18 Jan 2008

Space heating: where are we headed?

How should we heat our homes? How do we provide comfortable living spaces for people without burning up stupid amounts of energy in so doing?

There is an engineering-type solution to this problem. It’s encapsulated within the Passive House standard. Lots of insulation, triple glazing, air tight like you wouldn’t believe: in short, the house as Thermos Flask. In order to keep the residents alive and healthy, you must have a whole house ventilation system, with added heat recovery so as not to waste a drop of heat. If things turn chilly, you are allowed to fit the odd supplementary heater, either added onto the ventilation systems or something like a wood-burner. By doing all this, you can minimise the space heating energy demand. Really minimise it, although not quite eliminate it. In theory, you can reduce space heating energy requirements so much that they trail in a poor third place behind the other great energy guzzlers, hot water and electrical appliances.

Trouble is that what you have created is akin to being on an aircraft: you live and breathe in a capsule and your comfort is controlled entirely by mechanicals. We know it works because we can survive the worst that Ryan Air can throw at us: besides, people have lived like that in Canada for decades. OK, it makes them a little strange, but survive they certainly do.

The question is would anybody choose to live like this in the UK? And even if they did, would they actually save as much energy as the theory makes out? These are important questions because the way our energy roadmap has been formulated (it’s the Code for Sustainable Homes – again!) we won’t have any choice in the matter. As we live in a relatively mild climate, our traditional response to feeling stuffy is to throw open the window. If people continue to do that, it makes triple glazing look a little bit silly, especially if you are someone who likes to sleep with their windows open a little through the night. Maybe the fact that your house doesn’t have a traditional space heating system will be enough to discourage you from this profligate behaviour, but equally well, you might care about this so little that you go out and buy a bunch of electric convector heaters to keep the temperature up to par.

The thing is that we just don’t know. Mechanical ventilation with heat recovery has to date been fitted mostly into flats with noise issues – where opening windows is a no-no — or by enthusiasts who buy into the idea. Even there, I have visited selfbuilders who have shelled out good money for a system and then don’t use it, often because the fans are themselves a little too noisy. Code Level 6 – what we are all being told we will have to achieve by 2016 — effectively makes whole house ventilation mandatory.

That is quite an experiment. Whilst the theory of mechanical ventilation is well understood, whether it will work in practice and whether people will interact with it in the prescribed manner is still a complete unknown. In Montreal this weekend, the forecast temperature is going to be —14°C: in London it’s +12°C. In Montreal, I would want mechanical ventilation; in London, I am not sure. And yet, as things stand, we are committing ourselves to spending £400million (at £2,000 per pop) every year on it.

Don’t you think it would be a good idea if we were to build and monitor a few thousand airtight homes to see what happens before we roll them out as a national standard? Thus far, we haven't completed one.


  1. Quick question now that all new buildings have to be air tight (and getting more and more so as we move to code level 6) will carbon monoxide alarms become mandatory in the building regs?........

  2. Mechanical Ventilation.....so what happens when it breaks down?

  3. You fix it, obviously.

  4. yeah right

    and in the real world

  5. Given that it's a no-moving-part heat exchanger plus one or a few fans I'd have thought there are not many ways it could fail: air leaks, clogging up or motor failure. All should be pretty simple to deal with.

  6. The problem isn't that MVHR is difficult to fix. Rather, it's not obvious that it's not working, or that it's not working correctly - it needs to be balanced. Plus fuel poor households will be tempted to turn it off, just to save money on the cost of running the fans.

  7. anyone know about carbon monoxide alarms?

  8. These aren't zero-heat homes. The heat is coming from the woodstove or the electric heaters. People should make this clear and stop misleading customers.

    Most Passivhaus dwellings the other side of the Channel aren't heated this way anyway. They have a precisely-controlled gas or oil boiler, electric heat pump or sometimes a wood pellet boiler.

    Many woodstoves are an own goal as they emit more greenhouse gases than an oil-fired boiler. Source for this is surveys by the US Energy Administration and work by Swedish academics, who tested the emissions from different appliances.

    Also many present UK homes are full of energy-inefficient appliances, which may supply as much waste heat as a small heating system would put out. Replace these by A++ energy-efficient appliances, which emit less heat, and the actual space heating energy input needed by the dwelling doubles or triples, making the words "zero heat" seem a distinct misnomer.