Heating Expert?
Discussion
I know that it is not allowed to connect a solid fuel boiler into a sealed heating system but is it OK to connect a SF boiler to the heating coil of an unvented HW tank?
I want to have mains pressure hot water, so intended to get a twin coil unvented tank, one coil for wood burning boiler and the other coil for LPG boiler. Both systems will be vented.
I want to have mains pressure hot water, so intended to get a twin coil unvented tank, one coil for wood burning boiler and the other coil for LPG boiler. Both systems will be vented.
Mr Pointy said:
If the tank is unvented & connected to the incoming mains where would the water expand to when it gets hot?
I guess if the pressure exceeds the mains pressure it can only expand into the cold feed unless a check valve needs to be fitted, or perhaps an accumulator of some kind needs to be fitted. This is why I posted, Im not sure whats out there to enable this to be possible. There are unvented tanks for sale so it must be possible to do this in some form.
In my understanding you should not mix uncontrolled heat sources and unvented systems as this could lead to a increased likly hood of failure. Failure is not pritty there are some nice mythbusters youtube clips if you want to see the outcome of that.
It sounds to me what you need is a thermal store.
It sounds to me what you need is a thermal store.
Simple answer is yes.
You can have a mains pressure cylinder with heating coils. However the heating coils have to be open vented, hence the water in the coil is only acting as an energy transfer medium - if it boils it can easily escape.
The cylinder itself has its own set of valves for expansion etc.
Ferg can give you more advice about the UK legalities
You can have a mains pressure cylinder with heating coils. However the heating coils have to be open vented, hence the water in the coil is only acting as an energy transfer medium - if it boils it can easily escape.
The cylinder itself has its own set of valves for expansion etc.
Ferg can give you more advice about the UK legalities
What I meant to say......
If you have a mains pressure cylinder with a heating coil, and the heating coil is heated from say a back boiler (very common in logburners in New Zealand), this coil circuit has to be open vented as there is a risk of boiling and explosion.
As the coil circuits are notoriously low pressure it makes a lot of sense to use them as an energy transfer system only, and have a mains pressure cylinder for a decent shower.
Useless fact for today. New Zealand has the highest percentage of households in the world with an electrically heated hot water cylinder.
If you have a mains pressure cylinder with a heating coil, and the heating coil is heated from say a back boiler (very common in logburners in New Zealand), this coil circuit has to be open vented as there is a risk of boiling and explosion.
As the coil circuits are notoriously low pressure it makes a lot of sense to use them as an energy transfer system only, and have a mains pressure cylinder for a decent shower.
Useless fact for today. New Zealand has the highest percentage of households in the world with an electrically heated hot water cylinder.
In europe, you can heat an unvented cylinder with an unvented coil fed from a woodburner quite happily, but it all needs to be designed to do so.
Stove must be pressure-tested to lots-of-psi, with a quench coil in the boiler dumping cold mains water to drain via the boiler, an expansion vessel with overtemp and overpressure relief valves, pump and either a UPS or gravity feed.
And probably some other stuff I forget.
In the UK, as far as building control are concerned, we're still in the dark ages.
All of the unvented firey stuff and associated safety devices would quite possibly make the average hetas engineer cry
Stove must be pressure-tested to lots-of-psi, with a quench coil in the boiler dumping cold mains water to drain via the boiler, an expansion vessel with overtemp and overpressure relief valves, pump and either a UPS or gravity feed.
And probably some other stuff I forget.
In the UK, as far as building control are concerned, we're still in the dark ages.
All of the unvented firey stuff and associated safety devices would quite possibly make the average hetas engineer cry
Thanks to everybody for their replies so far.
Ferg, I know this is your game, so the questions below are just for my own understanding.
So if I have a thermostat fitted to the tank controlling a motorised valve on the coil is this not enough to isolate the heat source? Or does the motorised valve become the weak link in that if it fails open the tank becomes a potential bomb? Is there no fail safe device that you know of that would isolate the flow to the coil in a potentially dangerous over-temp or over pressure situation? I'm guessing not or I think you would have told me already. Sorry for all the questions.
Caziques, what you describe is exactly what I'm trying to do, you had my hopes up when I read your first post, seems Ferg has dashed them
Andy43, thanks for the info. The wood burner I'm thinking of is pressure tested to 4 Bar but it isn't relevant here as the system will be vented, it's only the Hot water tank I was trying to make unvented. Are you saying that there are ways to do what I'm trying to do but at present doesn't satisfy the regs?
If it's not possible then I'll just have to vent everything and install a shower pump.
Thanks again all.
Ferg, I know this is your game, so the questions below are just for my own understanding.
So if I have a thermostat fitted to the tank controlling a motorised valve on the coil is this not enough to isolate the heat source? Or does the motorised valve become the weak link in that if it fails open the tank becomes a potential bomb? Is there no fail safe device that you know of that would isolate the flow to the coil in a potentially dangerous over-temp or over pressure situation? I'm guessing not or I think you would have told me already. Sorry for all the questions.
Caziques, what you describe is exactly what I'm trying to do, you had my hopes up when I read your first post, seems Ferg has dashed them
Andy43, thanks for the info. The wood burner I'm thinking of is pressure tested to 4 Bar but it isn't relevant here as the system will be vented, it's only the Hot water tank I was trying to make unvented. Are you saying that there are ways to do what I'm trying to do but at present doesn't satisfy the regs?
If it's not possible then I'll just have to vent everything and install a shower pump.
Thanks again all.
If you had a heat dump radiator tee'd into your presumably gravity fed boiler-to-coil system, and used a normally open valve on the rad, together with a normally closed valve to the coil, that would work.
Thermostat on boiler switches gravity flow to the coil when hot. If it gets TOO hot at the cylinder, an overtemp stat on the cylinder then breaks the circuit and everything failsafes to the heatdump. Same goes during a powercut - fail to heatdump. Whether hetas or BCO would be happy with that I have no idea to be honest.
If you can't gravity feed (at least to a heat dump), and have to pump, then it becomes very difficult if not impossible to work within UK regs. In Yerp, you can do it. Here, we're at least 30 years behind the times.
I'm not a professional btw, so have no clue whatsoever as to what meets Uk regs or not
Thermostat on boiler switches gravity flow to the coil when hot. If it gets TOO hot at the cylinder, an overtemp stat on the cylinder then breaks the circuit and everything failsafes to the heatdump. Same goes during a powercut - fail to heatdump. Whether hetas or BCO would be happy with that I have no idea to be honest.
If you can't gravity feed (at least to a heat dump), and have to pump, then it becomes very difficult if not impossible to work within UK regs. In Yerp, you can do it. Here, we're at least 30 years behind the times.
I'm not a professional btw, so have no clue whatsoever as to what meets Uk regs or not
eddie1980 said:
In my understanding you should not mix uncontrolled heat sources and unvented systems as this could lead to a increased likly hood of failure. Failure is not pritty there are some nice mythbusters youtube clips if you want to see the outcome of that.
It sounds to me what you need is a thermal store.
Thanks eddie1980, I'm in contact with a company who make thermal storesIt sounds to me what you need is a thermal store.
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