I get asked about heating a lot. What’s best, the most cost effective, simplest, efficient. All that. So this is a collection of my thoughts based on all the various things we’ve tried (and we’ve tried quite a few). So far we have (or have had) –
- Range cooker with a back boiler burning wood
- ‘Multifuel’ stove burning wood (no back boiler)
- ‘Multifuel stove burning wood (with a back boiler)
- Proper wood burning stove (not multifuel)
- Rocket mass heater
- Solar thermal panels (for heating hot water)
- Solar pv and/or wind power dump to an immersion heater
- Wood pellet boiler
- Regular vented hot water tank
- Thermal store type vented tank with an external heat exchanger
- Passive solar greenhouse on south facing wall
All in two houses. A little excessive, I hear you cry? Well we try this stuff out so you don’t have to. Here’s how they all worked out –
Version 1 (Lackan Cottage)- Doric Range cooker with back boiler, thermosiphon (no pump) to a regular vented hot water cylinder. Radiators fed via injector tee from the boiler return. Solar thermal panel heating a separate coil in the tank.
This was the simplest system, requiring no electricity to have a tank full of hot water. Light the fire, you have hot water. The downside was that unless the fire was lit, we didn’t really have any heat to the radiators,and we initially undersized the radiators by a considerable margin. The solar worked well when there was sun but our home made pump station setup wasnt the most efficient, and occasionally overheated, cooking a couple of pumps on the solar thermal circuit in the process. Also the hot water pressure at the taps was woeful, meaning that a shower was out of the question. Baths only.
We also built our rocket mass heater, now gone, which was a great project but a hassle to light with the result that we rarely did, and consequently didn’t use the space in winter. I’ve written about the RMH and taking it out here. It was great when it worked.
Version 2 (Lackan Cottage) – A Wellstood Range cooker with back boiler, thermosiphon direct to a gledhill thermal store with a heat exchanger. Unlike Version 1, the hot water goes straight into the tank. You get hot water by passing cold mains water through a heat exchanger that gives you instant hot water at mains pressure. Solar thermal using a bought pump station replacing the home made one.
Still the pumpless thermosiphon from the range, but into a better insulated thermal store. Its heat exchanger means suddenly we had mains pressure hot water, so Claire got the shower she’d been craving for 3 years. The downside is that the tank uses its own pump to circulate water through the heat exchanger, so you need power to get hot water, and also presumably the heat exchnger might give up. So this system not so resilient. The new pump station on the solar thermal made it considerably more efficient and less prone to overheating, so we’ve had more benefit from it. Any sunnyish day means we get water up to at least 50 degrees C, meaning less work for the range.
Version 3 (Lackan Cottage) As before but now using the 3kw immersion heater to take excess power from our solar pv and wind. Also we lost the rocket mass heater and replaced with a Jotul woodburning stove.
Even more hot water on sunny days from the immersion, which is powered by a Solar iBoost unit that pulls power from one of our PV arrays. It generally starts by heating Birch Cottage first and then us, but we can switch it to heat only Lackan cottage when the other place is empty. A handy extra boost.
The Jotul stove is amazing. Second hand of course, but works really well, uses very little wood, and has proper secondary burn which means its clean burning and very efficient. Can be lit in seconds, and the consequence is that we use that room all the time in winter now.
Version 4 (Lackan Cottge) As before but with wood pellet stove, and a solar greenhouse on the south side of the building
So both cottages have a thermal store, and each thermal store came with a dedicated boiler coil that we never used. So the 26kw Ponast KP21 wood pellet boiler feeds both cottages using that coil in each one. We got it off freecycle it works perfectly, though the plumbing is a bit fiendish and gave me sleepless nights along the way. We had a spare 220 litre buffer tank and the boiler heated it, with each cottage taking water from that tank over into its own thermal store using a circulation pump.
The benefit – being able to provide hot water to Birch cottage without the occupants having to always light a fire. If its lit for Birch Cottage to have hot water then it makes sense to draw some off and heat Lackan cottage with it. It also drives the central heating in Lackan Cottage. Main disadvantage is the complexity of the plumbing which now spans 2 houses and has lots of different circuits and inputs, so lots of potential points of failure. I got a spare scrap boiler so that we have a set of spare electronics and motors.
We haven’t had any cold weather since building the solar greenhouse, but we’ve had lots of wind, and the buffer it provides to the house behind was very noticable. It has meant not lightig the wood burning stove in our big room at all yet. My favourite thing to have added, and we’ll see how it performs in cold weather.
Version 5 (Lackan Cottage) As before but with a 1500 litre buffer tank.
Now I’d read that you need a decent buffer tank for a biomass boiler, and our 220 litre one didnt seem very big. After all, it wouldn’t take long to use it all if the heating were on in both cottages. So I saw this 1500 litre monster for sale cheap and couldn’t resist. Installing it required a 100 square foot extension to the boiler shed, and a lot of plumbing rejigs but its in. Snags include the expansion of 1500 litres of water as it heats, and the fact that really it shouldn’t be vented. We’re not quite there yet but nearly, and it does provide a lot of hot water when the boiler is turned off. Mostly. To one house. I’ve got some issues to fix with Birch cottage.
Birch Cottage – Version 1
This always had a woodburner with a back boiler heating the thermal store, some solar thermal on the roof (it was given to us and is a bit leaky so needs repressurising fairly often) and we added an immersion dump so that it gets excess solar. It has underfloor heating which if on in the night, tends to cool the thermal store by morning, though you can get a shower out of it usually. In winter, you had to light the woodburner for a few hours each day to heat the hot water. It too has thermosiphon and so its only real weakness is the heat exchanger on the tank.
Birch Cottage – Version 2
The addition of the woodpellet stove freed Birch Cottage from the need to light the woodburner as much, and when it works it works well. Issues with airlocks in the flow pipe from the pellet boiler buffer store have caused problems and I need to incorporate some automatic air valves to let it out. The underfloor heating running from the thermal store (it uses lower temperatures than radiators) results in really nice heating.
We’ve definitely reached ‘peak heating’. We have 4 ways of heating water in each house but currently they all require some power (unlike our earliest heating system) so they’re resilient in the sense that we always have hot water, but not in the fact that they are all reliant on electricity to some degree. The ideal would be the thermal store heat exchanger but with no power requirement or electronics.
The dedicated woodburner (the Jotul) is way ahead in terms of its efficiency and ease of use over the Stanley multifuel burner, and just less hassle than the rocket mass heater. It was also cheaper to buy it second hand than to build the RMH.
Our original range cooker, the Doric, had an internal arrangement so that hot gas ran all the way around the oven. The newer Wellstood just runs it over the top of the oven and so just isn’t as good. Its just bigger.
The giant buffer store may be a step too far unless I can sort out the last of the plumbing issues (mainly that the system is overflowing slightly all the time – probably caused by water feeding from the cold header tank in the Birch cottage as its higher than everything else. Its a long story).
Solar thermal is worth having as long as you take care over the pipework and use a proper pumpstation AND make sure there’s somewhere for excess heat to go so that you don’t cook the system. (ie a dump radiator).
If you have solar PV you’d be mad not to have something to divert excess to your immersion heater. Its a cheapish addition and its simple to fit.
Having a proper south facing greenhouse attached to the house makes a real difference to the heating required, and was 100% worth doing. Wish we’d done it sooner.