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  1. #1
    Member Rank = Nisai Smiffy's Avatar
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    Gas Boiler Specification

    Hi All,

    I have just finished my new Koi pond and introduced my 6 faithful fish to it. Thanks to everyone on the forum that helped me along the way - the advice has been invaluable and I think I have created a pretty nice pond with a good specification for keeping healthy Koi.

    The original fish have finally been moved from my original 1200L pre-formed pond to their new 11,700L pond and I have to confess that it's well overdue. The original 6 fish are of mixed herd breeding and cost me £25 for 10 of them around 8 years ago from a garden centre so worthless so far as breeding etc. is concerned and given their age are not particularly large compared to Japanese fish. They are however, very hardy as they have never been heated and the old 2 foot pond dropped to near zero over the winter months.

    Anyway, my plan is to introduce some new "proper" Koi in the future and thus during my pond build I have included a 100,000 BTU heat exchange unit as per below...
    https://www.absolute-koi.com/heat-exchangers-120/

    This size is rated for ponds up to 7500 gallons whereas mine comes in at around 12,000L (including filter etc.) which is circa 2640 gallons, so around 3 times over rated which is hopefully the way to go.

    However, I have no idea how to specify a gas boiler or how it is connected to the heat exchange unit. I have spoken to a CORGY gas fitter but he has never done a boiler for a pond before. I have no intention of doing it myself but need to create some kind of brief to give to a gas installer so as to get a quotation for the boiler and works. I have already run the yellow gas pipe to my filter house where the boiler is to be installed and running water is available. I assume I need a pond thermostat instead of a normal room thermostat similar to this?... https://www.absolute-koi.com/pro-dig...-m-probe-1903/

    Given that a reasonable size central heated radiator comes in at around 5000 BTU's a rating of 100,000 BTU's for the H.E. makes no sense to me at all and sounds way off the chart but I assume BTU's for water and air are two different things?

    Anyway, apologies for the lengthy post and any help much appreciated.

    Andy



  2. #2
    Extreme Koi Member Rank = Kyusai NickK-UK's Avatar
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    A 28kW boiler converted into BTUs is ~95,500 but/hour. So that's close to your 100Kbtu/hr.

    Given our 3 bed end of terrace was quoted as needing a 28kW combi although we increased that to 32kW for the increased hot water through put for the planned rain shower.

    BTUs should be the same for air and water, however water conducts heat but also presents a easier way for the walls, air above and floor to conduct the heat away from the pond.

    I think the first question you need to answer is what is the need - ie the amount of kWh or BTUs you need to heat the pond to maintain X degC in YdegC outside temps (assuming insulating cover is on over winter).
    1700 litres on 50 watts
    Eco Pond 2.0: 13,000 litres, 58W airlifts, 1300l anoxic, Solum 16. No pump.

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  4. #3
    Member Rank = Nisai Smiffy's Avatar
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    Hi Nick,

    Thanks for your comments. So the heat exchange enables rapid transfer of the boiler hot water to the pond water due to the high flow rate of pond water and the fact that it is conducted heat and not radiated which makes sense.

    I should have mentioned that the pond has 15mm Kingspan insulation including the floor but it also has two windows but I might cover one of them for winter. I have yet to make/buy covers but that would be my intention.

    Given that the BTU rating of my H.E. is almost 3 times over rated would it be safe to assume that the 28kW boiler would be suffice? Would the H.E. be connected just like a single radiator circuit? Is there anything else to consider? For instance if the pond circulation pump failed?

  5. #4
    Member Rank = Sansai Point's Avatar
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    Is your gas boiler just going to serve the pond or are you looking to connect the heat exchanger to your house heating system?

  6. #5
    Member Rank = Nisai Smiffy's Avatar
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    Hi Point,

    It will be dedicated to just the pond.

  7. #6
    Member Rank = Sansai Point's Avatar
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    You will need to work out the heat loss from your pond in order to size the boiler. If the pond isn't covered it is very difficult to calculate as evaporation losses come into play, along with numerous other factors. If you have a pond cover in the winter it is pretty easy to work out.

