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

[johndow]

Hi

I have a wood burrner which has a back boiler that delivers hot water. There is one radiator off the cylinder, more as a vent , which gets toasty.
I have two questions to ask if anyone can help.....what effect would there be in adding another radiator, feeding from the first one, to another room, and, is it possible to run a radiator from the hot water feed to my bathroom? ( directly from the water pipe ) This would save a fair amount of work and expense!
We do have to run the hot water tap to release hot water even with the rad.

Thanks in anticipation.

John

 

[Flyfisher]

I'm not a plumbing expert but I can't see any particular problem with running another radiator off your back boiler. However, I don't think it's possible to run a radiator directly off the feed to your bathroom hot water tap because there wouldn't be any flow of hot water through the radiator except when the tap is actually on, which is hardly ideal. Unless I've misunderstood your intention.

The fact that you're having to run off hot water suggests that you don't have enough radiators to disperse the heat from the back boiler (an issue with back boilers because you can't easliy turn off the heat source as with gas or oil), so adding another one (or more) certainly sounds like a good idea and will save wasting all that lovely hot water down the drain.

You'll probably find that the wood burner/back boiler manufacturer can provide a lot of useful information in this regard. I believe you also have to consider the siting of radiators with back boilers because it's important that one, or more, of them will still work properly even in the event of a power cut, i.e. the pump stops actively circulating the water to all the radiators but one or two of them will still function correctly through convection only. This is important to avoid the water in the back boiler overheating.

The kW rating of your back boiler is a good starting point for working out how many radiators it could serve. Room sizes and insulation efficiency of the house will also play a part if you want to maximise the heat distribution around the house.

 

[Lime]

The "heat bleed" radiator can be extended if you wish.
It will almost certainly mean that the hot water is not heated so quickly though.

As for running a radiator off your hot water supply to your bath it would be possible but with several reservations and stipulations.
You would need a radiator that did not corrode easily otherwise the water would get contaminated and dirty.
A copper radiator would be fine.
If you wish to run the radiator off the flow to the bath, i.e. the hot water goes through the radiator before going into the bath, I suspect there are regulations that say you shouldn't do it, but it would work for the period the bath was running.
If you wish to have the radiator taking heat directly from the hot tank all the time you need to consider the gravity feed requirements and also fit a return pipe back to the tank cold supply at the bottom.
Very unconventional I might add.

 

[johndow]

Thanks for the advice, at the moment there is no pump. The water goes up from the back boiler
into the cylinder then to the rad which is only a few feet away in the upstairs bedroom.
I hadn't thought of a pump, this will help if I add another rad to the system much further away from the
cylinder.
I know nothing about pumps........here we go again!

Thanks again

John

 

[Cloudscape]

I have wondered if purged hot water (sometimes very hot) from such systems could be diverted through a radiator that was not on the central heating system, by temporarily opening a gate valve or two. This would be a bit of a Heath-Robinson arrangement, and there are probably byelaws to prohibit it?

 

[caliwag]

Err...sorry to worry you wood guys, but it had to happen. Paul in Canada has been warning us for some time. :mrgreen:

 

[caliwag]

Of course omitted to add link...

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=3526&page=1#Item_0

 

[johndow]

Oh well, that's it then. No more wood burning stove, no need then for an extra rad, no need to take up space in the garden to season the wood that burns cleanly without smoke etc etc..
It's back to the grid and a letter to the Scottish Gov to keep Hunterston, Torness et al going so that we get clean leckie.
Hold on though......I can't afford to heat the cottage using leckie, and I can't begin to argue for and against woodburning Vs leckie. It would take too long.
So back to the question.....all contributions are welcome and noted.

Thanks

John

 

[caliwag]

probably the wrong forum...try http://www.ebuild.com

 

[caliwag]

or maybe http://www.ebuild.co.uk

 

[Cloudscape]

The manufacturers of most back-boiler devices specify what they believe their equipment is capable of. What's the make and model of your boiler? If there's no pump, then it's gravity driven (hot water rising, cooler water falling). You might be able to add another rad, but there might be limitations as to how far away it is from the first one (and therefore from the boiler). There might be implications to slowing down the circulation process.

 

[johndow]

Thanks Cloudscape

It's a Morso Squirrel stove and it is gravity only, I was hoping to simply add another rad. The h/w cylinder it feeds into is
small, due to space constraints, but because it's small I was thinking that the amount of water heated may be sufficient to
feed another rad. If required, would a pump fit into my system and would it assist the water to another rad?
At the moment this is no more than a thought / enquiry, which if doable I'll tackle in the summer. It seems a shame to be running away hot water when it could go to better use. Equally, if it meant two useless rads instead of one very good....I'll not bother.

