What is the best form of home heating?

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.

  • darren

    Hi Matt,
    I read your article as we are beginning to look at new house designs. Soem things which came to mind were;
    All good advice but you said insulation was teh first step then put it at guideline 7. From a european perspective this has been the major problem with traditional NZ houses. I was surprised to see your advocation for wood as the “best” direct form of heating your home. I don’t know statistics but are you saying that the environmental impact of growing, felling and burning trees is lesser than any other options? Or are you saying that it is the best form of heating your home for other reasons? I can see how growing and burning maybe carbon neutral but aren’t their other factors regarding pollution and environmental impacts that need to be taken into consideration?
    Point 4 about homes are generally warmer with wood burners, I would say could be better described as “homes are generally hotter”. In my time in NZ I have observed a very inefficient practice of feeding a log burner as heat pours out windows, walls and roof. Often this room is baking hot with copious mounts of wood used while the remainder of the house stays stone cold. I would question whether a correctly insulated house with passive heating requires the heat output that a log burner produces. Point 2,3,4 and 6 seem to encourage consumers away from Heat pumps and I wondered why that was if that was your intention.
    In some ways better home heating in this country needs to change a paradigm or a philosophy on how we heat our homes as well as what we heat them with. This is about insulation passive design but also habit and behavioral. Moving heat throughout the home instead of heating one room, trapping heat instead of throwing another log on the fire. I totally agree with Point 5 though.
    Anyway please take these comments as feedback and discard what I am ignorant about or you have no use for.
    Regards Dazzer

    • Matthew Cutler-Welsh

      Dazzer,

      Great to hear from you. You’re absolutely right, point 7 should come first from a design perspective. I only really included it at the end because was more about comparing heaters. Definitely, if you get the orientation, insulation, thermal mass and ventilation right, there’s very little need for heating and the type you choose becomes less imperative.

      Yes, I put wood first because, on balance, it is the most carbon neutral. The best option would be an efficient, ultra-low emission log burner or pellet fire.

      Heat pumps are a very good option for many New Zealand homes, particularly as a retrofit (or places like Christchurch where they’ve made it hard to install ultra-low emission log burners).

      Thanks for the feedback. Great to hear from you. I hope that helps, and let us know if you want someone to look over your house plans.

  • Sarah

    Hi there, we are also looking at building an energy efficient home, and we are working with an architect who has a background in sustainable and passive solar homes. I’m from the UK originally and miss the overall comfort of central heating, so have been thinking a lot about heating for the new house. It will have good orientation, insulation, thermal mass and passive solar features and we will have a log burner which will have a wetback to complement solar hot water. My question is, will passive ventilation (e.g. trickle vents in windows) be enough to balance out the temperature in the house, so we are not cooking in the lounge and much cooler in the bed / bathrooms or would active heat recovery ventilation be required? How do you know without living there? We are in the Nelson region so have a lot of sunshine, but want to be warm in the mornings (when the log burner will be off) through the whole house after a few days of bad weather! Thanks in advance for your advice, Sarah. PS am enjoying listening to your podcasts, very informative.

  • Matthew Cutler-Welsh

    Hi Sarah,

    Thanks for your feedback, and good question. I’m hoping to know more about this next week after I’ve been to a ventilation workshop hosted by Pro Clima! So good timing.

    Who’s your architect? This sort of thing does come down to good design and experience. Thermal performance, including mass and air flow can and should be modelled at design stage. If your architect is using ArchiCad, then there’s a very good package available to them (see: http://homestylegreen.com/easybim). And other 3D drawing packages now have similar capabilities.

    However modelling will only go so far. Good design is both science and art.

    Trickle vents will definitely help cool a lounge room on a winter’s night. As to where that heat goes, depends on the layout. I know of a very efficient home in Christchurch that is easily controllable in both summer and winter by using low windows in the lower storey and a roof window in the upper storey. The ‘stack effect’, like a chimney, can be very effective if you have adequate height.

