If you live in a place like London, where it gets hot in summer but many places still don't have A/C, a fan can work wonders.
Here's the magic trick to cool your home down quickly:
During the day your house heats up. In the evening your home is likely warmer than the night air. Many people try to open the window and put the fan close to the window to blow cold air in.
What works much better is pointing the fan out of the window!
I installed a whole house fan in my previous place. Automatic louvers in the attic and a massive blower that I could open downstairs windows, turn the fan on and it would pull air in from the windows, push it into the attic, and out the louvers.
Not only did it quickly replace the indoor air with cooler outside air, it would also ventilate the attic, preventing it from quickly reheating the upstairs. I could run it for 5 minutes and get the desired effect, maybe 10 minutes in an unusually hot spell.
I used the technique I described in eg London, Sydney and parts of Germany. Most of the time, temperatures had dropped quite a bit by 22:00. (But not always.)
That depends on where you live. I used to live in a place where the lows are night were still very warm. Most of the night was too hot. Just before sunrise there was a moment when outside air was worth bringing in - but it was only long enough to cool the air in the house, not the mass of the house itself.
Now I live in a cooler climate. The highs can still get as high in the day, but it does cool of at night - nearly as soon as the sun goes down.
This - create a negative pressure space inside the house. Then open other windows throughout the house to equalize that pressure. By pushing air out one window, you’re effectively creating a breeze from many windows. It’s also easier to push a large volume of air out of a window than to try and pull a large volume of air from outside a window.
This is the last thing you want to do. By creating a low pressure zone in your home humid outside air will seep in through every crack, gap, and uncaulked seam in your house.
Such a system is basically a mold incubator. The correct method is to:
1) have central HVAC
2) have an energy recovering ventilator (ERV), zhender is a good brand.
#2 Constantly cycles fresh air throughout your home and it’s intake is controllable and filtered.
My suggestion was for situations like London or Germany in summer. The air cools down a lot in the evening there, and people typically don't have any A/C there nor humidity problems in summer. The point-fan-out-the-window technique is for rapidly bringing your home down to ambient temperatures (and humidities).
There will be no condensation, and thus no mold, because the ambient night air is above its dew point, and your own walls start out hotter than the ambient air, and they only approach its temperature _from above_ as you ventilate the house.
What you are describing sounds like it might be more appropriate for something like Florida.
In places like Germany or London, people have mold problems in winter, when the walls are colder than the air in the home.
(You can also get mold problems, when you are running an AC.)
The humidity in London is currently 69%. Your indoor humidity should never exceed 60%, and you should target 40%-45%. If you have no way to control this then you are essentially running a mold incubator.
From my travels around western europe I also noticed a SHOCKING number of bathrooms lack any form of bathroom fan, so hot showers spike the indoor humidity and it stays there.
>The point-fan-out-the-window technique is for rapidly bringing your home down to ambient temperatures (and humidities).
Sure, but the goal is to do that in a controlled manner. Every outlet needs an inlet, and that inlet can either be a dedicated one with a filter (via ERV) or cracks, crevices, and air leaks around your house that you can't see. By puling in uncontrolled outside air you risk moisture buildup in those areas that can lead to mold and rot.
>There will be no condensation, and thus no mold, because the ambient night air is above its dew point, and your own walls start out hotter than the ambient air, and they only approach its temperature _from above_ as you ventilate the house.
Unless your interior air is humid, because the house lacks even the most basic form of humidity control. Then those air leak spots cool the area they're leaking in around which then makes condensation from your interior humidity.
>(You can also get mold problems, when you are running an AC.)
Oh for sure. My point is that a house with proper AC, humidity control, and ERV will be extremely resistant to mold growth. It will also feel fresh, comfortable, you'll sleep better etc.
Where do you get your 60% humidity ceiling from? I live in Singapore these days, we currently have 80% humidity (and that's fairly normal). We have much less problems with mold here than in Britain or Germany.
(In Germany, problems with mold were usually in winter, anyway.)
Yes, bathrooms with neither windows nor fans are annoying.
> Sure, but the goal is to do that in a controlled manner. Every outlet needs an inlet, and that inlet can either be a dedicated one with a filter (via ERV) or cracks, crevices, and air leaks around your house that you can't see. By puling in uncontrolled outside air you risk moisture buildup in those areas that can lead to mold and rot.
Eh, the air will mostly be pulled in either through another open window (good), or through the same window you are blasting the hot air out of (slightly less good), because your fan doesn't form a seal.
I don't really see how you are getting your moisture build-up. You only really get condensation on the walls, when your walls are colder than the air.
> Unless your interior air is humid, because the house lacks even the most basic form of humidity control. Then those air leak spots cool the area they're leaking in around which then makes condensation from your interior humidity.
I never heard of anyone having that problem in summer, and never had it myself.
I have no clue where you are taking your worries from.
Yeah can confirm that's doable, unfortunately it's very disruptive since you need to keep light levels down before opening windows and during it otherwise your place becomes mosquito and moth central.
The silver lining is that it will get better eventually since bugs are dying off rapidly but for now it's either eye strain or buying nets for every window.
> What works much better is pointing the fan out of the window!
I just remember: hot goes to cold. So pushing the hot air toward the cold air is more efficient. If that means pushing the hot air inside the home toward the outside then sobeit.
I don't see that it matters much which way the fan is blowing. What matters is the air exchange, which is about creating an airflow.
If you have a multistory house you can open windows at the top and bottom, the warm air will tend to flow out and pull cool air in the bottom. In that situation if you have a fan, it would make sense to have it blowing air in on the lower level, or out on the upper level.
If you have a single level, the fan will just create a slight pressure difference in one direction or the other. You just need to open several windows, preferably on opposite sides of the room, and if you use a fan to pull cool air in that creates a positive pressure inside the room, which will force the warm air to be exhausted through the other open windows. If the fan is blowing warm air out, then the room pressure will be negative relative to the outside, and cool air will be pulled in through the other open windows.
Yes, it's best if you can create an airflow from bottom to top in a multi-story place.
Getting a draft through your entire place is also good.
What I suggest with the fan works, when you can't do either of the two above.
> I don't see that it matters much which way the fan is blowing. What matters is the air exchange, which is about creating an airflow.
The latter explains the former. A simple experiment: sit 2m in front of a running fan, then sit 2m behind a running fan. In front, you will feel lots of airflow, behind you will feel almost nothing.
That's because the fan 'pulls' air in a diffuse manner, but pushes it as a directed bundle.
It's probably equally as effective to put your fan outside the home and point it inwards, or to put it inwards the home and point it outwards. Alas, most people can only put the fan _inside_ their home, perhaps at the window at best. But that's less effective at exchanging air with the outside than pointing it outwards.
> If you have a single level, the fan will just create a slight pressure difference in one direction or the other. You just need to open several windows, preferably on opposite sides of the room, and if you use a fan to pull cool air in that creates a positive pressure inside the room, which will force the warm air to be exhausted through the other open windows. If the fan is blowing warm air out, then the room pressure will be negative relative to the outside, and cool air will be pulled in through the other open windows.
To use your terminology: the fan is better at pushing air in a concrete direction, than at pulling air from a specific direction.
Your results seem rather strange, though. I wonder where the extra heat came from? Thermodynamics say that heat moves from hot to cold places, unless something intervenes.
Here's the magic trick to cool your home down quickly:
During the day your house heats up. In the evening your home is likely warmer than the night air. Many people try to open the window and put the fan close to the window to blow cold air in.
What works much better is pointing the fan out of the window!