It was a problem we’d had for a long time. You know, one of those embarrassing problems you don’t really want to talk about because it seems that no-one else has it quite as badly as you do. And even if they admitted they’d got it, no-one seemed to know a fail-safe way of getting rid of it.
I’m talking condensation. Soggy, horrible, mould-inducing condensation – which streamed down our windows most winter mornings and even down the walls rendering them grey with spotted mould and finally caused the plaster to start falling off the walls.
I used to visit friends and study their homes enviously. No-one else had crumbling plaster. No-one else seemed to have mould all over their window frames, their walls, or the insides of their cupboards. But it was something that we’d been battling with since moving into our three-bedroom Victorian terraced house eight years ago.
The worst rooms were those with two external walls – the kitchen and our son’s bedroom – making them very cold. In the bedroom we’d painted the walls with anti-mould paint, changed the ventilation brick twice and even re-plastered in an attempt to stop the mould growing, but it kept coming back every winter.
A friend told me about a special ventilation unit she’d had put in which completely got rid of the damp in her house (so yes, I did finally find someone with the same problem who’d got a solution!) and which also, ingeniously, managed to ventilate without letting the heat escape – a Heat Recovery Ventilation Unit. I followed it up.
Condensation and ventilation explained
David Prince from Abbott Damp Proofing Ltd came round and surveyed our house. Our problem was pretty typical, he said, especially with single brick houses without a cavity wall where the wall was cold and so the warm air condensed on the walls as well as the windows. Mould grows, he explained, when air can’t move and when water vapour builds up in it. So although the air brick in our son’s room was letting air in (and rather expensively letting the warm air in the room out), the air wasn’t actually moving much in the room hence the mould grew in areas where fresh air didn’t reach, like behind wardrobes. And as we were drying our clothes on radiators, cooking and showering every day, and of course, breathing – our house was constantly having moisture put into it, but not having much taken out. We were living in the British equivalent of the tropics without the heat. Now that’s unlucky. And unhealthy.
The answer to our embarrassing problem, said David, was indeed a Heat Recovery Ventilation Unit. He recommended a single unit for the kitchen and an ‘apartment unit’ for three rooms upstairs ducted from a main unit in the loft into the rooms via small, white vents in the ceilings www.dampexpert.com/products/heat-recovery-ventilation.html This would extract air from the dampest two rooms (bathroom and small bedroom) and supply fresh air to the other bedroom, which then gets circulated.
Each unit runs constantly on trickle vent, maintaining ventilation to the house 24 hours a day, but when the moisture in the air builds up the humidity sensor switches the unit to boost. This is usually set at 55 per cent relative humidity – the point at which mould growth dies off and dust mite activity stops, yielding health benefits for allergy and asthma sufferers and indeed, anyone. The precise definition of relative humidity is ‘the amount of moisture in the air as a percentage of what the air can hold at that particular temperature’.
This constant push and pull of ventilation creates airflow through all of the upstairs rooms – even at night when doors are closed (air does of course still pass under doors, David pointed out, otherwise we’d suffocate).
The ducted system recovers less of the heat than a single unit (65 per cent versus 86 per cent. With the ducted system the air loses some heat on the way to the unit (but most ventilation systems lose all the heat, so it’s still a big benefit). It also has the advantage of being silent in the rooms as the machine is in the loft. If you did just want a single unit in a bedroom, a light sensor could be put on the unit so it doesn’t disturb you in the middle of the night.
Easy to install, immediate benefits
So we had the units fitted. The installation took two days and was hassle-free. One of Abbott Damp Proofing’s installers, Craig, came along with an extraordinarily large circular drill which drilled a hole in the kitchen’s outside wall and the single unit – which both extracts and supplies – was fitted into it and covered neatly with a plastic ventilation cap outside www.dampexpert.com/products/heat-recovery-ventilation.html. A small sensor box was attached to the wall a few feet away from the ventilation unit and the electric cabling was fitted into the wall and re-plastered over (mini trunking is an alternative if you don’t want to cut into the walls).
In the loft, two holes were drilled in the outside wall and capped over outside. The main heat recovery unit is actually very small – about the size of a shoe box. This was placed in the middle of the loft and a 10cm diameter flexible ducting run from the unit to the outside walls (this ducting is light and easily moved if you have to lag the loft or do any building work). A heat exchanger in the main unit captures the heat from the outgoing air and transfers it into the incoming air before it’s sent through the vents to each room and we put loft lagging over the ducting to reduce heat loss from the air being carried through the cold loft.
We switched the units on and left them to do their best. The next morning, as if by magic, we had no condensation. After a few days on a particularly cold morning, we had a little condensation on the windows. We adjusted the sensor by 5 degrees and the next day there wasn’t a water droplet to be seen. And there’s been no going back.
But don’t just take my word for it. I measured the humidity in the house with a rather exciting moisture meter before and after the installation to get the dampproof proof, so to speak. Before the heat recovery units the relative humidity on a cold wet morning upstairs (which produced lots of condensation on the walls and windows) was 76 per cent at 17 degrees C air temperature (40-60 per cent is considered healthy and comfortable) and the condensation readings went off the scale (showing the surface temperature was lower than the point at which condensation forms – the ‘due point’ – creating a sodden wall with 30 per cent moisture content). Unsurprisingly this was all categorised as ‘wet’ and set the machine off in a moisture-beeping frenzy. After installation, relative humidity reduced to 54.9 per cent (at 17 degrees C on a similar cold day), and the moisture content in the wall was 9.1 per cent which registered, thankfully, as ‘dry’.
The upshot of all this scientific wizadry? The mould and condensation has never come back. And we’re the envy of a large number of our friends – many of whom it turns out, were struggling with the same embarrassing problem after all.