Woodburner problems

[New Forest DEAN]

Hi All

 

Not sure if this is the right section to ask.....

 

I've just had a Clearview 650 stove with the wraparound back boiler (the biggest for that range at 40,000 BTU) serving a thermal heat store and then onto radiators - no other heat source (no gas or oil) apart from solar hot water.

 

I know the best operating temp for the wood burners is 250 - 350, but I can't get it even close. Stacked up and flat out with good seasoned wood it only sits at 150 degrees C, which is a poor burn.

 

I suspect this is because the boiler is sucking so much heat off (although the tank doesn't seem to heat up very well either!).

 

Anyone else had similar problems? you guys seem to know a lot about burning stuff

 

Any advice welcomed.

 

Cheers - DEAN.

[Martin Jenkins]

I have a Dunsley Highlander 10CH - smaller than yours. I do get a good amount of heat out of it, but have not used a thermometer. It is our only heat source like you, with solar hot water not doing an AWFUL lot this summer!

 

It does have a sweet spot.

 

What I am told, is that the optimal temperature for burning will really only be hit when the wraparound back boiler is actually hot. Otherwise the fire is always struggling with heating up the boiler.

 

In order to make this happen, a load valve is required, that joins the flow and return, so when the water is cold to start with, then it does not take very long to heat up just the water in the boiler; once it is up to temperature, it will let hot water through to the thermal store.

 

I have bought one, but not yet got it fitted.

 

You might already have one though!

 

You can tell if this is a real issue by waiting until the whole system is hot, and then seeing if that makes any difference to the temp.

 

The other possibility is the draw. Adding an external air supply to the Dunsley made a pretty big difference; although my bro-in-law is going to go further and use a double lined flue for his air supply, and thereby get pre-warmed air.

[Woodworks]

Hi Dean

I suspect your right about the boiler keeping the firebox temperature down it is common complaint I hear from people with back boilers on stoves that without burn very well. I am probably teaching my grandmother to suck eggs but make sure you are burning well seasoned wood. Cut a log in half and test the moisture content, this should be ideally be between 20-25% even lower is even better. I know some people who have put fire bricks in inside the stove to stop the back boiler drawing all the heat away. The Clearview OMHO is a very good choice of stove

[New Forest DEAN]

Cheers Guys

 

I've been looking at a LADDOMAT heat charger, which does what you said - puts the water into a loop near the boiler until it reaches 72 deg C before it goes up to the tank, thus keeping the boiler up to temp. Not sure if they are any good though?

 

Clearview have recommended that I do a test with 'heat logs' (sawdust logs?) - I was going to try a bit of coal anyway.

 

Lastly, its possible that the plumbers have put too much horizontal pipework on the gravity feed to the tank (80% horiz / 20% vert - should be the other way round).

 

Incidentally, I have read on a website that two small woodburners (without boilers) are often better and more efficient than one large burner / boiler. Good in theory, but no hot water.....

 

Thanks again - DEAN.

[Alycidon]

The problem you have is with the plumbing not the stove.

 

What is happening is that the stove is getting all the cold water back into it thereby reducing the stove heat. You will also be getting tars and excess soot in the flue due to the low firebox temperatures.

 

Talk to your plumber, Esse do a Boiler Control unit, this is an external box that will not allow cold water to flow back into the stove untill the stove ( or cooker) has reached its operating temperature, it then maintains that temperature by regulating the return ( cold )flow back into the stove. I think this the same or a similar bit of kit that Martin Jenkins is talking about. I am sure that there are other similar devices on the market.

 

As an aside I assume someone has signed the installation off as safe to use?.

 

A

[Martin Jenkins]

I tried the laddomat, but sent it back because it was not really good for my situation.

 

I have a buffer tank almost directly above my stove, and the laddomat (about £400) comes with a pump, driven off a thermostat, and it basically did not work, and the pump was too loud for the room it is in (which is my office!).

 

So I got rid of that and got a non-pumped ESBE load valve (about £100) which is just the valve, and it will use gravity to move the water around.

[Martin Jenkins]

...as I said though, to be sure that your immediate problem is to do with the temperature of the water in the boiler, run the system until the water is hot, then see how it performs.

 

If it is STILL not performing, look elsewhere (as well).

 

The recommendation is still to get a load valve (or charger, whatever it is called), but worth knowing what the actual issue is.

[Fisherman]

All our heating and hot water comes from wood during the winter and we have a laddomat between the boiler and the thermal store. Once the boiler is up to temp it slowly releases heat to the thermal store without droping the temp in the boiler, giving a good clean burn. Our 80Kw boiler takes about 6 hours to heat up the 4000 litre thermal store and services 28 radiators and 7 bathrooms. Works a treat with the laddomat.

[Marko]

Sustainable heating using wood fuel at Coed Cae B&B, North Wales is a good read to sorting similar problems (but with a wood boiler.

[hardtop110]

I've got a laddomat on our setup - it helps a lot in getting the whole lot up to temperature. The effectiveness depends on distance to the tank too, as there are limits - 6m of pipe work sounds familiar. You can change the stats in them too

 

Edit - Esse do a slightly cheaper copy of them.

Edited September 3, 2012 by hardtop110
additions