John

 

[Flyfisher]

As described above, you need a gravity-fed radiator to be able to dissipate the back boiler heat and prevent the water boiling. The hot-water cylinder also acts as a 'radiator' by transferring some of the back boiler heat to the tank of domestic hot water (DHW) although, as you're finding out, once the DHW is up to temperature no further heat can be removed without running off hot water through the taps, which is rather a waste unless you really do bathe a lot!

It seems that your stove/boiler combination is providing more heat to the hot water than is being dissipated by the existing radiator and DHW. I think you're right to add another radiator, maybe more than one, but the further the radiators are from the boiler the more likely they are to need a pump to circulate the water effectively because convection alone (gravity) won't be sufficient. The manufacturer's data should specify things such as max horizontal runs etc.

Another alternative might be to simply replace the existing radiator with a much bigger one. This will certainly reduce the water overheating issue, although the bedroom might then get too hot and it does seem a shame not to distribute the heat more evenly around the house.

 

[Lime]

Adding a pump will complicate the system and could cause problems, I wouldn't use one.
As the wood stove is relatively small a gravity fed system is probably the best bet.
if the run of pipe to the extra radiator is long then increasing the diameter of the pipe will reduce resistance/drag to the gravity flow.

 

[Cloudscape]

You can identify the model of your stove here:

http://www.morsoe.com/us/Products/Stoves

You can download the manual here:

http://www.morsoe.com/us/Brochures_and_manuals/Download

That might help you find out what the manufacturer recommends, but as Flyfisher says, your stove seems to be producing more hot water than your current system needs. Mind you, that's a better situation than not producing enough hot water.

 

[Andrew Bodenham]

The set-up you describe is pretty primitive, and would benefit from the installation of a control system. The domestic hot water gets overheated, which is potentially dangerous as well as a waste of energy and water when you dump that hot water. Meanwhile you'd like the heat elsewhere in the house via more rads.

I'd look at fitting a simple system using a diverter valve, a cylinder thermostat, and a pump.
Initially the heated water would flow to the heating coil in the cylinder to heat your hot tap water. Once this had reached the required temp (say 55 degC) the thermostat would close and activate the divertor valve, redirecting all the flow round the radiator circuit. As hot watar was drawn from the taps and the tank temp reduced so the thermostat would open and divert the flow back to the tank coil to re-heat the cylinder. And so on. The overall result would be hot tap water at near constant temperature, radiators at a higher temperature, pump circulating the water so that all rads would run at more equal temp.

You should be aware that because the fire is an uncontrolled heat source you must build in suitable precautions against overheating or pressurisation ofthe circulating water - this is why your system has a 'heat bleed' radiator in the first place. Essentially the design must avoid a situation in which the stove is heating water which then has nowhere to go, ultimately boiling, venting, or worse, leading to pressurisation and subsequent explosion. If you're not confident about designing such a system then any competent heating engineer or plumber should be able to advise you. You would need to design for power / pump failure, so an element of gravity circulation would need to be retained.

 

[MdB]

Two temperature / pressure safety relief valves + tundish + pipe to outside installed to building regs requirements would sound like a very good (ie essential) idea too.

 

[Andrew Bodenham]

MdB,

That's the sort of thing I had in mind, though assuming that the system fills from a header tank in the loft it may well be (should be?) open vented back to there. In which case perhaps the worst case scenario is that the boiler vents over into the tank. Less than ideal anyway.

John, what happens now when the stove is running hard and getting the water too hot? Does it start boiling in the pipework? Venting out somewhere?

 

[Penners]

I certainly wouldn't run a rad off the domestic hot water flow to the bath. The only time it'll get up to a decent temperature is during the short time that you're running a bath. And, as others have said, you risk contamination of your bathwater due to galvanic action (unless the rad is the same material as the pipe).

As to whether you could extend the existing heat bleed system - it's difficult to say. It would be a bit of a 'suck it and see' situation. You would probably either (a) increase the recovery time of your domestic hot water system (which may or may not be a problem), and/or (b) reduce the temperature of the heat bleed water.

 

[johndow]

Hi Andrew /MdB

Thanks for all that. Yes there is a vent above the header tank ( in the loft space ) that the water escapes from when too hot.
It was seeing this last week that made me think of adding the additional rad. The system is safe at present and was insalled by a plumber.........I'm able to do most plumbing ( not the theory ) and your idea of a diverter valve ..looks interesting and doable, with more info and instruction!

Thanks again

John