Fan to bring cool air from outside into a hot south-facing bedroom?

[ParentOfOne]

Has anyone installed a wall extractor/fan not to extract air away from a room, but to bring fresh air in from the outside? Something like this: www.vent-axia.com/range/traditional-t-series-wall-models

@PigletJohn do you have any experience with this?

We have two south-facing bedrooms on the first floor (in a house with ground, first, second floor). When it's hot, the north-facing rooms get some lovely breeze at night, but the south-facing rooms never do and always stay much hotter for much longer. E.g. now it is 20C outside, 25C in the north-facing room and 29C in the south-facing rooms.

I'd like to understand if a fan to bring fresh air in could help, and if there is a way to seal the vents in the winter, or if it then becomes too draughty when it's cold.

A fan in the room is next to useless when it's hot because it just moves hot air around - what I need is to bring cool air in from outside.

Thanks!

Open the windows at the back and blow the hot air out the front. If you suck cooler air in where will the hot air in the south facing rooms go?

When there is a cold breeze bringing cooler air into a room, where does the hot air go?

The point is that in those rooms opening the windows does nothing, there is no breeze whatsoever.
Now it is 20C outside, 25C in the north-facing room and 29C in the south-facing rooms.

Maybe an extractor could help? Or do you think neither an extractor nor an intake fan would be much help? I want to add microlouvres ( www.smartlouvre.com/ ) to the windows to reduce solar gain, but I really hope there is something I can do (other than aircon) to improve ventilation and make the room cooler

All you need to do is position a regular fan to face the open window. Try it!

I just open all the doors and windows to create a through breeze upstairs. My house is L shaped so if there is any breeze I catch it somewhere. Have you tried pointing a fan out out the window idea being it pushes out the hot air and cooler air is sucked in from somewhere else.

What is the floorplan for your first floor? You should be able to open windows on both north and south sides and then create a cross breeze…so cool air coming in north facing bedrooms then flows into the corridor, into the south facing bedrooms and then out their windows. You can help that along by putting fans sucking air in on north side window sills and fans blowing air out in south side window sills.

I wouldn’t be punching holes in your walls and installing extractor fans. You’ll lose a lot of energy efficiency in cooler months for the sake of a few hot summer days for something that can be done faster by opening the window and putting a fan blowing air out on the window sill.

Tried that, it does absolutely nothing. A tall tower fan pointed fixed, not rotating, at the window. Zero difference.

How did you get a tower fan on the window sill?!

@Discovereads yes, losing energy efficiency in the winter is one of my concerns.

I have all windows open, including those in a north-facing room which is exactly opposite the room in question, and I also open the skylight in the loft, above the stairs, hoping it helps get some hot air out.

The north-facing room gets a nice breeze in the evening, but there is absolutely nothing in the south-facing room, none whatsoever.

Maybe all I can do is just install louvres or awnings above the window, to limit the solar gain, and buy a portable air conditioner for those hopefully few weeks a year when it's impossible to sleep.

And maybe paint the south-facing wall white?

I meant the tower fan, something like this www.dimplex.co.uk/product/mont-blanc-tower-cooling-fan , is inside the room, opposite the window, and on top of a table.

Shut the loft. Put the fan in the window so it’s sucking hot air out of the room (top half of window even better). Open windows in north facing rooms to let cold air in.

nb if you do this with the lif open you will suck the hot air out of the roof space into the house.

Sounds like your floorplan doesn’t allow for a cross breeze.
So in day, keep curtains, blinds and window in south facing bedrooms closed.
in evening when it is cooler outside than in the south facing bedroom, open curtains/blinds and windows and put a fan pulling cool air in.

Tower fans are really designed for room purification. They aren’t very good at creating cooling breezes. You need the kind of fan that looks like a plane propeller in a cage. You want to get a pretty powerful one.

@Discovereads I already do all of that: I keep the window closed and the blackout blind down in the south-facing room during the day, then open them in the evening when it's much cooler outside.

I understand what you mean by plane propeller fan, but I worry the little one would stick his fingers in it. Is there a child safe version? Or maybe by next year he'll be old enough to understand.

I can try putting the tower fan closer to the window, on a stool, but not sure it will make much difference.

@5zeds not sure I follow: are you saying that if I open the windows in both the north and south-facing bedrooms on the first floor, then also open the skylight above the stairs on the second floor (ie halfway between the north and south facing rooms) then I'd be pushing the hot air of the second floor loft farther down inside the house? Not sure how that would work. Or did you mean something different?

There are mesh covers for them that make them child safe, but not sure I’d trust them tbh.

