I was fortunate to be part of the Auckland Home Show last weekend. Yes, for me this was fortunate because I like that sort of stuff – getting to see what’s happening in the industry and also talking with people about what their concerns are about their homes.
I got the chance to talk to a number of people who are thinking about building or are in the process of designing, and a very common questions was “what’s the best type of heating?”, or “what type of heating do you recommend?”. Sometimes it’s more specific, “should I get one of these heat transfer units?” or “what’s so good about heat pumps?”.
Earlier this year, I did a couple of podcasts about heating, but it’s clearly a very big issue and not always one with a simple answer. But here are some guiding principles.
Matthew Cutler-Welsh’s Home Heating Guidelines
(Note, there are exceptions to these guidelines and I’m not stating them as hard and fast ‘rules‘. So, please feel free to comment/disagree).
1. The most sustainable form of heating is passive
Passive heating means using the sun. Heating a home with the sun is achieved by good design, good insulation and a good relationship between glazing and thermal mass. That is, let the sun shine directly onto concrete or something equally solid and heavy and make sure that the solid, heavy stuff is exposed on top and insulated on the sides and underneath.
For more detailed design information I honestly recommend checking out this great CCANZ booklet. Seriously, check it out. I know it’s only concrete, but these guys really know their stuff and it’s mostly written in plain English. There are even some nice pictures. Of concrete.
In most of the North Island, it should be possible to design a house that needs little or no active heating, if you have the right site. Unfortunately for most of us, our house already exists and retrofitting thermal mass is tricky.
2. The second most sustainable form of heating is wood
A log burner or a pellet fire is the most sustainable heater for New Zealand. We grow trees. We burn them. Apart from the transport required and a bit of huffing and puffing to chop the wood, it’s essentially a closed carbon loop. Granted that making and burning pellets does consume slightly more. But the principle remains.
3. Heat pumps are single room heaters
Unless it’s a ducted system, heat pumps should be thought of a heater for a single room. They’re generally sized to heat the lounge or living room (or bedroom) that they’re in and this is the room that they’ll heat adequately.
True, some installers will put certain models in hallways. Other installers won’t.
On balance, don’t assume your heat pump will heat more than the immediate space of the room that the unit is in.
4. Homes with solid fuel burners are generally warmer than those with electric heating
A large heat pump might put out 8 kW of heat. A typical plug-in electric heater, about 2.4 kW. A modern efficient log burner will be more like 12 – 15 kW and some could even be greater than this. Even pellet fires tend to put out more heat than an average heat pump.
The higher the energy output, the warmer the room is likely to be and so homes with log burners or pellet fires can be very cosy.
5. Your roof won’t heat your home
I’m not going to go into detail here. If you don’t believe me, read this Otago University research about the heating potential of ventilation systems.
Be wary of anyone selling you something that offers ‘free heat‘ and lots of air changes per hour.
6. Water is much better at moving heat around than air is
Ever heard the distinctive sound of a VW beetle or Kombi van? The sound is distinctive because it’s uncommon, and it’s uncommon because the air-cooled engine was a bit a of an experiment. Through perseverance and some innovative design, VW did manage to provide enough air flow to their engine to prevent it from over heating, but no one copied them. Most other cars before and since, use liquid as the primary means of transferring excess heat away from a car’s engine. Liquid is used because it’s so much more effective than air.
The same applies with your home. The good old radiator is a very effective and efficient means of heating lots of rooms. The efficiency of a the whole system does depend on whatever the heat source is, but there are some good options to chose from such as a pellet furnace, a gas boiler or even a heat pump water heater.
So if you’re going to invest in a whole house heating option, consider a system that uses water in radiators or in-slab pipes to move heat around, rather than ducts that move air around.
7. Insulation is always the first step
There’s no point tying to heat your home if it’s not insulated. You’ll just be heating up the atmosphere, and there’s enough of that going on already.
8. Insulation is not heating
Refer to point 7. Insulation always comes first BUT insulating your roof won’t keep you warm by its self. Insulation will allow you to be able to get warm.
If you wrap a block of ice in a blanket, it’s still going to be a block of ice. In fact, it’ll stay a block of ice for longer. So once you’ve insulated, you need to add some form of heating.
As for which type is best? Refer back to point 1!
I hope that’s useful. Please add any comments.