Unvented Boiler Stove Enquiry

Martin440

I am looking for a stove with a boiler for use with a 1000 litre heat store. Any suggestions or pointers would be welcome.

The requirements are:

1. Total stove output around 20 - 30kW with approximately 2/3 to water
2. Having a cooling loop and suitable to be used with an unvented system
3. Can use external air intake, i.e. can be room-sealed for use in highly air-tight house
4. Ideally traditional stove look (i.e. wide rather than tall), but with straight lines and not fussy looking
5. Reasonable cost

Thanks you

Froststop

Martin440 wrote: »

I am looking for a stove with a boiler for use with a 1000 litre heat store. Any suggestions or pointers would be welcome.

The requirements are:

1. Total stove output around 20 - 30kW with approximately 2/3 to water
2. Having a cooling loop and suitable to be used with an unvented system

Can't connect a stove directly to an un-vented/sealed heating system! This is the idea I'm getting from your quote above, correct me if I'm picking it up wrong.

Stoves must be treated as a standard back boiler and must be open vented.

Martin440

I have come across some stoves with cooling coil which can be used with unvented systems, such as this one:

http://www.modernstoves.co.uk/wood-burning-stoves-with-back-boiler/woodburning-stove-4.html

The problem with this one is although it can be used with an unvented system, it cannot be room-sealed.

Froststop

Martin440 wrote: »

I have come across some stoves with cooling coil which can be used with unvented systems, such as this one:

http://www.modernstoves.co.uk/wood-burning-stoves-with-back-boiler/woodburning-stove-4.html

The problem with this one is although it can be used with an unvented system, it cannot be room-sealed.

It's only rated to 2 bar. It's not suitable. Should be rated to a minimum of 3 bar.
Your safety valve on the heating is 3 bar. The stove has to be rated at least the same or higher. If the seller advised you it can be used then he should be fired!! That would be like a time bomb on your heating!

Martin440

Good point, Froststop, but as I say that one isn't suitable anyway for other reasons.

I just wonder if anyone knows of another boiler stove (or fireplace boiler) which would suit? (and meet the right pressure requirements!)

Thanks
Martin

Froststop

Martin440 wrote: »

Good point, Froststop, but as I say that one isn't suitable anyway for other reasons.

I just wonder if anyone knows of another boiler stove (or fireplace boiler) which would suit? (and meet the right pressure requirements!)

Thanks
Martin

Not available.

shane0007

Froststop wrote: »

Not available.

I agree but that's not to say it can't be done. There are other options available to have the stove open vented & the rest unvented.

Martin440

Is there anyone else who might have some suggestions?

shane0007

Martin440 wrote: »

Is there anyone else who might have some suggestions?

The issue is you cannot have an uncontrollable heat source into a pressurised system, be it for heating or domestic hot water.
Pressure & heat are directly related & uncontrolled, they can lead to disaster.

You have options but experienced care & attention must be given.

Martin440

Thanks Shane. As I understand it, boilers suitable for unvented systems have a cooling coil which cools the stove down if it's in danger of overheating.

Froststop

shane0007 wrote: »

The issue is you cannot have an uncontrollable heat source into a pressurised system, be it for heating or domestic hot water.
Pressure & heat are directly related & uncontrolled, they can lead to disaster.

You have options but experienced care & attention must be given.

I fitted a heat genie a while back, have you seen that system Shane? I was a small worried about it but it worked a treat after. You would be dependant on the safety equipment that comes with it. I actually got them to change the standard temp safety valve for one set to a lower temp. If the safety valve fails a disaster could be on the cards. Which I made sure the home owner was aware of before fitting. I must admit, I'm not a fan of stoves or back boilers unless they can be piped by the book.

Froststop

Martin440 wrote: »

Thanks Shane. As I understand it, boilers suitable for unvented systems have a cooling coil which cools the stove down if it's in danger of overheating.

How does it operate? On the heat genie it lets in cold water and dumps hot water to drain.

shane0007

Froststop wrote: »

How does it operate? On the heat genie it lets in cold water and dumps hot water to drain.

I don't like them. I would never rely on a moving part for safety.
What happens if the pipe freezes? What happens if the valve sticks closed?
What happens if the temperature sensor fails?
Plus they do not meet the new solid fuel regs coming out, which require a minimum heat dissipation of 20 litres. The Firebird system has 24 litres & no moving parts for safety, just good ol' f & e tank with a osvp.

