Automating radiator based heating system

Our house has a radiator heating system, fired by a large Marshall wood burner.

I’m looking to improve this heating system to achieve:

  • some level of heat storage – so that we don’t have to run the wood fire whenever we want heat
  • a way for that storage to stay reasonably warm for 4-5 days, so we can go away and have the heating automatically run before we return home
  • thermostat control on the individual radiators so we can hold a temperature, rather than adjusting temperature through how vigorously we stoke the fire
  • zoning of the rooms, so that those rooms not in use can not consume heat
  • allow me to run the boiler hard, rather than damping it down, which reduces pollution and increases heat output from a given weight of wood
  • the boiler also runs the domestic hot water (DHW) in winter, currently that’s an open cylinder rather than mains pressure, it’s a bit small, and takes forever to get hot water to the kitchen
  • the thermostat on the boiler that controls the pump is slow to cycle, leading to the boiler overheating and boiling the water, rather than heating it. This is wasteful of heat.

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On global warming

So, whilst on holiday and pondering the future somewhat, it occurred to me that it’d be nice to register for posterity my current views on some things.  The main point being to put a peg in the sand at a point in time and say “I think x”, and to come back in the future and view that to see how your views have changed over time.

I thought I’d start with my views on global warming.  If you’re here for the technology stuff, I suggest you don’t read this – it doesn’t relate to technology.  🙂

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Solar hot water, hydronic heating

I’ve been interested for a while in getting underfloor heating, probably of the hydronic variety.  Underfloor heating offers some benefits in terms of less air movement and noise, and of giving a more liveable ambient heat – there is some evidence that the warmth of your feet is a key determinant of how comfortable your house is in winter.

The concept has been to use a large water storage tank as thermal mass, and to use evacuated tube water heating to heat that tank.  This gives most of the benefit of having large thermal mass in your house, whilst giving control over when you take the heat out of that thermal mass.

This blog post explains why I think that’s probably not a great idea anymore, and what I’m thinking instead.

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Remote walls and thermal bridging from fasteners

When reviewing the search terms that people visit here with (yes, I know, kind of like egosurfing), I saw a couple of people coming here looking for remote walls and thermal bridging.  And I did recently do some searching and found relevant content.

To recap, remote wall construction is a technique where you leave your wall cavities empty, you sheath the outside of your timber framing, you run an air/moisture barrier over the sheathing, then you put polystyrene over the outside of that (continuous insulation), and finally cladding over all of it.  The advantages are that:

  • your air barrier is moved outside the walls – so you don’t break your air barrier when you install power points and the like, so your house is much more air tight and therefore warmer
  • your insulation isn’t prone to thermal bridging from the studs
  • your insulation is rigid foam instead of batts – not as susceptible to collapsing and giving a lower R-value than you thought

You can combine with a similar system over the roof, giving you a conditioned ceiling cavity to run services in (and avoiding having fibreglass in your ceiling, which is one of my pet hates).

So, one of the questions that goes with all this is how you install continuous insulation, and cladding on the outside, without creating thermal bridging.  The document I found that seems most authoritative is this study.  And I think the conclusion is that the thermal bridging isn’t as bad as you might think, and in turn that means (thankfully) that you can just make your cladding as well attached as you need, and not mess around with fasteners that might not be durable or might not stand up to the wind you might expect.


Solar hydronic heating

So, I’ve been wondering for a while about whether you can mostly heat your house with a (large) solar hot water system, plus a good sized storage tank to bridge you through cold periods, plus a hydronic (under floor or radiator) system.

I’ve been researching some more today, and probably am not a lot closer to knowing.  But what I have learned today I’ll include here, over time I’m going to post some more on this as I form more coherent ideas.

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Super insulated houses – Remote building style

As part of thinking about building a house, I’ve given consideration to building a super insulated house.  In different parts of the world this is called different things, often a passivhaus, named after the German standards.

Once you get reasonable insulation in your house, the main source of heat leakage is through air leakage – cold draughts in your house are a major source of energy loss.  Air leakage is controlled through making the house air tight, which in turn relies on an air barrier.  In most houses, this barrier is the dry wall / gyprock / gib board (depending on whether you’re American, Australian or kiwi).  The trouble with this is that it’s really difficult to keep airtight – think of the opportunities for leakage:

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Wood Burners

I’m quite interested in getting a wood burner with a boiler (or wetback if you’re from NZ – which isn’t a racist term, but rather refers to the water running through a unit in the back of your wood burner).

I’ve looked at wood burners for a while, my observation is that those available in Australia and NZ are really not as good as those available in Europe.  The typical burner down this end of the world is relatively inefficient, puts out a fair amount of particulate smoke (which are very bad for health).

In Europe, there are more interesting units.  I have a lot of interest in this unit from Germany, which is relatively small in footprint, and pushes about 1.2kw into the room, 14.4kw into the water.  You combine these with a water accumulator such as this unit, which stores hot water for a couple of days after the burner goes out.  In theory you could run your domestic hot water and underfloor heating off a combination of these units plus a solar hot water unit – probably evacuated tubes – more about that in a later post.

Having said that, this thread is also interesting, indicating that Australian eucalyptus timber gives issues with resin buildup in a unit not built for it.  It also suggests some NZ made units that could be interesting.  These are more pure boilers than combined fireplace/boiler.  Remember that my better half likes the look and feel of a fireplace in the house, so probably I need something that is a combined wood burner and boiler.

Another interesting point about the German units is that they are sealed – they don’t pull in air from the house, they take outside air into the combustion box, and then vent out the flue.  This should reduce dust being dragged into your house, and also if you’re building a house that is very airtight for insulation reasons, avoid issues with lack of airflow and/or with dragging in cold air from outside.

If I ignore that fact that the better half wants a wood burner, I’m more than half tempted to just go with a heat pump instead, much lower maintenance, no cutting and carting of firewood, no ash to clean.  But it’s not quite as heart warming in winter as a fire in the corner of the room.