    If you look at the DTF's new pond thread here, from page 33 onwards, I've explained how you calculate the heat loss for a covered pond. https://www.koiforum.uk/pond-constru...s-pond-33.html

    I'm struggling to see how the manufacturers can say that a certain size is suitable for a specified pond volume.. without knowing the parameters they used to calculate it is meaningless. Your heater will be more than big enough for your pond as it is oversized, but it would be costly to just match a boiler with the same capacity. You won't need 29kW of heating.

    As for connecting the boiler to the heat exchanger, it is the same as a radiator system in your house. Don't get a combi boiler, just get a system boiler which will include an expansion vessel and primary circuit pump (the heating circuit) within the unit. Then you just run pipework between the boiler connections and the heat exchanger, include a thermostat like the one you posted, and you're set. The boiler will come with instructions for the installation requirements which any competent plumber should be able to follow. Oh, and don't forget to insulate the pipework.

    Having said that you may want to consider something... The UK is moving away from gas as a fuel.. in 2025 it is planned that gas boilers will no longer be allowed to be installed in new build properties. It has not been passed as Regulation yet but it is virtually guaranteed. It isn't known whether boilers that need replacing after that will be allowed to be gas or not but my feeling is that they'd need to be replaced with electric boilers, or domestic hydrogen boilers (which do not currently exist).

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  9. #7
    Senior Member Rank = Rokusai Simon Fish's Avatar
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    Hydrogen boilers are already in existence "Hy Grove"

    How did you size the gas pipe run so that the pressure loss would not be more than what's allowed?

    'Insulate Britain' is a currently hot topic, 15mm of insulation is that typo?
    The planning needs to be invested in conserving the heat.

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    Member Rank = Sansai Point's Avatar
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    As far as I'm aware the Worcester hydrogen boilers are still prototypes which are being tested in one or two developments. Hydrogen boilers are not available to purchase yet (to the domestic market) but I'm sure they will be by 2025. It is a race at the moment to see who can get a domestic hydrogen boiler tested and on the market.

    The thing with hydrogen is that there are various grades of it, produced using different fuels and/or processes. The two most suitable are blue and green hydrogen. Blue is cheap but uses gas to produce it, and hence produces CO2, whereas green uses electricity and is clean, but costs 2-3 times as much. You can't put both down the same network pipe at the same time so I wonder which one will they be using... cheap and dirty or expensive and clean?

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  13. #9
    Member Rank = Nisai Smiffy's Avatar
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    Quote Originally Posted by Point View Post
    You will need to work out the heat loss from your pond in order to size the boiler. If the pond isn't covered it is very difficult to calculate as evaporation losses come into play, along with numerous other factors. If you have a pond cover in the winter it is pretty easy to work out.

    If you look at the DTF's new pond thread here, from page 33 onwards, I've explained how you calculate the heat loss for a covered pond. https://www.koiforum.uk/pond-constru...s-pond-33.html

    I'm struggling to see how the manufacturers can say that a certain size is suitable for a specified pond volume.. without knowing the parameters they used to calculate it is meaningless. Your heater will be more than big enough for your pond as it is oversized, but it would be costly to just match a boiler with the same capacity. You won't need 29kW of heating.

    As for connecting the boiler to the heat exchanger, it is the same as a radiator system in your house. Don't get a combi boiler, just get a system boiler which will include an expansion vessel and primary circuit pump (the heating circuit) within the unit. Then you just run pipework between the boiler connections and the heat exchanger, include a thermostat like the one you posted, and you're set. The boiler will come with instructions for the installation requirements which any competent plumber should be able to follow. Oh, and don't forget to insulate the pipework.

    Having said that you may want to consider something... The UK is moving away from gas as a fuel.. in 2025 it is planned that gas boilers will no longer be allowed to be installed in new build properties. It has not been passed as Regulation yet but it is virtually guaranteed. It isn't known whether boilers that need replacing after that will be allowed to be gas or not but my feeling is that they'd need to be replaced with electric boilers, or domestic hydrogen boilers (which do not currently exist).

