Logburner with back boiler and oil as a supplement. 17 January at 11:47PM in LPG, heating oil, solid & other fuels 7 replies 231 views

ninat

We live in a 4 bed1980s bungalow in the Scottish Highlands. 

Currently we have a 25year old oil boiler on a pressurised system with a logburner in the living room.
We’re looking to upgrade our heating and I don’t think the walls of the house have sufficient insulation for air source, plus the running costs horrify me.
What we do have is 3 acres of mixed woodland -birch mainly with some willow, alder and pine though we’ve recently added maple and sycamore. We manage it quite well with regular planting, are self sufficient in firewood and have been for many years.

I’m thinking we could install a logburner with a back boiler and a new oil boiler, and switch between the two. I don’t mind if the radiators don’t get roasting hot because the alternative with air source probably wouldn’t either. 

We have great loft insulation and our windows are the Saveheat.
Is this doable? If so what logburner would you recommend? 

Apodemus

Sounds do-able, although 3 acres is probably on the small side to be completely self-sufficient for heating in the long-term in the Highlands.   You want to encourage good firewood trees that coppice (or pollard, so that you can keep them above deer-level) easily, so I'd go for more birch and get rid of the alder and willow.   By all means plant a few pines for the amenity value, but it will be a long time before they provide you with useable firewood. Cherry, rowan, hazel and holly, are all good additions to the mix and seedlings are easily available to forage for locally. 

Why anyone in the Highlands would choose to plant sycamore is beyond me!  

Oh, and as for choice of woodburner, nip along to Bonk in Inverness or Greenflame in Grantown and ask for their advice.

thozza

Can't suggest what model to buy, but you can combine the two into the same system so that the heating/hot water will use the back boiler or the oil boiler if the back boiler is off or the two together depending on the setup. 

Two possibilities are using a buffer tank or thermal store with two coils to indirectly heat the CH/HW - https://energysavingtrust.org.uk/advice/thermal-energy-stores/ 

or a Dunsley Neutralizer which mixes water directly - http://dunsleyheat.co.uk/neutralizer.html

Having experienced both, I'd say the first method is more flexible and economical to run, but has a higher initial cost. 

Reed_Richards

ninat said:

We’re looking to upgrade our heating and I don’t think the walls of the house have sufficient insulation for air source, plus the running costs horrify me.

At the moment electricity costs 34p per kWh.  A properly specified and installed AIr Source Heat Pump (air-to-water) should achieve an average COP of 3 meaning your heat would cost you 11.33p per kWh.  

Oil currently cost around 80p per litre and a litre of oil gives you 10.35 kWh of heat at 100% efficiency.  So a new oil boiler that was 90% efficient would cost about 8.6 p per kWh to run.

These figures will be the same no matter how well or how badly insulated your house is.  At current prices an ASHP would cost you about 30% more to run than a new oil boiler.  

Apodemus

Reed_Richards said:

ninat said:

We’re looking to upgrade our heating and I don’t think the walls of the house have sufficient insulation for air source, plus the running costs horrify me.

At the moment electricity costs 34p per kWh.  A properly specified and installed AIr Source Heat Pump (air-to-water) should achieve an average COP of 3 meaning your heat would cost you 11.33p per kWh.  

Oil currently cost around 80p per litre and a litre of oil gives you 10.35 kWh of heat at 100% efficiency.  So a new oil boiler that was 90% efficient would cost about 8.6 p per kWh to run.

These figures will be the same no matter how well or how badly insulated your house is.  At current prices an ASHP would cost you about 30% more to run than a new oil boiler.  

You will be lucky to get an average COP of 3 in the Highlands.  A lot of new houses here have an oil boiler for the coldest parts of the year as a supplement to an ASHP for the shoulder seasons/summer.

Reed_Richards

Apodemus said:

You will be lucky to get an average COP of 3 in the Highlands.  A lot of new houses here have an oil boiler for the coldest parts of the year as a supplement to an ASHP for the shoulder seasons/summer.

You might well be right, you average COP will depend on your average outdoor temperature.  However the points I was mainly trying to make were:

1.  There's a myth that heat pumps require a well-insulated house but it's just a myth.  A poorly-insulated house will be expensive to heat however you do it (short of free wood).
2. Just at the moment, oil heating is likely to be cheaper to run than a heat pump for enough of the year that buying a heat pump would not be cost-effective 

in_my_bumble_opinion

biomass boiler....will do all your heating and hot water. Costs roughly the same to run as oil but you get some that can take logs as well as pellets, which can make it very cheap. There are also some which you can have in a living space (like an advanced log burner).

9K grant from the Scottish government for rural postcodes. That grant can be used for ASHP or biomass, but with your location and house type I would strongly recommend biomass

Apodemus

in_my_bumble_opinion said:

biomass boiler....will do all your heating and hot water. Costs roughly the same to run as oil but you get some that can take logs as well as pellets, which can make it very cheap. There are also some which you can have in a living space (like an advanced log burner).

9K grant from the Scottish government for rural postcodes. That grant can be used for ASHP or biomass, but with your location and house type I would strongly recommend biomass

Quite so.  And like I mentioned above, if the OP is in Highland, then they could do a lot worse than having a chat with Philip at Greenflame in Grantown.  I've yet to buy anything from him, but he has given me really good advice a couple of times and saved me from rushing into an ill-advised purchase.