Navitron Renewable Energy and Sustainability Forum

BIOMASS => General => Topic started by: Algy on July 12, 2013, 02:41:46 PM

Title: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: Algy on July 12, 2013, 02:41:46 PM
We have completely gutted and are renovating a house (detached, aprox. 290 sq.m.). There is currently no heating or hot water, or anything. We are not on gas. We are insulating it as best we can.

There is woodland behind us where we can source logs, but are in early 60's and I guess thinking ahead 10 years the amount of physical work for logs may be hard, but we like the idea of using for free the available wood.

We're not looking at solar/heat pumps for a combination of cost and roof aesthetics. But will have to have an oil boiler to provide heat/hot water.

Output is to UFH/Rads/hot water.

However, we have an existing chimney that can be lined for a wood burner and will certainly have that. But I like the idea that if we also have a back boiler on the stove it will contribute to the overall load (even if not replace) the oil boiler.

We would want to have an integrated system and that looks like a thermal-store etc. which would need to be designed and installed.

There are people like Chelmer that design and supply, but not install complete systems, but are quite expensive. There are people who fit woodburners but not oil boilers, the ones that fit oil boilers don't do wood. The ones that call themselves Biomass installers are mainly interested in bigger wood pellet systems.

Finding someone who can advise on the system and install it seems like looking for a unicorn.

I'm at the point of giving up on making maximum use of a wood burner by have a back boiler and just shoving in a dry wood burner to heat one room and mainly running oil.

Is it worth persevering with getting an integrated woodburner boiler/oil system?

Advice and thought desperately needed...

Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: desperate on July 12, 2013, 03:56:59 PM
I would say in view of the amount of work needed to supply a stove that delivers usefull amounts of hot water, you are best going for a dry stove. But carefully consider the design of the heating system so that it responds well to the heat from the stove. For instance you could zone the upstairs and downstairs heating loops seperately each with its own roomstat. If then you leave some doors open so that heat can circulate freely through the house the upstairs heating zone may rarely come on, likewise with the downstairs zone, put the roomstat in the living room but no too close to the stove. You may want to divide the upstairs and downstairs into even more zones so you could for instance have a bit of heat in the bathroom but not anywhere else.

The possibilities are endless really and it is simple to do with just standard 2 port zone valves and roomstats, you really don't need to get too fancy with compensation and electronic setbacks and such like, if a lot of the heating zones are off a lot of the time what good does a really trick control system do for you?

Have fun with it.

Welcome to the forum by the way :)


Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: pigletisno1 on August 24, 2013, 08:31:26 PM
                        I'm having the same sort of problem deciding what system to install, I've decided on having a 10 Kw Merlin wood burning stove fitted and would like it to provide DHW via a thermal store during the winter when the burner is likely to be used most. I have a 4Kw PV system in place and plan to use the summertime excess generated power to supply an immersion heater fitted into the thermal store which in turn will provide DHW.
                        I'm hoping the stove will provide enough heat to warm the house during the winter with maybe some central heating for the upstairs during the coldest months, my concern is whether the expense of running the central heating system via the thermal store will be enough of a benefit and still leave enough heat to warm the rooms via the stove. If it's not worth the extra work and expense I will just install the DHW system with the stove. Any advice is welcome.

                                          Thanks, Dave.

Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: dhaslam on August 24, 2013, 08:52:36 PM
There is a very big saving  in wood by using a  non boiler stove and there is also a   cost saving on capital.   If you spend the cost difference on solar thermal  or PV   or both you would   have  a system that saves  quite a lot of oil or electricity and at the same time eliminate a lot of the work. 

Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: julian on August 24, 2013, 10:43:44 PM
I think you need to get the thermal store sorted, with enough inputs for your possible future uses.

I dont know about costing, but i would not have thought that adding another coil for
  • would have that high a percentage price increase.

Once this is situated, if you consider pipework.  You can even lay the pipework.  Before the house is rebuilt, the trouble will be minimal.

That way you keep your options open.

I think you are right to have an oil boiler.  There are times when you just want to flick a switch.

A dry stove will burn more efficiently than a wet one.

The cost of heating DHW from an oil boiler is not huge.  Its space heating that costs so much.  This may be a real consideration for you?

We have all three (&solar tubes)- but most are not in use yet.  It will be interesting (for me) to see how the options compare.

Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: brackwell on August 25, 2013, 10:59:12 AM
My approach is to keep it simple and to not go for clever intergrated systems.

At your age you should not make yourself reliant on wood in any shape or form. There is a lot of work in the wood route and what happens when your ill,return from holiday to a cold house which will take days to heat up using a low powered heat source like wood.  Use a wood fire (enclosed and with a outside source of air) for evening/occasional use and to save on oil if you so wish.

Use a condensing oil boiler perhaps even a combi if there is a max of 2 showers.  This will have a capacity to do all your needs without worry and complication.

