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Author Topic: Wood fired central heating, I'm a bit stumped!!  (Read 12079 times)
Markrt
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« on: October 30, 2008, 05:23:10 PM »

We have just had a central heating/hot water system installed running from a multi-fuel (mainly wood) stove, a Charnwood SLX45. it is running 8 radiators and the hot water through a thermal store and the whole system is brand new. Unfortunately it doesn't seem to be working very well. We are very new to this having renovated an old cottage (more insulation than you can shake a stick at - walls, floors, loft). The output of the stove is 9.2kw to water and 3.2kw to room but its like it isn't enough. It has a full control system wired in (which won't work) and two immersion elements for boost but even with the fire running all day the temperature inside the tank never seems to reach the level I was told to expect, the most it's got up to is 70C. I know these things take a bit of time to get used to but no matter what we do we A.) can't seem to get the hang of this or B.) have been sold a pup! We took extensive advice from the person that installed the system and made it very clear that we weren't at all knowledgable about this. The installer basically told us which route to take and assured us the system was up to the job. It isn't a big house but I have to say, at the moment, it's a bit of a cold one.
Does anybody out there have any advice for a complete novice? I feel like a bit of an idiot asking but having read through some of the posts on here it seems this could be a good place to start.
I should say that I would like to ask the person that installed it but  three qaurters of the way through the job he basically gave up, we had to get a different plumber in just to pressure test the heating system (all the rads were leaking).

Any advice for the village idiot would be so welcome!
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lightfoot
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« Reply #1 on: October 30, 2008, 06:03:55 PM »

Hi Markrt,

Can you tell us a bit more about the system, did you have a written design spec, ie what size/make is the thermal store, where is it in relation to the WBS, how is it all configured/connected up, how much DHW do you get through a day and do you have any idea what the peak space heating requirements are and/or the floor area of the house etc etc.....do you have any drawings or pictures ?


Cheers

Lightfoot.
« Last Edit: October 30, 2008, 06:05:34 PM by lightfoot » Logged

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dhaslam
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« Reply #2 on: October 30, 2008, 06:16:00 PM »

One point to note is that multi fuel stoves are normally rated for coal so timber can be as little as two thirds.    If you are running eight radiators then you are probably using a good bit more than the stove can produce.    Try reducing the number of radiators running.   The other thing to check is the flue temperature.   Make sure the flue is reaching 150 C or so.  Note that all heating systems need a lot of heat to get temperatures up but then good insulation should take over and ease the situation.  Unfortunately you may need to increase the size of your stove.   Charnwood do wood specific stoves which should output the full rating.   How is the temperature in the room where the stove is located?
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Markrt
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« Reply #3 on: October 31, 2008, 02:29:43 PM »

OK, I'll give as much info as I can. The thermal store is a 250litre Gledhill Torrent located in a bedroom cupboard on the first floor poking up into the loft through a hole cut into the ceiling, this has a Charnwood control system fitted, the stove is in the main living area on the ground. Distance is about 2.5 metres up and 3 metres across (if that makes sense!?). We use a relatively small amount of hot water, about two baths full, and that is mainly used early evening after the stove has been running for at least ten hours (the tank temperature has never gone beyond about 70 even after that amount of time). The system does provide a decent amount of DHW but no heat to the rads, when it does put something into the heating it's for about ten minutes and then stops feeding them. Most of those that are on get quite warm to the touch but then the feed stops and they cool down, it's never long enough to produce any sustainable heat despite the house being very well insulated. I have turned off two of the rads (and a very small one in a loo just doesn't work, almost like it isn't connected at all) in an attempt to get heat to the others but it has made no improvement. There is a new extension (built to modern regs with a little extra insulation for good measure) that has a utility room (1 rad) and a bedroom above (1 rad), neither of these  get any kind of useable heat at all, they feel slightly warm to the touch but that is it. As it stands we have 5 rads open and asking for a supply but it's not happening. The configuration seems to be a fairly standard approach, from what I've seen and what I've tried to find out, a pumped CH sytem with gravity fed heat loss rad.
I'm afraid I can't give you floor areas off the top of my head but it's a fairly small house. An open plan living/dining area and kitchen, one rad in the kitchen one in the dining area and the stove (dining area rad is off but could do with being on!). There's the new built bit (ute room, 1 rad and loo with a tiny rad that doesn't work), upstairs there's the bedroom in this bit (1 rad), the landing (1 rad that's off), a middle bedroom with the heat loss rad (usually lovely and warm!), another bedroom (1 rad) and the bathroom (1 rad). It is a 3 bed house but it isn't as big as anything built in the 50's, 60's or 70's, it's more the size of a modern Barratt Box. It's fully double glazed and the insulation really is up to scratch so if we did get some useable heat it would be retained.
We didn't get a written design spec but the 'installer' guided us through, made the calculations for space and DHW heating and said it would be plenty. It doesn't seem to be. The room where the stove is is quite cold too but this would be better if the rad worked.
The stove itself doesn't seem to be functioning as it should do either, we can't get a real blaze going, there doesn't seem to be a good 'draw' even though it has it's own vent about 150mm in front of it and the glass blackens up very quickly because it isn't burning hot enough. The chimney was relined but the stove was really just thrown in (the access point for sweeping is on the wrong way and faces the rear of the fireplace so can't actually be used) so may not be set properly, if that is a posibilty?
I hope this gives you some idea because I have none. A bit of advice on what to try or next steps would be great.
Thanks for taking the time.
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dhaslam
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« Reply #4 on: October 31, 2008, 02:53:24 PM »

