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Hello all! We're considering installing dMVHR units in our Victorian ground floor flat in London. We do not have a roof/loft or space in the ceiling to do a centralized MVHR system. The flat is currently very well ventilated with high ceilings and original vents in all the rooms, and we have no damp or condensation problems. We are lucky to have a decent size garden at the back of the flat, overlooking greenery and trees. There is a train that passes behind the garden about 25 meters away. Our living room, kitchen, and bathroom face the garden. However, both our bedrooms face a busy main road (lots of cars and buses) which is 6 meters away. My wife suffers from respiratory issues and is allergic to pollen, dust and mold. All the literature we've come across so far mentions that MVHR systems 'extract stale air from inside the home while pulling fresh air in from the outside'. Given that the air outside our home is pretty polluted we have the following question: If we install dMVHR units in our flat (initially in the bedrooms, and two years later, in the living room), while this may filter out pollen, will it bring in more polluted air, including vehicle emissions or harmful gases from the busy road inside the home? And, if the system is running 24/7, will it bring more of the outside air at a faster rate than the flow that comes through the current vents? In other words, are we going to save on heating bills but increase the pollution in our home? Many thanks!

With the recent interest in air quality hitting the news, plus the TV programme earlier this week on an experiment to reduce the particulates and NOx for one day in the Kings Heath area of Birmingham. (it's still here on iPlayer: https://www.bbc.co.uk/iplayer/episode/b09m2djj/fighting-for-air ) I've decided to see if there's a way to make an affordable air quality monitor/data logger that I can fit outside and see what the air quality is like around here, and what impact things like diesel cars driving past, wood burning stoves, weather conditions etc have on it, from day to day. What's interesting is that there are now some pretty affordable particulate monitoring sensors available, certainly good enough for hobby use. Looking around I've found two or three for around £15 to £25 each, that output serial data in the form of a count of each size of particle, over a time bin. From what I've read so far, it looks pretty easy to just sample the air periodically and plot the concentration of particulates within the size bins over time. As an example of the sensors available, here's a link to one that currently sells on Ebay for less than £17 delivered: http://www.aqmd.gov/docs/default-source/aq-spec/resources-page/plantower-pms5003-manual_v2-3.pdf?sfvrsn=2 Not sure when I'll get the time to build and test a unit, but it would be interesting, both to see how the air quality changes in a fixed location, and, perhaps, to fit one to the car so that I can correlate air quality with GPS position and time as I drive around. I''m off now to see if I can find some equally affordable NOx sensors.