting energy...

 

[JohnW2]

If you want to get really serious about it, you can get single-room MVHR units that claim 80% heat recovery. Not cheap though, might be cheaper to just keep wasting energy...

Yes, I should have mentioned that, but, as you imply heat recovery systems are not cheap, and I personally don't know of anyone who uses them - although the same people often seem to fuss about relatively trivial causes of 'heat loss', whilst happily letting an extractor 'pump out' a lot of heat!

Kind Regards, John

 

[Harry Bloomfield]

If you want to get really serious about it, you can get single-room MVHR units that claim 80% heat recovery.

I have never understood the heat recovery claims, because I make it, at best, 50%. All they can recover without heat pumps, is to recover half of the difference of the incoming air temperature, versus the outgoing. Outgoing 20C, incoming 10C, at best the fresh air warmed to 15C.

 

[ericmark]

We have always been shown the flow of air within the room, so best place to measure the temperature is just before it returns to the radiator, and the thermostatic radiator valve (TRV) gets reasonable close to the ideas. A heat recovery unit

would also help, but over the year the whole concept of heating a room has changed, putting a radiator under a window, or a hot curtain in shops can work, specially with double glazing, gone are the days of single glazed windows in metal frames with condensate catchers to route the water outside.

However there is no one design suits all, biggest problem in the bathroom is a shower in a tube, creating the chimney effect, so moisture distributed throughout the room, the shower cubical needs to seal either top or bottom to stop the chimney effect, or simply don't have a cubical i.e. a wet room.

But we have tried to seal our homes, and then we put in cooker hobs, and vented tumble driers which are pumping air out, that air needs replacing, internal design as well, last house was open plan, originally door at front and rear, opening one door could make other door slam, but when extension built the back door was on side of house, and the breeze no longer slammed the door.

This house the internal doors stop that happening. Also must consider open flues, don't want to draw fumes into the house.

Mother house the wet room was accessed from the hall, so the replacement air was cold, so set hall temperature higher on the programmable TRV just before times when she is due to take a shower.

Every home is different, in this house the problem is the hall cools too slowly, not had that problem before, not lived in a house with three standard outside doors and three double patio doors before, seems likely I will need two thermostat in parallel, but putting down carpets has also caused a huge change, so waiting to see how it goes.

So you need to consider your home, and decide what at a reasonable cost will work for you.

 

[Alec_t]

The wind tends to blow straight across the fan outlet

At a previous house I had a similar problem. A simple home-brew aluminium deflector plate alongside the outlet cured it.

 

[aesmith]

I have never understood the heat recovery claims, because I make it, at best, 50%. All they can recover without heat pumps, is to recover half of the difference of the incoming air temperature, versus the outgoing. Outgoing 20C, incoming 10C, at best the fresh air warmed to 15C.

A counter current heat exchanger can do a lot better than that. Whether domestic appliances are that sophisticated is another question.