If you want to keep it energy-efficient, look for a system with a heat exchanger (it uses waste heat from a furnace or water heater to heat the incoming air from outside). Otherwise, just sucking in cold air from outside could be expected to raise your heating bill significantly.
Can you provide me a link so I can check out what your describing?
I am worried about noise entering through the duct.
I manage to bring down PM2.5 down within 30 min with 2 large filters and a small one and I also fly screens that apparently block out to about PM2(but also reduce air flow and makes it harder to get air back in to make up for C02) and funnily enough they do work up until the neighbors start heating/using wood fire the smoke just comes straight in. Technically I do what your saying but need to manage it outside the hours my neighbors are using wood fire and it works not a bad way to go about it.
Something like this:
I think these posts are not receiving enough attention. How the heck is the apartment vented right now? If there are exhaust fans in kitchen and bathroom, is there a vent to the corridor when air is being drawn in? Or a gap under the door?
Firstly the corridor is technically outside so that idea is not possible. Secondly, the vents of both the bathroom and kitchen lead to the roof which is the 5th floor. When you say vented do you mean general fresh air or just genral getitng air out? If you mean getting air out then there is an exhaust fan in the kitchen and bathroom and a third which is for a case leak that doesn't have a fan connected its just an outlet. But these vents are 50 years old don't have proper piping and not really sure how there built but they work.
It seems that my soundproof muffled vent idea is just too difficult as someone mentioned a 60cm wall needs drilling and the cost of those muffled silencers seem expensive. However, I can have a filtered fan on the back side which is fairly quiet, this was not my preferred option as it is in the kids room and the wall is near the entrance of the building so people can talk and noise will get through but it is a much simpler option of putting something like the heat recovery ventilation with a HEPA filter that someone linked. If I get noise from that gap then it is what it is.
Fresh air is generally provided by opening the windows but its just a hassle to turn my air purifiers on for 45 min to bring the bad air quality down. And then the carbon dioxide increases back up to 1000 in 30 min, kind of like slamming my head against a brick wall. So I really need filtered air coming in and it looks like I will put it in the back where the sound issue of cars etc is not that bad.
The bathroom and kitchen fans exhaust air out of the apartment. That reduces the air pressure inside the apartment, so air will get pulled in to equalize the pressure. If there isn't an intake vent, then it is infiltrating in through door and window openings, poorly-sealed exterior walls, etc.
Seems to be different over here then. My apartment block with bathroom exhaust fans (because windowless) was built in 1992, and AFAICT there were no special provisions made for these. I generally tilt the closest window while I'm in the bath. When the windows were replaced during major renovations last year, they cut out part of the window gaskets on one window per room to allow for forced ventilation. It's not the most ideal solution since it compromises sound isolation (and needlessly so in the living room which has a pretty much airtight door) and isn't likely to improve the thermal side either, but I guess this is the best they could do under the circumstances. Having your windows replaced while you're living in there was quite the hassle as-is, I don't think any major construction work beyond that would have been very warmly received.
