Combination boiler/s for large house recomendations please

[DavidReid]

I have just bought with my partner a huge old georgeon house and I am coming to the stage of needing to source a boiler.

The house is 6 bedroom with tall ceilings and single pain glass which I cant afford to replace for the moment. It also has a cellar which needs heating. Cavity wall insulation and will have the recommended wall and floor insulation

I have calculated that I need 32Kw of heat to heat all rooms (i.e the sum of the heat rejection needed for each room). But this doesn't include and heat loss through pipes. Of which there will be 2 runs of at least 15m to the last radiator on top and bottom floor from the boiler. So I am thinking I will need something like 35 Kw total.

Ideally we would like a combination boiler capable of this output but I cant find any, even those stating 40Kw output seem to be 40Kw of peak hot water output and approx 28 Kw CH output. We use power showers and have no need for a huge amount of stored water hence looking for combination boilers.

So my option as I see it are 2 pipe system:-

1. To ask on here if anyone can recommend a combination boiler capable of 34Kw CH output.

2. Use 2 smaller 30 Kw boilers which could be used in two different ways (we have plenty of room for them)
i. Split system top and bottom floor
ii. Twined together to feed both top and bottom floors.

I prefer option 2ii as it has several advantages (in my mechanical engineer head), 1 the whole system could still operate at 50% capacity if one of the boilers were turned off or failed (which seems to happen often with my experience so far of combination boiler with Pro instal). The plumbing would be simpler, I think the waterflow would also be higher. The hot water could also be run just from one of the boilers as we dont have a high demand so that CH output from both boilers is not interrupted by the need for hot water.

I have asked advice from a local plumber but I an not convinced he is right hence my question on here.

I will be plumbing it myself so any advise/ critism is welcome.

3rd question. Will the gas flow through the meter be sufficient to allow two boilers to start together of is this something else that will need looking at?

 

[simond]

You could put in an ACV heatmaster 35tc.

It seems to tick your boxes. The mains water supply will be paramount in any mains fed boiler, you will need around 40l/m to extract the best performance from this boiler.

It is not a DIY proposition and knowing ACV you will find the manufacturer disinterested in helping a DIYer. Needs a pro really.

 

[mehran]

the rinnai twin flow sounds just the ticket for you. it is a 32kw ch boiler(though i very much doubt you would need all 32kw of the output)

and a 56kw water heater

the best water heater on the market in my opition and one of the best ch boilers around.

www.rinnaiuk.com/Updates-18-09-08/A4 Twin Flow.pdf

 

[Agile]

You could use two 24 kW combis.

The installer will check if a single meter would be sufficient.

You have not said how many people will live there.

Do you really need to heat the cellar? Most people dont and its a lot of heat to waste. By all means have rads but keep them or their zone off

If you must waste energy heating the whole house in the coldest weather then its going to cost you about £4000 p.a. Are you ready for that.

You will need two zones if the floor area is over 150 m² but can still have two or threee zones if you choose to.

The maximum power is only needed when its -1° outside.

Sounds a nice house. Is is near Stratford?

Tony

 

[gas4you]

Your power showers will have to be removed if using a combi.

I would second the Rinnai. An Atag in disguise.

 

[DavidReid]

You could put in an ACV heatmaster 35tc.

It seems to tick your boxes. The mains water supply will be paramount in any mains fed boiler, you will need around 40l/m to extract the best performance from this boiler.

It is not a DIY proposition and knowing ACV you will find the manufacturer disinterested in helping a DIYer. Needs a pro really.

Thankyou for the reply, as you say the I dont think the ACV is available outside the trade as i cant find any prices for it.

Presuming the waterfeed to the boiler is 13mm to check the flow I could fit and open a 13mm valve which feeds into a larger container of known volume. If I time the amount of time needed to fill the container I can work out the flow rate (i.e volume /time). I'll test this tomorrow

If its not 40l/m pressumably this can only be addressed by fitting a new water metter that would be the property of the water board so a Pro would be able to do it either? Or do you just size the boiler up to compensate i.e 80% flow 80% output?