Froststop

shane0007 wrote: »

I don't like them. I would never rely on a moving part for safety.
What happens if the pipe freezes? What happens if the valve sticks closed?
What happens if the temperature sensor fails?
Plus they do not meet the new solid fuel regs coming out, which require a minimum heat dissipation of 20 litres. The Firebird system has 24 litres & no moving parts for safety, just good ol' f & e tank with a osvp.

I would feel the same, don't like anything which depends on moving parts.
I fitted that one for the guy because I know him and he wanted it as he bought it himself before talking to me. I tried to talk him out of it but he was like a child in a sweet shop. If I had my way it would be in there at all.

Dtp1979

Froststop wrote: »

How does it operate? On the heat genie it lets in cold water and dumps hot water to drain.

What if the water is turned off by the council due to some works being carried out?

Froststop

Dtp1979 wrote: »

What if the water is turned off by the council due to some works being carried out?

It's an open system on the stove side. I fitted a rad in the attic and in the hot press to try and use the heat generated from back-boiler. Seems to work so far.

Martin440

shane0007 wrote: »

I agree but that's not to say it can't be done. There are other options available to have the stove open vented & the rest unvented.

Shane, do you mean with a heat exchanger between the vented and unvented circuits? I've thought of that, but I understand a vented stove requires a vertical pipe going up from it, which wouldn't really suit the open plan space planned.

shane0007

The Firebird heat exchanger can be located in the attic with the f & e tank above it. Then a pressurised flow & return back down to the system/thermal store.

mundogas

Any opinions on feeding everything (stove/gas boiler/solar) back to a vented thermal storage tank such as the Gledhill Torrent GreenHeat or similar. Currently looking into such a system but unsure whether leaving a smaller stove with no back boiler and going unvented with the rest might be a better option. Or as mentioned above by Shane with firebird heat exchanger arrangement.

Froststop

Dtp1979 wrote: »

What if the water is turned off by the council due to some works being carried out?

Forgot to mention the mains is fed off a well. The main problem would be a power cut to the pumps.

shane0007

Froststop wrote: »

Forgot to mention the mains is fed off a well. The main problem would be a power cut to the pumps.

So where's the fail safe?
There are frequent power cuts when stoves would be lit, so it will overheat.

Froststop

shane0007 wrote: »

So where's the fail safe?
There are frequent power cuts when stoves would be lit, so it will overheat.

If there's a power cut all stoves will over heat if power is off long enough. It will heat the cylinder on gravity. I fitted a manual valve on a separate cold feed form the storage tank and one to drain, by opening the cold feed valve and the drain valve it dose the same as the system link system. It was not on the spec with the equipment and I spoke to system link who could not advise if there was a problem with power. They said to run off hot water but I put this in to give another option in such a situation. All tested after fitting.

shane0007

Froststop wrote: »

If there's a power cut all stoves will over heat if power is off long enough. It will heat the cylinder on gravity. I fitted a manual valve on a separate cold feed form the storage tank and one to drain, by opening the cold feed valve and the drain valve it dose the same as the system link system. It was not on the spec with the equipment and I spoke to system link who could not advise if there was a problem with power. They said to run off hot water but I put this in to give another option in such a situation. All tested after fitting.

But the stove was on all day, cylinder is hot already. Owners have gone out for the night & the baby sitter & her boyfriend just packed up the fire to heat the parish when there was a sudden power cut! How would they know that they have to open a manual valve when there is a power cut?

But hold on, the owner had previously noticed the 3 bar safety valve had been dripping. He called another guy in as you were away on your jollies. This other guy thinks "jaysus, I've never seen a system like this & I ain't draining it down", so he just screws in another 3 bar safety valve into the leaking one. Now it's needs 6 bar to open.

IMO, a fail safe must be a fool's fail safe, but that just my opinion.

Froststop

shane0007 wrote: »

But the stove was on all day, cylinder is hot already. Owners have gone out for the night & the baby sitter & her boyfriend just packed up the fire to heat the parish when there was a sudden power cut! How would they know that they have to open a manual valve when there is a power cut?

But hold on, the owner had previously noticed the 3 bar safety valve had been dripping. He called another guy in as you were away on your jollies. This other guy thinks "jaysus, I've never seen a system like this & I ain't draining it down", so he just screws in another 3 bar safety valve into the leaking one. Now it's needs 6 bar to open.