The balance between the oil and wood is then under your control depending on your circumstances.

I believe you are wrong to dismiss solar pv and hot water so readily as these are backed by government payments which means they pay for themselves.   The all black panels for example blend in well with most roof types. Solar pv will also reduce your expensive electricity bills as well as less oil.

But really it is investment in insulation that gives the best return not only by cutting total energy demand but using less expensive oil.  You may be well up in this area but not many really are.


Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: offthegridandy on August 25, 2013, 11:16:56 AM
Welcome Algy.

I have a system that works for me and you may wish to consider.

We have solid floors ground floors with UFH in 5 zones, the manifold for the UFH is principally supplied by an oil boiler.  We also have a smallish old Stanley wood stove with back boiler.  The wood stove output is pumped to a 200 litre direct Cu cylinder.  Cylinder has then got two take off's *, feed and return which link in to the UFH circuit adjacent to the manifold.  These 2 connections have motorised valves (MV)controlled by thermostat on tank. *Tank also has feed and expansion pipes I should add.

When main room stat calls for heat for the UFH the oil boiler will fire, but if wood burner is alight and Cu cylinder is hot (over 35') then MV's will open and UFH circuit will take hot water from cylinder and oil burner will not fire (relay stops firing signal). As long as wood burner is alight and cylinder is hot oil is not used, but in event that we are out and so is the fire then oil burner does job and floor (and house) is kept warm.  Note the low temp for valve operation 35' is because the UFH only circulates water in the 35' temp range.

The wood burner also does space heating in the open plan kitchen dining area, but with UFH you want the floor slab to be warm all the time due to the slow warm up time. I therefore deliberatley have a small wood burner otherwise we would have to have a massive fire burning to heat a large back boiler, this would also provide more space heat which would warm the rooms higher than room stats whilst burning more wood, in turn the UFH wood be "off", then when wood stove drops back the oil burner would be on longer to put heat back into the floor.

I hope this makes some sense to you, it does to me  but then its my system.


Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: brackwell on August 25, 2013, 11:46:45 AM

What do you do for hot water when the UFH has reduced the tank temp to 35C

Whilst it is a good system in that it allows a small heat source to store heat and then deliver a bigger "punch" when required but the downside are very significant heat losses in supply to the tank,storage losses and delivery losses when a wood fire burning more efficiently in the first place will deliver more heat for the same wood although not as well distributed as UFH


Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: todthedog on August 25, 2013, 11:47:36 AM
Welcome Algy

I don't know where you are but I would reconsider on solar water heating panels, ours have been fit and virtually forget, free hot water for 9 months of the year (Finistere) and would integrate easily with you oil fired boiler.

I too would go for a simple dry wood burner.  firmly of the view that simple is best.  In a similar situation inthat I don't think that I will want to be chopping too much wood in 10 years time.

Good luck

Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: offthegridandy on August 25, 2013, 12:15:52 PM
Hi Ken,

The oil burner is programmed to fire to supply domestic hot water to an indirect tank 3 times a day controlled by temp/stat. Oil burner is programmed to run on demand from 6 am to 10 pm for UFH circuit again only firing when room stat demands. But this firing is simply over-riden (stopped by relay) if wood burners buffer tank can supply UFH circuit.  Since installing this set up around 4 years ago we have reduced our heating oil consumption by just over 50% PA. With the ever rising cost of oil we win every time.

The system is simple and inexpensive, cost in addition to stove (SH) was direct CU cylinder, 2 MV's, standard tank stat and a few meters of 22 mm pipe I'd guess about 350. In the event that fire is out or tank is cold, oil burner does its thing by default.  In the event that a relay should fail oil burner again will do its thing, so house always stays warm.

The (well insulated) whole house is kept at minimum 18'C all winter long. The distance from wood burner to buffer tank is about 3 meters so heat losses are minimal and in any event are "in the room" so aren't really lost. To heat the whole house by wood burner wood require a much larger stove and buffer tank plus require someone to keep stove alight all day. This system suits us (inc 90 year old resident) as either way oil or wood works automatically.

I am currently considering making some solar panels to feed into the system to further reduce oil consumption.

Oh sorry Algy this isn't about me.


Title: Re: Just a Wood Burner or a boiler Wood Burner - ready to give up, advice please.
Post by: Algy on August 25, 2013, 03:42:47 PM
Thank you to all for your advice. I've decided to go for a straight forward dry wood burner and separate oil condensing boiler. There are so many decisions to sort out in rebuilding this house, I need to simplify some things. It will mean the wood burner will run a bit cleaner and the work needed as we put on years will be manageable.

I will rethink the idea of solar for water heating since that is not as much capital outlay as solar for electricity and could fit into a smaller roof area at the side of the house, but even then I wonder if the capital payback for just hot water will be worth it, but that's another question.