It looks like the air intake to the stove is inadequate.   There is a air inlet bypass which needs to be opened, this will bypass the thermostat which may be closing too early.    The return water to the stove may be too cool as well, particularly if the control system isn't running properly.  This has the effect of cooling the flue gases and preventing secondary burning.    Chopping timber into small sizes will help increase temperature by increasing the surface area.       
 
http://www.charnwood.com/pdfs/Instructions/SLX45.pdf
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Markrt
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« Reply #5 on: October 31, 2008, 03:50:51 PM »

I did think about the bypass and will certainly give that a go. I can also reduce the log size. The other stuff I had no idea about, thanks for that.
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lightfoot
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« Reply #6 on: October 31, 2008, 04:05:47 PM »

Roughly how tall is the chimney above the WBS ?

Is the primary circuit from the WBS to the thermal store pumped or gravity only and what size is the pipework ?

Do you know whether the primary circuit is connected directly or via a coil (indirectly) ?

Are the rads fed via the thermal store or direct from the WBS/tee'd off the primary flow and return ?

I assume you are burning well seasoned logs ?

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Mother Nature is a wonderful housekeeper - but eat her out of house and home and you may just get your marching orders.
davec
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« Reply #7 on: October 31, 2008, 04:26:29 PM »

I've just fitted a very similar Charnwood stove, the LA45iB, running 8 rads, towel rail and 175l DHW cylinder. DHW is fed by gravity and rads are pumped from the boiler (so maybe this is different from your thermal store arrangement) according to a control system wired like the Charnwood-branded one... this has one pipestat that keeps the pump off until the boiler return hits 45deg, to prevent condensation, and another that unconditionally switches on to dump heat and prevent boiling if the gravity feed goes over 85deg; there's also a timer and a roomstat.

I note you're disappointed the store never goes past 70deg... the stove has its own automatic air control that's driven by the boiler temp... mine seems to shut itself down about 65deg, even when the manual control is set high.

I had some teething trouble with the control system - basically the sparkie who installed it didn't understand the logic and wired the low-limit stat back to front so it ran the pump up to 45deg then disabled it... smoky glass was the result and the rads only came on when the high-limit stat hit 85deg (i.e. pretty much never because of the stove's air control). I'm not saying that yours will be the same cause but you see what one wiring error can do... Could you elaborate on how yours "won't work"?

For the boolean minded, the logic is PUMP_ON = high_limit OR (timer AND roomstat AND low_limit)

The stove should do the job for you . I'd say there's a control system problem - Get the installer back. (the Charnwood control document gives a simple test procedure that may give you some clues)
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Markrt
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« Reply #8 on: October 31, 2008, 05:29:26 PM »

Wow, masses of stuff to think about! Lightfoot, I'll get those details. Davec, those symptoms are all too familiar. Dhaslam, I'm going to look at the bypass in the morning when the stove is a bit cooler.
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Markrt
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« Reply #9 on: November 05, 2008, 01:04:11 PM »

Thanks to you all for taking the time on this. The situation has changed a bit. We had a leak on one of the main boiler pipes (which is all 28mm to the store by the way) and had to get a plumber in to sort that out (the original installer doesn't want to know but that's a different story). The plumber had a bit of a look over the system and we went through some stuff that got it going ok and (fingers crossed) has done the trick.
I think I'm going to get myself on a plumbing course so I can at least try to grasp the basics of this. Any offers on a good place to start?
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Brandon
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« Reply #10 on: November 05, 2008, 07:46:32 PM »

Any offers on a good place to start?

I send my apprentices to yale in wrexham.
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« Reply #11 on: November 20, 2008, 04:54:07 PM »

Any offers on a good place to start?

I send my apprentices to yale in wrexham.

     Bloody hell
                       I went to skool at yale in wrexham !!
              Dave
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