    I’d like to think that if you have good thermal mass and that this mass is insulated on the outside, and exposed on the inside, then the internal temperature should stay pretty constant. It’s like a big thermal flywheel. However, active ventilation can definitely help guarantee the control.

    In short, it’s not an absolute that you will definitely need an active ventilation system. You could design the house without one. Happy to look at the plans in more detail if you like, and perhaps I’ll have an update later next week!

    • Sarah

      Thanks Matthew, we are working with Peter Olorenshaw and are just at the stage of concept planning. I’m one of those clients that has lots of questions and we are really keen that the house feels great, warm and comfortable in winter without costing the earth (in both financial and environmental terms!). I have had a couple of conversations with our local Eco Adviser too, which has been really useful. Have you had any experience of integrated design, where all the stakeholders (client, architect, engineer, builder, landscaper etc) are all inputting at the beginning of the project? It makes a lot of sense to me! What are your thoughts?

      • Hi Sarah,

        Likewise I’m enjoying listening top Matthews Podcasts (and have been interviewed by him also which you may have heard.) so I thought I’d jump in.

        In our experience Trickle Vents are generally inadequate for two reasons.
        1. They are usually very small (minimum code ventilation requirements only) which means chances are they won’t work well (ie won’t provide adequate fresh air) due to not being optimal for airflow (orientation in relation to prevailing wind, air pressure around the house etc) and because they easily become blocked by spider webs etc.
        2. People very rarely use them as they are intended (ie actually opening and closing them to suit the ventilation needs) and tend to leave them closed all the time (so no use but with unwanted heat loss) or open all the time (so cold drafts when unwanted and also with unwanted heat loss)

        If you want to stick with wholly passive / manually operated ventilation then I suggest you include some “night cooling” vents – ie windows that have a grill on the outside to stop birds / insects flying in and a solid panel on the inside. This way when it is cold you can keep them closed (and not suffer too much heat loss) except when you want to bring fresh cold air into the house and when it is hot you can open them during the evening and overnight to allow a flow of fresh cool air into the house. You still need to manage opening and closing them yourself, but night vents in suitable locations will allow plenty of air flow and they will be much more in your consciousness to operate than trickle vents will be. If you don’t want grilles then you can just use suitable small windows to do the same job but the risk is birds & insects etc entering during the night. This is how we ventilate the office building I work in… and occasionally in summer when people forget to open the night vents the office can be very warm in the morning!!

        Integrated design is great and if you can get a team working well together I think you’ll have a much better project outcome at the end and enjoy the process along the way too! (It’s what we aim for as much as we possibly can)

        Best wishes!

        • Sarah

          Thanks Elrond, our architect has lots of experience of passive solar building, and is putting in eaves, thermal mass etc as appropriate to ensure we won’t overheat! He is also being very patient and listening to our concerns. We are keen to use passive solar, as Nelson has lots of sunshine in the winter and it seems crazy not to use it as the cost of fuel is not going to drop!
          We are thinking of using Magroc for the walls and roof, the slab will be fully insulated and we will have double glazing, although not sure yet what the framing will be. I understand that Magroc is very airtight so if we don’t have the trickle vents I am wondering if our building is approaching the passive house model. Perhaps it should be called a hybrid passive solar passive house! My two concerns are that the temperature of the house in winter when we have the woodburner will be uneven (so the lounge could be much hotter than the bedrooms), and that we might be cold on winter mornings. This is why I was wondering about a HVAC system. Would the heat recovery system be effective in sharing the warmth evenly and ensure it is warm in the winter mornings? Would we need additional heat to supplement the woodburner and passive solar gain? However, if the building isn’t completely ‘passive house’ airtight, then is HVAC effective? It’s important to weigh up the cost of installation, and running costs in the years to come as well. Perhaps none of this is necessary and I am overthinking the whole thing……
          Regards, Sarah

