How to turn a lovley old house with solid walls into a warm efficient home




Good ventilation is crucial to both the fabric of the house and the health and well being of its inhabitants. Ventilation requires letting stale, moist air out of the building and drawing in some lovely fresh air. Unfortunately, this stale, moist air is also lovely and warm, so when it is vented from the building via extractor fans or just idle draughts, we lose warmth into the bargain.

As many of us strive to improve our homes, have doors and windows that fit and seal fully, and block up any potential draughts we are also preventing good ventilation and creating potential problems. I have encountered several people with damp or mouldy walls. They are convinced that they have a rising damp issue when in fact they don't - It is a condensation issue. With reduced ventilation and a modern lifestyle that often includes several people having steamy showers every day the warm moist air has nothing left to do other than condense out onto cold exterior walls and masquerade as rising damp.

I decided to install a whole house Mechanical Ventilation Heat Recovery System (MVHR). The unit draws moist air from 'wet' rooms such as bathrooms and kitchen, and pumps it outside. It also draws fresh air in from outside. The clever bit is the heat exchanger where is transfers the heat from the nasty stale air into the fresh air. In doing so the two air streams do not mix, so the system pushes warm, fresh air into all the living spaces in your home. With an efficiency of 90% or more and low energy motors running the fans, an MVHR saves money over the alternative, which is bathroom extractor fans and trickle vents that simply pump the warm air outside. You also gain a home that has a constant supply of fresh air that is often also filtered - great for those that suffer from asthma.

domus, ducting, heat recovery, eco, house, homeSuch systems are now gaining popularity, so I suffer the burden of choice. The heat recovery unit, which is often situated in the loft, is connected to each room via ducting. Particularly in a retro-fit project, finding somewhere discreet to hide such ducting is the major issue, especially when you are fussy like me. Many of the heat recovery units achieve the same specifications, so the system with the most convenient ducting was likely to win my order. When it comes to ducting, it appears there are two choices. Traditionally, ducting is a mix of 125mm round and 204mm x 60mm rectangular. The ducting feeds from room to room in turn - one duct feeding all the rooms with fresh air and another duct extracting from all the 'wet' rooms. The ducting comes in set lengths and needs fixing together with appropriate bends, tees and joints. The ducting can be either plastic of metal. Because the ducting comes in rigid sections it is necessary to make many joins. This can be fiddly, and it's important that the joints are good and air tight.

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An alternative is to use 75mm ducting. This is supplied in long coils and is reasonably flexible. This means that there are no joins to be made. However, because the ducting is smaller and can carry less air it is necessary to run a separate duct to each room individually.

The next article details my installation of the system.


© Christopher Thompson