    Thanks for pointing me DTF's thread and for the installation comments etc. which are super useful.

    It all looks a bit complicated at a glance but I will go over it again. I'm not sure where you get all of the loss factors from for different materials/thicknesses/gaps etc.

    I have already installed the H.E. into my pond return pipework so changing over now would be a pain in the arse not to mention a waste of £200 + pipes + time... However, it could be an expensive mistake to continue on the wrong path. From my perspective, 95% or more of domestic/industrial properties in the UK have gas fired heating/water, not to mention the number of gas ovens and hobs so gas will be around for the foreseeable future. It is estimated to cost £26k on average to switch from natural gas to hydrogen so it's a monumental government ambition.

    The switch from natural gas to hydrogen is not likely to happen in the next 10 years and dual fuel boilers are not widely available and no doubt cost prohibitive at this point.
    That said gas prices are soaring but may still be cheaper that an electric ASHP?

    Anyway, I will attempt to calculate the pond heat loss etc.. I will be adding covers but do not yet have any as the pond was only filled 10 days ago but I can borrow the values from DTF.

    Cheers

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    Member Rank = Nisai Smiffy's Avatar
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    Quote Originally Posted by Simon Fish View Post
    Hydrogen boilers are already in existence "Hy Grove"

    How did you size the gas pipe run so that the pressure loss would not be more than what's allowed?

    'Insulate Britain' is a currently hot topic, 15mm of insulation is that typo?
    The planning needs to be invested in conserving the heat.
    Hi Simon,

    I'm assuming that hydrogen boilers would have run on natural gas for the next 10 years or so or until the supply is switched over? If that is the case I would probably be better off getting one in 10 years when the technology is well established and prices have dropped.

    I can't lie, I spoke to the builder and he said that 20mm would be ample - but I appreciate he was a builder and not a gas fitter and knows nothing about the spec in reality. There are no elbows or connectors but it is a pretty long run of around 25-30m, have I messed up?

    Most of the videos I saw on fibreglassing used 12mm insulation (Matt from GRP Lining Services mostly) so I thought 15mm was on the generous side? Going 50mm detracts massively from the water volume and I assumed most heat loss would be from the water surface and windows.

    So far as conserving heat goes, I could cover one of the windows with thick insulation, say 100mm and put covers on, yet to be sourced. The pond is protected by bushes on one side and the filter house on another.

    Cheers

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  17. #11
    Member Rank = Sansai Point's Avatar
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    Quote Originally Posted by Smiffy View Post
    Thanks for pointing me DTF's thread and for the installation comments etc. which are super useful.

    It all looks a bit complicated at a glance but I will go over it again. I'm not sure where you get all of the loss factors from for different materials/thicknesses/gaps etc.

    I have already installed the H.E. into my pond return pipework so changing over now would be a pain in the arse not to mention a waste of £200 + pipes + time... However, it could be an expensive mistake to continue on the wrong path. From my perspective, 95% or more of domestic/industrial properties in the UK have gas fired heating/water, not to mention the number of gas ovens and hobs so gas will be around for the foreseeable future. It is estimated to cost £26k on average to switch from natural gas to hydrogen so it's a monumental government ambition.

    The switch from natural gas to hydrogen is not likely to happen in the next 10 years and dual fuel boilers are not widely available and no doubt cost prohibitive at this point.
    That said gas prices are soaring but may still be cheaper that an electric ASHP?

    Anyway, I will attempt to calculate the pond heat loss etc.. I will be adding covers but do not yet have any as the pond was only filled 10 days ago but I can borrow the values from DTF.Cheers
    As part of the Future Homes initiative, which will be implemented to meet zero nett carbon emissions by 2050, the Regulation will be, as it is proposed now, that all new build homes will not be allowed to have gas fired boilers installed. Yes, it is a monumental ambition but, barring any backpedalling, this is what is going to happen. I'm currently designing the mechanical services for various house types for future social housing developments and the industry is already planning for the changes that are coming.