          • Elrond Burrell

            Hi Sarah,

            Firstly let me say, I am just responding to the general questions you posed on here and I don’t want to start offering specific suggestions that set you in conflict with your architect. I also have no idea of the specifics if your project so my comments are very general. You are employing your architect and should in the first instance take up all your queries with him so that he can do his job for you in the best possible way to meet your needs. So please take my suggestions as information to feed into your discussions and certainly not any attempt by me to step on your architects toes as it were.
            So, here are my responses & thoughts to your comment & queries
            – seeing as your architect is designing to avoid overheating they should be able to provide evidence or workings illustrating how this is a achieved, perhaps computer modelling as Matthew suggests in his podcasts. It is in your interest to see this and understand how the design is intended to work and if it will suit your needs & lifestyle or if you are adaptable to it. (When you use the fire, when you open windows etc).
            – I don’t know what magroc is sorry
            – the slab being insulated is definitely good. I suggest you find out how much insulation is being used, if it is continuous & unbroken under the slab (if its broken eg by a ground beam or piles, that could lead to cold spots in the floor) and what surface temperature you can expect to experience on the floor. It’s not just about reducing heat loss but also about indoor comfort.
            – passivhaus requires that the building be airtight to 0.6 air changes per hour and that this be verified when built by a blower door test. Without this the building is unlikely to get near to passivhaus performance and comfort standards. Typically air leakage is through material & component junctions rather than the materials or components themselves. Junctions therefore require careful detailing and your architect should be able to show you a detail for every junction of the airtight fabric in the building. ***This only applies if there is a specific air tightness requirement in the project though and you may not have this.***
            – for comfort and performance it is worth asking how thermal bridges are being designed out. A thermal bridge is where something non-insulating interrupts / passes through the insulation (eg a timber stud in a traditionally framed house). In passivhaus all thermal bridges need to be designed out or calculated to allow for – they can be a source of significant heat loss in a well insulated building and may cause cold spots, condensation & mould
            – if your house is well insulated and reasonably airtight, the heat from the wood burner should spread though the whole house. Cooking, showering, using a hair dryer and any physical activity in the house (eg vacuuming) will all help heat a well insulated & airtight house! There also shouldn’t be much heat loss / temperature drop over night. If this isn’t the case then I wouldn’t describe the house as well insulated or airtight.
            – HVAC = heating ventilation & air conditioning. I would never recommend this in a house. HRV = heat recovery ventilation, MVHR = mechanical ventilation with heat recovery, both of these mean the same thing: a low speed fan (quiet, not draughty) providing fresh air into the building that is pre-heated using the heat energy of warm stale air being extracted from the house. I don’t think it would make that much difference to the distribution of heat around the house but it might help a little. It would provide constant fresh air when it is too cold outside to open windows. It would also help the house be warm & fresh in the morning provided the house is well insulated and airtight! For MVHR to be properly effective the house needs to be airtight to at least 1.5 air changes per hour (measured at 50pa pressure) Below this MEV (mechanical extract ventilation) may be a better option. It draws stake air out of the house & relies in windows, trickle vents & ‘leaky fabric’ to provide fresh air. There is a good podcast on “House Planning Help” on ventilation that covers these aspects.
            – the running costs of heat recovery ventilation are very low (its effectively just a low speed fan after all) and more than covered by the savings made on heating… In a passivhaus! In a lower performance building this may not be the case.

            I hope this helps and your project develops fruitfully with your architect & design team.

            Best wishes, Elrond

        • Sarah Whittle

          Hi Elrond, thanks for your most recent response, for some reason I can’t reply to it directly, so have to reply to an earlier post of yours. Thanks also for the information on the differences between HVAC and MVHR, and the general effect they may have on a house, I have been doing lots of research and couldn’t find the parameters of air changes per hour at which these systems are effective. Magroc is a structural insulated panel system, a new product in NZ which hasn’t been used in our region before, hence the questions and asking for opinions. Our architect is fantastic, he has been to visit the MagRoc factory and is doing a great job of our design. He is passionate about eliminating thermal bridging. As we are hoping to only do this once, we want to make sure we get it right, and wish to be as informed as possible for our discussions. Thanks again, Sarah

          • Hi Sarah,

            No problem.

