wall vent question

[Roger Van Zant]

Hi all....

We moved into a mansion and there are two vents in our living room. i found a similar image online and attached here.

My question is...is there any way for me to reduce the amount of freezing cold air coming in? I can push on the vent cover and it "closes", but still more air seeps in from the vent that way. Maybe that is a problem? I was thinking of covering it up on the outside, at least overnight during the winter, but wasn't sure if that is a good idea. Before this mansion, i lived in apartments in Kyoto and in Tokyo, and they had similar vents, but i could actually push them close and very little, if any, air would come in.

thanks for any suggestions or help!

I have the air vents you posted a photo of. When you push them in to the "close" position, the air comes out even more forcefully and noisily due to the Venturi effect. It's the most stupid thing ever.

It closes to keep the rain out during typhoons. RTFM...



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Yes, I realize this. But it is annoying that even in the "closed" position, you cannot stop cold air coming in in winter, and hot/humid air in summer.

[douglasxwilliams]

I would gladly pay 2,000 yen to see a show a band called

the Venturi effect

Apparently, there is a band called The Venturi Effect.

[Chizakura]

(...)The only reason to get in fresh air in summer is to keep CO2 levels low. (...)

Yeah well, I hope you’re right. What do those pesky Japanese architects know about sick building syndrome and PM2.5 and the superiority of opening windows over 24/7 ventilation systems, eh?

Fair enough - if you live in an old building with asbestos or where toxins are gassing out all the time, then maybe you want to air out constantly (or better yet: get a really good air purifier). Note though that unless you live in the very inaka far from factories and traffic, you'll reduce your air quality because unfiltered outside air is really not that great for your health.

For PM2.5 you deal with it with an air purifier. And guess what: it's more effective to have that air purifier clean your room air when you don't constantly exchange the air with the outside air.

[Chizakura]

We have a pretty airtight home so usually leave a window cracked. My wife's parents' place (that we renovated a few years ago) has heat-exchange mechanical ventilation. Wonderful.

Which solution do they use? I'm curious because there are not so many options in Japan and it's hard to find them.

[Chizakura]

In Hokkaido we crave heat and humidity in winter. It would be ludicrous to open windows just before you go to bed if it's -10 C outside. And silly to let the lovely warm moist air left after a shower escape outside!

The problem is with insulation. If you have really good insulation, fine.

But if you don't, then your structures (walls etc.) will get very cold over the night. If you then have warm and humid air in the room, it will condense at the wall and you'll get mold. And since most homes in Japan are not well insulated...

"The savings from air sealing and insulation work are typically much greater than the small amount of air the fan removes from the home."

This puts my mind at ease a bit. And makes me think the house builders and habitants aren't quite as thick as you think they are.

Sorry to break it to you, but you have to decide: do you crave heat and humidity or not? Because if you run your fans on 24/7 then they will *definitely* remove more humidity and especially heat than airing out once in a while. If you don't believe me, get yourself a FLIR and check it in the winter. Or, just check the specifications for your fan and see how much air it moves within one hour.

On top of that, it's less efficient. Why? Thought experiment:

Situation A: you open all windows and doors to exchange ALL air inside. (maybe takes a few minutes in winter) Now you have completely fresh air inside.

Situation B: You open all windows and doors until HALF of the air inside is exchanged. Then you close them. Then you wait 10 minutes or so. Now everywhere in your home you have mix of 50% fresh and 50% stale air. Now you repeat it and again exchange HALF of the air inside and wait again. What's the end result? Exactly, you'll have 75% fresh air inside and 25% stale air.

Conclusion: when exchanging the same amount of air, it makes a difference if the replacement happens slowly over time or all at once. If it's over time (especially with a very slow 24/7 fan) you'll need to pump out a much higher volume of air than when doing it all at once. And since you constantly reheat this air, you lose energy accordingly. (also: reheating happens even with your AC turned off. Most heat energy is in your structures, because those materials can hold much more energy than air. So you will cool down your walls/floor etc. to heat the air, which will can contribute to mold because humidity condenses on cold surfaces)

[Chizakura]

Maybe invest in PM 2.5, CO2, temperature and humidity sensors, then experiment with turning off the 24hr fan and closing the vent.

I live in a 20yo place with none of that fancy stuff. So if I put the bathroom fan on, the air starts rushing *in* through the kitchen hood unless I also open a window. I don't really like the idea of greasy air being sucked into the place, so either have to be cold after taking a shower, or let the bathroom incubate until I go out...