    If a house already has a gas fired boiler and it fails after 2025 it is unknown at the moment what will be allowed to replace it. Both hydrogen and electric boilers should pretty much be a straight swap over.. once infrastructure is in place. Because of this simple swap over I'm not saying you using a boiler for pond heating is folly, but it does seem an expensive way to do it imho. It would be cheaper to take a circuit from your house heating system to the heat exchanger if you can.

    If electric boilers or ASHP are taken up en masse in 2025 to meet residential heating needs there will be a lot of benefit from installing pv panels to offset the electricity cost. They could also be useful to help with pond heating systems.

    As in the DTF thread, heat loss through anything is thermal conductivity (U value) x area x temperature difference. U values can be complicated to work out for people who don't have the base data of the materials.. luckily for you I do this for a living so if you can tell me what your pond construction is and the thickness of each of the materials I can work the U values out for you easily. If you are going to make a pond cover I'd strongly suggest that it is double layered with an air gap inbetween.

    With regards to the gas pipework that Simon mentioned; gas installations are subject to strict Regulations. Pipes need to be sized correctly, run at the correct depths externally, at certain distances from other services, and marker tape laid over them, and connections at the ends need to be done right. It's not simply a case of connecting yellow mdpe to your boiler, or the meter. Yellow mdpe is not UV stabilised so none of it should be open to daylight.

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  19. #12
    Member Rank = Nisai Smiffy's Avatar
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    As you are clearly an industry expert I fully accept and acknowledge your points, Point

    Given that my need is relatively urgent if I am to go down the gas route then I will be happy to swap over to hydrogen as and when in the future.

    Running pipes from the house is technically feasible but would create a lot of disruption. I will however, explore this route further as the pipes could be laid under my patio which is only on dry mix and is due to be replaced next year anyway. My house is only 4 years old and the central heating is run with 10mm plastic pipe rubbish - would this be suffice for the heat exchange given that it has 1" threads on it? Can the H.E. be included in the existing rad circuit? This would be much easier as I can get to an external wall with a rad on the inside.

    If I went the ASHP route I guess I would need to bring a new circuit from the house consumer unit? Currently my filter house power is a radial from the downstairs power ring via a 2.5mm armoured cable. I appreciate that this is dependant upon the rating required.

    I did the research on the mdpe gas pipe and it has been cemented into a new wall footing at 400mm+ and the yellow warning tape was placed on the footing before it was filled. I also used the metal risers to bring them above ground.

    Very kind of you to offer to do the calculations, I will put together the details over the weekend.

    Thanks again

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    Member Rank = Sansai Point's Avatar
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    Whoa, steady on.. no experts here lol, but I have been a services design engineer for over 35 years so I've picked up a couple of things.

    The plastic pipe used in your house is suitable for heating so don't worry about that, but no, you can't just take a connection off the existing radiator circuit pipework.. That circuit is controlled via your house thermostat so your pond would also be.

    Without knowing what boiler you currently have, how you generate hot water to taps, and the pipework arrangement I'm unable to tell you if/where you can connect to the system I'm afraid. You need to check if your boiler has the ability to run 2 heating zones and whether you are actually using 2 zone control ie. stats both upstairs and downstairs. If you have got a spare heating zone you can use that for the pond.

    As for the ASHP, in an ideal world you would bring a dedicated circuit to serve it but it's not compulsory as far as I know. Electrics aren't really my thing but it would depend on whether you have any spare capacity on the existing supply to the filter house, bearing in mind what you already have connected/running.

    No worries about the U value calcs.. I've got calc sheets that I just put basic info into and the U value is automatically generated. I just need to know what each element is and how thick ie wall, 200mm timber, 15mm insulation. It's the glazing and the roof where the majority of heat is lost which is why I suggested using a double layered cover with an air gap.

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    Member Rank = Sansai Point's Avatar
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    If you decide a dedicated boiler is the way you want to go, you should look for the smallest system boiler you can find. I just had a very quick look and found a 12kW one (I don't think you can buy any smaller than that), which is plenty big enough for your pond heating. No calcs needed really.

