wood burner extra rad.....warmer cottage.

[johndow]

Hi Penners

What I'd want to avoid is having another rad which halves the heat to the the existing....ending with two inefficient rads ( as I think you're suggesting )rather than one very efficient rad. As Cloudscape has suggested I'll get the spec and check it.
That's assuming that I continue with the gravity system. I like the idea by Andrew. A warmer cottage by any means ( with the stove a the heart of it ) would by a good idea!

John

 

[Penners]

Yes, Andrew's idea looks good. If your existing system is regularly venting hot water back into the header tank, though, that suggests that there is more waste heat than the existing bleed rad can cope with. So you might get away with adding a second one without 'robbing' too much from the existing one.

 

[Lime]

Personally i'm all for keeping the system simple.
What is not often realised by people who enlarge their simple heating systems is that there will be extra fuel consumption coupled with a drop in heat output from the actual fire.
-So the once very hot fire is cooler and eats fuel!

However if the vent pipe is discharging hot water into the header tank it is very important to ensure the tank can withstand hot water.
Many header tanks installed in the past have not been able to cope with hot water resulting in deformation and catastrophic leaks.

http://www.south-staffs-water.co.uk/downloads/Scalding_information_note_Jan08.pdf

 

[Flyfisher]

What I'd want to avoid is having another rad which halves the heat to the the existing....ending with two inefficient rads ( as I think you're suggesting )rather than one very efficient rad.

Adding another radiator doesn't necessarily mean ending up with two inefficient rads. In fact, the one you currently have is inefficient because it isn't able to dissipate all the heat from the back boiler, resulting in an overheating system that requires you to run off hot water.

Ideally, the system should be balanced such that the rated capacity of the back boiler is evenly distributed by an equivalent capacity of radiators.

I agree with Lime that the more heat you extract from the stove (via the back boiler) then the more fuel it will burn, but in this case it seems that you're already extracting more heat than you need and then flushing it down the drain as hot water to stop the system overheating. Adding additional radiators that can dissipate the same amount of heat that's currently going down the drain won't result in any more fuel being burned, but it will mean that all the resulting heat will remain within the house.

In short, adding one (or more) rads will make the system more efficient, not less.

 

[johndow]

Thanks Flyfisher

It all sounds good for my initial thought, which was to add an additional rad whilst keeping it as simple as poss ( for me ) to do.
My main concern you have addressed. So, with a little more research, I'll be adding this work to the list for summer.

If all of the contributers to this forum feel like doing more than giving advice and fancy a break on a wonderful Scottish Island...........you can all help with the list!!

Thanks to all

John

NB
We have red squirrels and red deer visitors to our garden.( fence needs mending, but the deer are fun ).................and a local hotel.............and.......a distillery within a mile.........Golden eagles.......... a healthy tool box..............

 

[Jon Maine]

The squirrel is 6kw. It is eminently controllable and one of the most economic to run wood burners on the market.

Firstly a few facts.

Yes keep it simple on gravity with another radiator on the primary feed from the back boiler not the hot water side.

You will not burn more fuel because you have more radiators, you will burn more fuel if you open up the air vents on the stove.

Be very careful about boiling into your attic tank, there have been at least two fatalities in recent years where one of these header tanks has split whilst full of boiling water causing fatalities.

Add another radiator or two and adjust the valves accordingly to get heat where you want it.

Keep all of your flow pipes with an uphill gradient no matter how small.

No need for a tundish on an open vented circuit, un-necessary only needed for pressurised systems

Not that it is applicable but if you say put a towel rail in line on the hot water it would not work well without a return pipe to the base of the cylinder and have to include a non ferrous radiator or it will stain as lime says.

You must maintain adequate heat leakage on gravity from the stove, you could however then add some pipework teeing of to a lower location incorporating a pump controlled either by a simple switch or a thermostat on the heat leak pipe so before it gets to the overheat temperature the pump kicks in and you heat another area of the house.

I cant do more than point you in the right direction but it is quite critical to get it right so you don't boil the header tank, I think a thermostat set to say 85 degrees kicking in a pump to lower rads would be the solution I would go for.

Good luck

 

[MdB]

No need for a tundish on an open vented circuit, un-necessary only needed for pressurised systems

As long as there are no check valves, isolation valves, stop cocks, radiator valves etc in at least one of the pipes that vents to air. If both sides of your loop get switched off, you turn your boiler into a bomb. Obvious I know but worth saying.

 

[Jon Maine]

No need for a tundish on an open vented circuit, un-necessary only needed for pressurised systems

As long as there are no check valves, isolation valves, stop cocks, radiator valves etc in at least one of the pipes that vents to air. If both sides of your loop get switched off, you turn your boiler into a bomb. Obvious I know but worth saying.

A vented system should have no restrictions on the gravity loop whatsoever and also should not be allowed to boil over into the header tank as this has proven to be fatal also.

 

[Lime]

I'd like to emphasise safety, as others have done, concerning a wood burner with a back boiler.

Nothing should impede, stop or control the gravity loop system whatsoever.
It is vital that any work done does not attempt to divert or restrict the gravity system from operating normally in an emergency.

It is not clear exactly what type of gravity system is fitted to the squirrel burner.
If it is a conventional indirect system (as I'd expect) it will have two tanks in the loft.
One to supply water to the boiler system another to feed the hot water supply.
Both tanks needs to be capapable of withstanding hot water and have proper support.
See second page of pdf link:
http://www.south-staffs-water.co.uk/downloads/Scalding_information_note_Jan08.pdf

Any addition to the system should ensure it does not interfere with normal gravity circulation.

 

[Penners]

We have red squirrels ..

The squirrel is 6kw. It is eminently controllable

I wish we had 6kW squirrels. It would cut my power bill no end.