 

[DavidReid]

the rinnai twin flow sounds just the ticket for you. it is a 32kw ch boiler(though i very much doubt you would need all 32kw of the output)

and a 56kw water heater

the best water heater on the market in my opition and one of the best ch boilers around.

www.rinnaiuk.com/Updates-18-09-08/A4 Twin Flow.pdf

Thankyou, but I think this boiler is only available to the trade as I cant find anyone who list a price for it so them sullying me seems unlikely.

56Kw water heater sound good

 

[simond]

If you have a house with a few bathrooms you will need a good flow rate because a direct water system has no stored water tank. Water main sizes can vary but 13mm would not be a typical size in the UK. 15,22, 28,35, or 25, 32 etc if plastic are more common. It is the flow rate that matters. A water meter will not improve the flow rate.


I doubt you will be able to find a Heatmaster 35 on the internet as far as pricing goes. If you intend to DIY and want an unusually powerful combi you are asking for trouble. Many registered chaps get uneasy outside their normal comfort zone, you are already in it.

By far the best solution would be to get an experienced professional round with the intention of giving him the work.

Alternatively, get it designed on an internet forum where you can't be certain whether you are talking to an inexperienced DIYer with attitude or a professional. DIY forums do not give a warranty.

 

[DavidReid]

You could use two 24 kW combis.

The installer will check if a single meter would be sufficient.

You have not said how many people will live there.

Do you really need to heat the cellar? Most people dont and its a lot of heat to waste. By all means have rads but keep them or their zone off

If you must waste energy heating the whole house in the coldest weather then its going to cost you about £4000 p.a. Are you ready for that.

You will need two zones if the floor area is over 150 m² but can still have two or threee zones if you choose to.

The maximum power is only needed when its -1° outside.

Sounds a nice house. Is is near Stratford?

Tony

Hello Tony

Thanks for the comments

Maybe I should explain why i am on here asking for advice, my experience so far with central heating engineers has not been good so far. I have not had good results and experienced poor performing systems in all of the houses I have let "pros" spec and I have not been choosing based on price. My last boiler install cost 3k for a 2 bed house and when its working in freezing conditions the house is also freezing. (I.e its crap for the money) not cheap I think you will agree and I specifically asked for it to be "over specified". This renovation also has a tight budget and I believe I would make a considerable saving over a Pro.

This house I am currently working on doesn't have to been done quickly and I am already running all the electrical cabling so while I am doing it and have the boards up, it is easy for me to room by room lay the CH pipework in. I can then get them and the boiler positioned exactly where I want them and ensure nothing is tight, its all insulated resulting in a good system. For example downstairs to is a concrete floor, I want to keep all pipes completely hidden and not by spacing skirting out. So I will be cutting a channel down the hall and into each room to run the CH pipes, very few engineers are going to want to do this as its days of work just doing the channel (i.e expensive). So if I do it myself I get the pipework hidden but with easy access and shorter pipework with a central feed and return runs resulting in a better operating system.

I am qualified to degree level in Automotive engineering so have studied thermo dynamics to a high level and am very practical I can Tig/Mig solder have pipebenders ect. So I really believe that rather than taking another gamble on getting someone in I can do a better job myself. If I am sufficiently well prepared and understand exactly what I am doing (why I am here)

Enough of my ramblings back to your questions:-

2 People will there intially so upstairs a single bedroom/bathroom/study/dressing room will be used. But looking to the future its going to be a family house and will be full at Christmas hence specing it to worst case. In reality you are right I intend to fit Thermostatic valves and 50% of the rooms will have minimum heat for 95% of the time we are in the house.

Yes I need to heat the cellar as its converted to a proper room and if I dont it will get damp and ruin the decoration. But yes it could be colder than the rest of the house.