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    Senior Member Rank = Rokusai Simon Fish's Avatar
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    Worcester do a 9kw Greenstar

    Yes the Hydrogen boilers are still in the planning, but are more than a concept on a drawing board.

    30m is a big pipe run, lots of factors have to be calculated in. As to the pipe already being covered, before being tested??��

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    Member Rank = Nisai Smiffy's Avatar
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    Relatively speaking, you are defo an expert!!

    I think we need to forget about hooking up with my existing boiler as itís about as far as you can get from the filter house and I do have two thermostats on it already.

    I will put the wall specs etc together and post them back tomorrow.

    Thanks for your help.

  27. #17
    Member Rank = Nisai Smiffy's Avatar
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    Quote Originally Posted by Simon Fish View Post
    Worcester do a 9kw Greenstar

    Yes the Hydrogen boilers are still in the planning, but are more than a concept on a drawing board.

    30m is a big pipe run, lots of factors have to be calculated in. As to the pipe already being covered, before being tested??��
    Thanks Simon, Iíll look into it.

    Iím confident the builders were careful fitting the pipe and there are no joints so hopefully not too much to go wrong. However, Iíll get it tested before I buy the boiler just in case.

    Cheers

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    Hi Smiffy, as above, the smallest boiler you can buy seems to be the 9kW Worcester system boiler that Simon mentioned. Your pond heat loss won't be that much so you may as well forget about the calcs and just buy the 9kW boiler. The boiler will also need to be ramped down so it provides less heating otherwise you risk fast temperature rate of rise which won't be good for the fish, and the boiler will cycle too often which reduces its lifespan.

  29. #19
    Member Rank = Nisai Smiffy's Avatar
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    Quote Originally Posted by Point View Post
    If you decide a dedicated boiler is the way you want to go, you should look for the smallest system boiler you can find. I just had a very quick look and found a 12kW one (I don't think you can buy any smaller than that), which is plenty big enough for your pond heating. No calcs needed really.
    Hi Point,

    My pond is a very similar size to DTF's but I have got 2 windows. As per the attached photo, only two of my pond walls are fully exposed.

    The dedicated boiler is still my preferred choice at this point and the 9kW Worcester looks pretty small and compact (cheers DTF) although I'm sure I have enough room for something a little larger should the 12kW options be better.

    As per your previous advice "Don't get a combi boiler, just get a system boiler which will include an expansion vessel and primary circuit pump (the heating circuit) within the unit."

    Are the following boilers suitable?

    https://www.plumbnation.co.uk/site/w...tural-gas-erp/

    https://www.plumbnation.co.uk/site/v...tural-gas-erp/

    Which of the above would be your preference (or other options) given that the physical size and price are similar?
    I have got a mains water supply all ready to connect assuming it will be pressurised in this way?

    Cheers
    Attached Images Attached Images

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    Member Rank = Nisai Smiffy's Avatar
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    Quote Originally Posted by Point View Post
    Hi Smiffy, as above, the smallest boiler you can buy seems to be the 9kW Worcester system boiler that Simon mentioned. Your pond heat loss won't be that much so you may as well forget about the calcs and just buy the 9kW boiler. The boiler will also need to be ramped down so it provides less heating otherwise you risk fast temperature rate of rise which won't be good for the fish, and the boiler will cycle too often which reduces its lifespan.
    I guess that makes life a bit easier. Hopefully the fitter will know what that all means re ramping down. I will put together a brief based on the advice given and post it back here first for scrutiny.

    Wickes do loads of different polycarb sheets. As per your previous comment (which I damned if I can find) do you advise going with 10mm thick panels and fabricating two layers with an air gap of say 10mm? It would be easier to use the 25mm multi-wall/triple-wall if feasible?

    Typical available options... https://www.wickes.co.uk/Products/Bu...=&25+mm=25+mm#

    Thanks agin.

 

 
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