IMO, a fail safe must be a fool's fail safe, but that just my opinion.

As I mentioned before, if I had my way it would not be there. If any back boiler is in use when there is a power cut the same could apply, likewise if the owners where out. It would boil up the vent.

If a plumber fits a 3 bar safety valve onto the existing 3 bar safety valve why would it open at 6 bar? they both open at 3 Bar.

shane0007

Froststop wrote: »

If a plumber fits a 3 bar safety valve onto the existing 3 bar safety valve why would it open at 6 bar? they both open at 3 Bar.

I'm afraid not. It will take 3 bar to open the first valve. The energy used to open that one will have greatly reduced as they are in series. So it would take another 3 bar to open the second.

If the were both fitted on the same pipe & not one screwed into the other, they would open at the same time but the pressure would drop in double the speed to close them again.

Try set it up as an experiment in your garage with air & you will see.

Wearb

Froststop wrote: »

As I mentioned before, if I had my way it would not be there. If any back boiler is in use when there is a power cut the same could apply, likewise if the owners where out. It would boil up the vent.

If a plumber fits a 3 bar safety valve onto the existing 3 bar safety valve why would it open at 6 bar? they both open at 3 Bar.

I had this conversation here on Boards a while back and eventually got my head around it. And besides, someone had set it up in a workshop to test it. The result was 6 bar.

So here is how I understand it in my head.
The 3 bar is not an absolute figure, but the 3 bars refers to the difference on both sides of the PRV. Therefore (without being too pedantic about it) you have zero pressure on the outside and 3 bar on the inside, then it releases. If you have lets say 2 bars on the outside, then it will take 5 bars on the inside for it to vent.
So with the PVRs in series; lets say the first one lets out an eggcup full of steam into the space between the 2 PVRs and that this creates a pressure of 2 bars in that space, it will now take 5 bars on the first one before it releases the next time.

I hope that was not too complicated. It sounded simpler in my head before I started to put it into words.

shane0007

Wearb wrote: »

I had this conversation here on Boards a while back and eventually got my head around it. And besides, someone had set it up in a workshop to test it. The result was 6 bar.

So here is how I understand it in my head.
The 3 bar is not an absolute figure, but the 3 bars refers to the difference on both sides of the PRV. Therefore (without being too pedantic about it) you have zero pressure on the outside and 3 bar on the inside, then it releases. If you have lets say 2 bars on the outside, then it will take 5 bars on the inside for it to vent.
So with the PVRs in series; lets say the first one lets out an eggcup full of steam into the space between the 2 PVRs and that this creates a pressure of 2 bars in that space, it will now take 5 bars on the first one before it releases the next time.

I hope that was not too complicated. It sounded simpler in my head before I started to put it into words.

Correct

Froststop

Wearb wrote: »

I had this conversation here on Boards a while back and eventually got my head around it. And besides, someone had set it up in a workshop to test it. The result was 6 bar.

So here is how I understand it in my head.
The 3 bar is not an absolute figure, but the 3 bars refers to the difference on both sides of the PRV. Therefore (without being too pedantic about it) you have zero pressure on the outside and 3 bar on the inside, then it releases. If you have lets say 2 bars on the outside, then it will take 5 bars on the inside for it to vent.
So with the PVRs in series; lets say the first one lets out an eggcup full of steam into the space between the 2 PVRs and that this creates a pressure of 2 bars in that space, it will now take 5 bars on the first one before it releases the next time.

I hope that was not too complicated. It sounded simpler in my head before I started to put it into words.

The two bar in the space between both PRV's creates a back pressure on the spring of the first PRV.

Makes sense.

SystemLink

Hi Guys,

I’m an engineer with SystemLink, the company which produces the Heat Genie. I came across this thread and noticed some incorrect information posted with regards to the Heat Genie and how it works. Rather than repeat it all again here, we have already had a discussion of similar issues on the following thread if anybody would like to have a look

http://www.boards.ie/vbulletin/showthread.php?t=2057121571

Systemlink’s Heat Genie is fully compliant with any regs or standards available including the new Part J which has just been published. The Heat Genie has been independently verified and approved by HETAS and as far as we know is the only Irish solid fuel link-up product to be HETAS approved.