Why we installed a Smart
by Unknown - 17:39 on 27 October 2013
The background
We moved to our house almost three years ago and, from the beginning, we tried to find a better way to heat it than the pre-existing oil boiler - better both in financially and in terms of CO2. The house was built around 1810 and is in the North of Scotland. However, it is in a maritime environment which does not usually go much below zero albeit winds can be high. There is no mains gas supply. The house is a listed building and regulations at present rule out various insulation measures, for example double-glazing (unless the existing windows have already rotted away). The previous owners had been allowed to install a small amount of double-glazing and had put in some insulation. We have put in some extra loft and under-floor insulation and also some secondary glazing. Nevertheless the heat loss is substantial and the building is fairly large. It is around 260 square metres in floor area measured internally or 800 cubic metres within the heating envelope(the ceilings are fairly high). If you measure area and volume to the outside of walls, then you include some thick stone walls and also some cupboards and unheated storage space, then the area is over 300 square metres and the volume over 900 cubic metres (even excluding the loft and cellar). The old oil boiler is rated at 44 kilowatts and the radiator capacity is about the same. My own calculations suggest that this is about right for the heat loss at -10 degrees C. Despite this potential low temperature heat loss, we decided to install the Klover Smart 120 which is about 25 kilowatts gross or 22.5 kilowatts nett. One consideration is that the heat loss is not so great as 44 kilowatts at normal winter temperatures. Moreover, we think we can satisfy even our low temperature central heating needs using the Smart 120 because we have a programmer which can switch on and off different heating circuits within the central heating system and divert the Smart's output to wherever it is needed. The house is divided into the upper-floors heating zone and the ground-floor heating zone.Also the ground floor has a sub-zone, a large sitting room, which itself has a programmed timer. Moreover, in addition to central heating, we have some space-heating stoves. We had the house zoned while we were still using the oil boiler so we have experience of using zones and we never heat the whole house at once. Roughly speaking we either centrally heat the ground floor (dining room, kitchen, sitting room, hall, loo, utility room) or the two upper floors(bathrooms, bedrooms and study). In addition, our three wood burning stoves together have a capacity of about 16.5 kilowatts. Thus our total wood-burning capacity is about 39 kilowatts which is not far off the capacity of the oil boiler.
We believe that in practice the wood burning capacity matches the oil boiler. The oil-boiler is badly situated for heating because it is in a small utility room (it still is there because it is being kept to provide for emergencies and to provide frost proofing if we go on holiday in the winter).When the oil boiler is firing it massively overheats this small room. When it is off the air vent provided for it increases draft up the stairwell if we donot keep the door to the utility room tightly shut. Furthermore, the oilboiler's minimum output is 35kw. This means that the oil boiler provides large surges of hot water which fill radiators before thermostatic valves and/orthermostats switch off. Consequently rooms swing between being too hot and too cold. Another consideration is that the oil boiler has a short modern flue.This means that it does not heat any of our traditional chimney stacks (we have three separate stacks) and also it fails to cope well with north easterly winds which results in a smell of kerosene in these conditions. The oil boiler wasquite expensive to run. Over the winter of 2012-13 we had the central heating on for 9 hours a day, but the house was divided into zones which were never onat once so, on average, rooms were heated for 4.5 hours a day. This used 4500 litres of oil which cost approaching £3000.
Aims
Our aims in installing a new heating system were to:
- meet our needs for warmth,
- provide enough heat in the house to help prevent damp,
- make use of existing chimneys where possible and thereby help to reduce damp in the old stone walls,
- reduce our CO2 output,
- keep running costs as low as would be consistent with our other aims.
A process of elimination
We considered the following replacements for the old oil boiler:
- Condensing oil boiler
- This would have been relatively cheap to fit, at about £4000 all in. However, it would not have led to very significant CO2 reduction nor to much lower running costs (the old oil boiler is supposed to be about 85% efficient, although I doubt if it is in practice, but then I doubt whether a condensing boiler would run in practice at its optimum efficiency either). Nor would we have wanted to position a condensing boiler anywhere other than in our small utility room, so it would not have provided heat in a traditional chimney stack and it would still have generated excess heat in our utility room
- Wood-burning boiler stove
- We seriously considered installing one of these. A problem that we had was that our house had a pressurised central heating and hot water system. Installers understandably insisted that we needed a non-pressurised circuit with a sizeable thermal store to take the heat from the boiler stove if the pumped central heating system switched off. We had a choice between cheap and cheerful system and a more expensive system. The cheap and cheerful option (about £9000) would have been to have a boiler stove in our dining room with a small thermal store to replace our current hot water tank. However we did not want to have our main heat source in our dining room, partly because it is south-facing and often has considerable solar gain even in the winter. A boiler stove elsewhere in the house, where we might have preferred it, would have been much more expensive because of the plumbing runs. It would have cost about £14000, thus about the same as the cost of installing our Smart 120( including the Smart's 4.9 tonne hopper, which is in an outhouse).