I am getting prepared for the 1st 4K bill as I have just had a bill for last quarter when only 1/2 the house was heated (it was flats with CH in one storage heaters in the other) and it was 500+.
Its a good point though and I think a serious disadvantage to the twin boiler set up as if my partner is left in control of the timing/set point I can see over 4k bills easily.

The floor area is over 150m squared its approx 230, 30 being the cellar.

Can you explain why it would need to be zoned?

Its not far from Stratford but closer to Coventry though

I have now found the Baxi 40 Kw which can supply 34Kw of CH energy and is approx 1k. Would this cope?

 

[DavidReid]

Your power showers will have to be removed if using a combi.

I would second the Rinnai. An Atag in disguise.

Sorry wrong terminology by power shower I mean electric mains fed shower. I.e no water feed

 

[DavidReid]

If you have a house with a few bathrooms you will need a good flow rate because a direct water system has no stored water tank. Water main sizes can vary but 13mm would not be a typical size in the UK. 15,22, 28,35, or 25, 32 etc if plastic are more common. It is the flow rate that matters. A water meter will not improve the flow rate.


I doubt you will be able to find a Heatmaster 35 on the internet as far as pricing goes. If you intend to DIY and want an unusually powerful combi you are asking for trouble. Many registered chaps get uneasy outside their normal comfort zone, you are already in it.

By far the best solution would be to get an experienced professional round with the intention of giving him the work.

Alternatively, get it designed on an internet forum where you can't be certain whether you are talking to an inexperienced DIYer with attitude or a professional. DIY forums do not give a warranty.

Thanks for the comments, the main water feed into the house (boiler feed could be taken directly of it) looks to be 28.

My comments about water meters I meant I do have a water meter fitted and if I find I dont have 40 l/m can a larger flow rate water meter be fitted as it must pose a restriction to the flow? Upgrading pipework to a larger diameter isn't an option as it runs under a drive I dont own.

Dont get me wrong I am sure if I new someone I had confidence in to do the job I would probably ask them to spec the system but as it is I dont therefore I want to understand the system and what is needed. The forum are a good way of getting other opinions which raise further questions. At the end of the day I would prefer it to be my mistake than a mistake made by someone I paid alot of money to do the job.

I will probably end up getting to the point where I find the boiler I want and find someone flexible enough that they supply and fit the boiler/flue ,gas pipe but I run the pipework (CH and HW). Then we commission it together as I believe I cant legally touch the gas pipe and need a registered corgi engineer to fit the boiler for it to be warranted.

 

[glasgowgas]

you say you dont want a large store of hot water you utilise power showers ( you edited to clarify electric mains water showers)

so why do you want i mega combi to supply all the homes hot water?

personally i would split the system

2 totally seperate system boilers. 1 doing rads only say for upstairs

the other one feeding an unvented cylinder and rads.

you say you dont want a large hot water store but with 6 bedrooms (thats potentially 12 occupants) that would be an awful drain on the best of combis.

going with an unvented cylinder you will also have electric immersion backup

just a thought

 

[DavidReid]

you say you dont want a large store of hot water you utilise power showers ( you edited to clarify electric mains water showers)

so why do you want i mega combi to supply all the homes hot water?

personally i would split the system

2 totally seperate system boilers. 1 doing rads only say for upstairs

the other one feeding an unvented cylinder and rads.

you say you dont want a large hot water store but with 6 bedrooms (thats potentially 12 occupants) that would be an awful drain on the best of combis.

going with an unvented cylinder you will also have electric immersion backup

just a thought

Hello

The main reason for the Mega combi is cost, its simply cheaper to have a big single than a small and a medium and it will be cheaper to run a single over twins.

I am still open to the direction I go with the system. The reason for not going over the top with hot water is we will never fill the house. We all shower, we dont hand wash plates so we dont have any need to a huge amount of warm water. In my current house which was converted to a combi we saw a huge cost saving, much of which I think was due to not heating hot water tank every morning and evening. I can see the advantage of the immersion heater though.

Could the unvented cylinder be fitted in loft space?

 

[mickyg]

find out flow rate then come back. No point giving advice until known.