So the next option is a portable air con unit. These are the size of a large dehumidifier and can be brought out as needed but stored away in cooler months. No permanent alteration to your house needed.

@5zeds is giving same original advice I did on how to create a cross breeze, but unfortunately your floor plan doesn’t seem to be set up to allow for one. Our U.K. houses aren’t really designed with breeziness in mind!

Thank you all for your time. I really wanted to avoid aircon if possible (I have it in the loft, where honestly there is no alternative, it can get to >30C when it's only 24 outside) but it doesn't seem like many other alternatives exist.

I will also try with the louvres and maybe painting the south-facing wall white.

Page 26 of this document from the good homes alliance has an example of the wall brick being 38C while the painted wall is 28C. goodhomes.org.uk/wp-content/uploads/2019/07/GHA-Overheating-in-New-Homes-Tool-and-Guidance.pdf

Hopefully this combination should mean less heat gets in the room from the window and the walls. Although, realistically, when the temperature > 30C, I can't see much of an alternative to the aircon.

The Passivhaus standard should become compulsory on all new builds!

Normally advice is not to open loft hatches/doors as the roof space is several degrees warmer.

If you push air our the front it will flow in from loft (if open) and from back room (with open window) and from downstairs.

if you have aircon in the loft try turning it on an hour before the kids go to bed. Open their doors and hang duvets round the stairs to keep the cold upstairs (if this works you can sort something more permanent later). When you go up to bed shut the cold in your room for a bit.

"Plane propeller" sounds like what I am using - an American-style high velocity floor fan. They get quite noisy but work incredibly at just what you are looking for, suck the hot air out of a room and replace with cold outside air. Through draft helps immensely with this but can also be used without. Like pp, I just put them inside an open window, on the windowsill. They're pretty sturdy so no danger of toppling over. Can't comment on child safety but as you'd typically run them for an hour or two at most (too noisy to keep on all night) i would have thought that can be managed.

Here's a model pretty similar to what I'm using: www.amazon.co.uk/Metal-floor-velocity-chrome-industrial/dp/B07JQQY7LT/ref=mp_s_a_1_4?crid=2Y6X2ZOXTHY0S&keywords=high+velocity+fan&qid=1658361275&sprefix=high+ve%2Caps%2C123&sr=8-4

If you want to actively cool the rooms get air con

I should have given you a bit more detail.

Point it out the window to blow the hot air out, and open a window on the shady side of the house to draw the cool air in

Set up the fan as soon as the outdoor temperature drops lower than that in the house.

There are obviously bladeless fans (eg dyson) but they are expensive

@5zeds , about opening the loft hatch:
my skylight is on the top floor, above the stairs, on the landing, so not in a room, and is completely horizontal. Something like the first picture here: visionarylofts.co.uk/uncategorized/the-right-stairs-for-a-loft-conversion/

I understand you don't want to open south-facing windows in the morning as that would let hot air out, but opening this kind of skylight should let some hot air out.
Worst case scenario, the wind might push some hot air in on the 2nd floor, but I don't think opening that skylight on the 2nd floor will cause hot air to go down from the 2nd to the 1st floor where the south-facing bedroom in question is!

In fact, we noticed that opening the skylight makes the 2nd floor landing much less hot.

As for bladeless fans, that's also a good idea, thank you. But yes, they're pricey! And the cheap knock off get mixed reviews at best

Ah! We have the same set up with skylight at the top of the stairs. I thought you meant into roof space/attic. Yes, open it, ours works better if we open a window on the ground floor (I use the back door) and it creates a draft bottom to top.

i don't think a fan will help. I think you need to allow cool air to enter the house at the bottom (on the shady side) and allow hot air to escape at the top. Natural convection will do it.

If you ever open the front door and the loft hatch on a sunny day, and stand in the loft hatch, you will be amazed at the volume of air rushing through. I leave mine open during hot weather.

hot air does not descend into the house. think convection currents.

If the house is already cooler that the outside, don't ventilate it because this will allow hot air to enter.

Curtains and blinds to block the sun will also help.

As another option - could you get shutters for the outside of your house on the South facing side?

Or solar blinds that block UV specifically?

I feel your pain though. My old house was south facing to the rear and even on a really sunny winter's day I'd have to open the windows sometimes as it got too hot indoors. At least in the winter it wouldn't take long for the cold air to come in!

I now have a East/West facing house and even then my bedroom was over 30 degrees on the hottest day last week.

Houses are designed to keep the heat in and it certainly works in our house. It took a couple of days for the heat to dissipate completely. You could literally feel it radiating off the walls!