- Pellet boiler in external out house
- The utility room where our oil boiler is situated was not big enough for a pellet boiler that would be big enough for the house (indeed the vast majority of pellet boilers would not fit into the utility room, at least not without excluding the sink and washing machine). Also the regulations for a solid fuel flue are different from an oil flue so the flue regulations would also have precluded installation in the utility room. We did not want any other room to be taken over by an industrial type boiler and hopper. So we seriously considered installation in an out house. We had estimates for installation from £17000 to £30000 with kilowatt rating for the boiler 30kw to 45kw) We suspect that these installations would have turned out not to be feasible because of listing building regulations or building standards. Another consideration was that a considerable amount of heat (around 10% so far as we could make out) would have been used in heating the outhouse)
- Pellet stove in a living room
- We did consider this, but we thought that the noise of the pellet stove fan would be undesirable in a living room. We were prepared to consider the Klover Smart 120 because, after going down to Bristol for Stovesonline to show us one in action, we concluded (rightly as it turns out) that its noise would be no greater than existing noises in our kitchen (electric oven fan, kettle etc).
- Air-source heat pump
- We did consider this possibility, but the maximum heat pump size without a three-phase electricity supply being installed was around 16 kilowatts. One installer did try to tell us that a 16 kilowatt air pump would be big enough to heat two floors of the house down to -2C and the third floor could be heated also if a 6kw backup heater were brought into play, but after reading the literature on air pumps we did not believe that the air pump would be adequate at low temperatures. Indeed we did not believe that our radiator system would deliver enough heat at the relatively low water temperatures that even a "high temperature" air pump would provide. Nor is our old house suitable for underfloor heating and it would cost a lot to install it. This installer's estimate was under £12000. Another installer proposed £20000 for a similar system. A third installer told us that a system could be installed but it would only provide background heating for the house.
The RHI scheme
We decided to install the Smart before the government finalised its proposals for domestic funding. We decided to keep our oil boiler to provide heating if we went away for a week or more in the winter, because of the Smart's hopper, and its ash can, being too small to support heating for many days. We did explore the possibility of an auger automatically to supply the Smart, but this would have had to run over 8 metres under the lawn and we were concerned that it might break down. Also, it would probably have been an ugly intrusion into the kitchen where it would have fed into the Smart 120. It was not clear that we would be subsidised for installing a pellet system inconjunction with an existing oil boiler when we installed it, but this iseligible for funding in the government's latest proposals. However if you havea "bivalent system" with a pellet stove and an oil boiler then you need to have a meter installed to measure how much heat the pellet stove feeds into the central heating system. We believe that, without the RHI scheme, the financial justification of the Smart would have been marginal - we think it would have paid for itself in about 14 years. With the RHI scheme we think that it will pay for itself very much faster than that. However, the government's proposals for metering and its requirement that one gets a Green Deal Assessment with a deemed heat output for one's house makes the RHI scheme complicated so I will write a separate posting about that.
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That's all very interesting, Roger, and helpful to those of us considering the leap of faith from kerosene to biomass and, more scary I think, from cooking on a cooker to cooking on the boiler. Thank you. What raised my eyebrow was the thought of the cooker putting out 9kW into the kitchen. I know that when my 8kW log stove is working hard you can't stand near it for more than a minute. It strikes me that if the manufacturer says it can put out 5.2kW, then your assumptions leading to the 9kW figure might (I hope) be a bit out. Considering your estimated efficiency figures, my feeling is that a real world 80% for a boiler in this situation, ie. where it is not working steadily a lot of the time, is good going. I find your story encouraging. If we 'go for it', it will be down the route of the full-blown Green Deal Assessment, deemed output, fixed sum RHI payments, as we have never used anything like as much heat as our Energy Performance Certificate suggests we should. In any case it will give us an incentive to continue being as frugal as we can be, although the running costs will be a lot lower so we would expect to be more comfortable throughout the year. Can't wait! I wonder whether you can perhaps tell the world how you see the possibility of a buffer tank benefiting the system, particularly in a smaller house with a total demand more closely matched to the 22.5kW net on tap. Finally, it would be great if you could please post something specifically from the perspective of the cook, covering the idiosyncrasies of the cooker in Summer and Autumn? That would complete the picture nicely, and hopefully reassure The Boss. Thanks very much. Joe