            I’ve looked up Magroc since and understand what it is. SIPS are very good for insulation, thermal bridging (reduction) and airtightness. There are other questions perhaps on the environmental and sometimes structural side of using them. If your house will be built with SIPS walls and roof and good quality windows/doors then I would hope your architect is also including fully designed mechanical ventilation system with heat recovery as your house is likely to be reasonably airtight and relying on trickle vents and/or opening windows is a big risk to indoor air quality (high Co2 levels mainly but other potentially noxious off-gassing from indoor materials also) or if you do open windows enough for adequate ventilation (even in the depth of winter!) there will be considerable heat loss from the open windows.

            Much more detailed information on the thermal mass / Passive Solar Design side of things can be read here: http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-thermal-mass (an article Matthew flagged up on twitter incidentally)

            Best wishes, Elrond

          • Lots of good links to other “Related Articles” on the left hand side of that article I linked to in my previous comment also.

  • Hi Matthew,

    I think it is worth clarifying that this is a substantial difference between “Passive Solar Design” and “Passive House” design (“Passivhaus”).

    Thermal mass is much less relevant in “Passive House” design.

    “Passive Solar Design” unfortunately has a long history of suffering overheating problems (too much glazing facing the sun) and under ventilation problems combined with cold drafts!

    I know a lot of people in NZ still promote “Passive Solar Design” unfortunately this is rather behind the times compared to elsewhere in the world where many people who previously supported “Passive Solar Design” have since realised (or suffered directly) the over heating / under ventilating /cold draft issues and concluded that the only way to achieve genuine comfort all year round in the most energy efficient way is using the “Passive House” design methodology.

    • Matthew Cutler-Welsh

      Elrond,

      Good points both in response to Sarah’s question and regarding passive solar vs Passive House.

      Shouldn’t good ‘passive solar design’ take both summer and winter conditions into account though? I would expect a good passive solar design, by definition, to include decent sized eaves and other measures appropriate to the location in order to avoid over-heating. Or am I just being naive?

      • Elrond Burrell

        Hi Matthew,
        No I don’t think your being naive, a good designer who knows what they are doing with PSD should take summer & winter conditions into account and appropriate eaves or shading would be included. The trouble is that suitable shading for summer solstice (ie maximum summer solar gain) will not provide much shading at other times of the year and at the other extreme, suitable shading for the whole 3 months of summer starts to impinge on solar gain at other times of the year when it is wanted. So the issue arises with attempting to maximise beneficial solar gain while at the same time control / limit unwanted solar gain. Traditionally internal heat gains have not been adequately accounted for – maybe because the PSD buildings weren’t insulated as well as they could be and the fabric wasn’t made properly airtight. However, once you have a well insulated building maximising solar gain and you start cooking or doing some physical activity inside it will get very hot… Which probably leads to opening a window and in turn leads to draughts.
        I should clarify that I’m referring to buildings using PSD principles to attemp to need no other source if heating – ie maximising energy efficiency. Buildings making some use of PSD combined with another source of heating are less of an issue as the solar gain can be more controlled/limited.
        Ventilation is the other issue with PSD because radiant heat from thermal mass won’t provide much comfort when it is battling against cold draughts!
        Regards, Elrond

  • I thought this would be a good reference for the HSG community Matthew –

    Excellent myth-busting guide to radiant heating:
    http://www.healthyheating.com/Radiant_Mythology/Radiant_Floor_Heating_Myths_.htm#.UaR_aWRASmA

  • mcutlerwelsh

    That’s great, thanks Elrond. Always keen for a bit of myth-busting!
    MCW