You might want to check for "non-return valve hood" on Amazon. If you can attach that on the outside then you can prevent the above situation. Optimally, you open your wall-vent and make sure the vent has some good filters inside. Then most of the fresh air should come filtered through the vent instead of through your kitchen etc.

[RetireJapan]

Which solution do they use? I'm curious because there are not so many options in Japan and it's hard to find them.

Not sure. We asked the koumuten to find it.

[adamu]

Optimally, you open your wall-vent and make sure the vent has some good filters inside.

I don't have a wall vent. Only windows. But my rent is cheap

[northSaver]

The problem is with insulation. If you have really good insulation, fine.

But if you don't, then your structures (walls etc.) will get very cold over the night. If you then have warm and humid air in the room, it will condense at the wall and you'll get mold. And since most homes in Japan are not well insulated...

It's well insulated. No mold problems at all thankfully.

Sorry to break it to you, but you have to decide: do you crave heat and humidity or not? Because if you run your fans on 24/7 then they will *definitely* remove more humidity...

Wouldn't that depend on the humidity of the outside air vs inside air? Like right now the relative humidity is 74% outside, and 32% inside. Surely the ventilation system will help make the room MORE humid, not less? Of course we can't rely on the system to humidify the house in winter... we use humidifiers and wet clothes as necessary.

... and especially heat than airing out once in a while.

We lose heat, yes. I guess that's the price to pay for having fresh oxygenated air in your house 24/7.

Situation A: you open all windows and doors to exchange ALL air inside. (maybe takes a few minutes in winter) Now you have completely fresh air inside.

Replacing ALL the air will result in the inside temperature being the same as the outside - sub-zero! Can you imagine how much energy it would take to warm that fresh air up to room temperature? Sorry, not gonna happen.

I'll stop there. By the way, you seem to know a lot about this subject. Are you an HVAC engineer?

[Chizakura]

The problem is with insulation. If you have really good insulation, fine.

But if you don't, then your structures (walls etc.) will get very cold over the night. If you then have warm and humid air in the room, it will condense at the wall and you'll get mold. And since most homes in Japan are not well insulated...

It's well insulated. No mold problems at all thankfully.

Must be a blessing of the north then. I guess my reply was more targeted on people living in Tokyo in typical apartments there, it does not apply to cases like yours then. I should have clarified that, apoligies.

Sorry to break it to you, but you have to decide: do you crave heat and humidity or not? Because if you run your fans on 24/7 then they will *definitely* remove more humidity...

Wouldn't that depend on the humidity of the outside air vs inside air? Like right now the relative humidity is 74% outside, and 32% inside. Surely the ventilation system will help make the room MORE humid, not less? Of course we can't rely on the system to humidify the house in winter... we use humidifiers and wet clothes as necessary.

Ah no, this is a misunderstanding on your side. You need to look at *absolute* humidity and not relative one. Basically, if the outside air has 74% relative humidity at 0 degrees celcius (14 degrees fahrenheit) and you let it into your home and heat it up to 20 degrees then relative humidity will drop to ~22%. So less than 32%. So you will make the indoor air more dry. (you can calculate it here: https://www.lenntech.com/calculators/hu ... midity.htm)

... and especially heat than airing out once in a while.

We lose heat, yes. I guess that's the price to pay for having fresh oxygenated air in your house 24/7.

Yeah, without heat recovery ventilation, one has to make compromises somewhere.

Situation A: you open all windows and doors to exchange ALL air inside. (maybe takes a few minutes in winter) Now you have completely fresh air inside.

Replacing ALL the air will result in the inside temperature being the same as the outside - sub-zero! Can you imagine how much energy it would take to warm that fresh air up to room temperature? Sorry, not gonna happen.

Actually, it won't take much energy. Have you ever tried it? Really, heat your home to 20 degrees and keep it like that for a day. Then open everything for just 1 or 2 minutes and close it again. You will see that you'll get to almost 20 degrees indoor room temperature quite quickly even if your AC is not running. If you don't believe it, try it. The reason is that your walls, floor, roof store multiple times the heat than what the whole air in your home can store. To be more specific, one liter of concrete stores 1500 times as much heat energy than one liter of air. 1500! That means to cool down one liter of concrete from 20 degrees to 10 degrees takes 1500 liters of air that is 0 degrees cold.

I'll stop there. By the way, you seem to know a lot about this subject. Are you an HVAC engineer?

No, I'm in IT, but I worked in this field and some of my colleagues where such folks.