24/03/2025
This is a filter I changed in Stoke recently…
The new one is completely white (like this one once was).
After changing, airflow into the home more than doubled - from 0.8 to 1.9 metres per second.
Why is this important?
Like a giant solar panel, our roofs generate thousands of dollars a year in free heating, cooling, and drying. The problem is, half the time it’s useless. But for the half of the day that it’s useful (summer nights + winter, spring, and autumn days), we want to get as much of that air down into our homes as quickly as possible.
Running a fan is cheap - about the same as a traditional light bulb (or two if you have a 2-fan system).
Comparatively, air-conditioners and dehumidifiers are much more expensive to run (roughly 5x more expensive than a ventilation system). We still need some extra heating &/or cooling other than a ventilation system but why not get as much free heating, cooling, and drying as possible first?
Also, when your home is dry, it heats and/or cools faster…
Think of heating up a full jug of water vs. just one cup’s worth or,
How long a fridge would take to cool down a bucket of hot water vs. being “empty” (just hot air).
- Water is much heavier than air and harder to heat or cool.
Also, a dryer home is more comfortable, isn’t it?
Think of being cold but dry vs. being cold and wet.
Or, how much hotter it feels when it’s muggy vs. a dry heat.
Why are our roofs dryer than our homes?
Because inside our homes we breathe, cook, shower, wash dishes and clothes… producing around 20 to 30 litres per day. Extractor fans help. Opening windows and doors can help but nowhere near enough and doing that usually comes with security, comfort, and more bug issues.
By contrast, the air in roofs is simply fresh air from outside - replaced multiple times a day (or hour if your ventilation system is running). Even if it’s raining, air is pulled up under the soffits (leaving the water behind), dried a bit more by the timbers and other materials (which are, later, dried again by heat during the day), and brought in at a good level of humidity (not too dry).
I’ve heard people go on about the questionable quality of the air in roofs. I point out, the air outside is often not much better. Either way, it is important to have a good functioning filter to remove all the nasties yet still let enough air through to make the most of all the free goodness up there.
The cost of regular filter changes pale in comparison to what you get out of a well-functioning ventilation system (especially if you get it for half the usual price).
I’ve also had people try and point out that the free heating and cooling in our roofs are “at the wrong time of day”. Well, there are two things to consider:
Starting point - if your home starts from a warmer place each evening you don’t pay for that initial heating. Likewise in summer, each morning your home can start cooler than it would have been.
Residual heat/cool - think of how much mass (weight) is in your home. It will store heat/cool for days. So, load up on as much as you can while it’s there.
I no longer work for a ventilation company but I still put one in every home I live in and rental property I buy. I’ve personally been involved in over 1,000 installations (and follow-up calls) and I can tell you that, in 99.9% of the cases, it makes a massive difference.
Recently, I saw a way to make installations and filter changes more affordable - offering both of those for around half the retail price. Let me know if either is something you’d like a quote on.
