CH change: large house & 2 boilers

[Mjward]

Hello


I am renovating an Edwardian property with a two-storey extension that was built 10 years ago and currently has two boilers individualy covering original house & extension as below:

Original house (system boiler, 10-15 years old)
4 ground floor rooms all with wet UFH
4 first floor bedrooms with one radiator per room
1 first floor bathroom
(+Unheated insulated loft space)

Extension (combi boiler, 5 years old)
1 ground floor kitchen and utility room
1 first floor main bathroom
1 first floor bedroom

My question I hope is a rather simple one:

Given the demands on the original house ie only one bathroom, no kitchen but covers the bulk of the total house size (c350sqm) from a CH perspective, could I happily replace the ageing system boiler with a combi boiler?

Thanks for any help

 

[ShaunCorbs]

If there’s only one bathroom yes but you will have to watch the requirements for the ufh tho

 

[Scott_D]

With a combi every time hot water is needed it will stop central heating.
Unless you are limited on space, best to go for a boiler and cylinder.

 

[Mjward]

Ah that's an interesting point. I'm new to combis and just read up on what you've said ie running hot water will take priority over rads.

In real world situations how noticeable is this? I would guess in a poorly insulated Edwardian property the room temps could drop 1c or 2c after someone had a 30 mins shower?

 

[WC1]

Ufh will give heat up off the slab for a fair old time. I don't think you would notice the heating going off. But a combi will need changed if you add a bathroom in future.
And with a combi if hot is drawn in the kitchen or utility the shower will be affected. And finally, if anyone in my household spent 30 minutes in the shower there would be trouble !

 

[king of pipes]

No kitchen ? And renovating for what purpose please ? Is this a family home or split up smaller units ?

 

[Mjward]

Sorry I clearly haven't explained it clearly. It's one house. The original Edwardian home + a 2010 extension. The kitchen is in the extension ie the boiler that is plumbed to the original property covers ground floor rooms, bedrooms and one bathroom. There is a separate combi boiler that covers the entire extension (Inc kitchen, bathroom, ensuite).

This is a private renovation, to modernise but keep it as a family home.

 

[king of pipes]

Depending on budget I would advise keep combi for downstairs heating and hotwater and a replacement system boiler and unvented cylinder for the upstairs bathroom and any future ensuites . Kop

 

[Mjward]

Great, thank you all

 

[Mjward]

simple solution, use boiler for hot water and another boiler for central heating. Buy a boiler that allows you to control heating flow temperature down to 35 degrees so you can run the ufh. Never have loss of heating when DHW needed, central heating boiler can be switched off 6 months of the year and so extending the life.

Very good idea in principle but unfortunately the original house & extension aren't connected from a plumbing perspective ie to do this would require complete replumb to connect them together in this manner. If I was designing from scratch it would almost certainly be the way forward I think.

 

[Mjward]

I appreciate that but the target here is to reduce the work involved. I believe changing pipework for two completely independent systems through effectively different buildings (original thick stone Edwardian house + modern extension) will be a substantial effort.

 

[Mjward]

Right, finally found plumbers with availability and a couple have come over to check the system. Both had a similar message: replacing system with combi is fine for a one bathroom setup (I'm now mid renovation and have no plans to add ensuite or to renovate again at a later date!)

However, one of them raised the question if whether I would need two separate gas meters. For now this was a thought in his head to which he will investigate but I thought in the interest of time to put it to this forum.

I have a fairly new gas meter with the following information:
Qmax 6m3/h
Qmin 0.04m3/h
V 2.0dm3
P max 75 mbar
G4

The existing combi is a Baxi 630 (20kw) and the planned system boiler replacement is a Bosch 8000 (35kw) but I've looked through the technical specifications for both and to my untrained eye can't see anything about min/recommended gas loads or any numbers that would marry up with those on the gas meter.

1) Is there a way I can find out the gas load requirement for those boilers?
2) Any experience with a house with 2 boilers on one gas mains?
3) Is this only an issue with 2 combis? (as existing house is one system and one combi and can only assume it was fine from the previous owner)

Thanks

 

[Mjward]

adding a picture of the exact meter I currently have

 

[king of pipes]

Are they the only 2 gas appliances in the whole property ?? A G4 badged capacity gas be meter will pass 6/m 2 of gas a hour roughly 60 kw so providing the pipe sizing is correct and you don't add a hob or range cooker then it's possible to go ahead . Kop

 

[ShaunCorbs]

As above unless you want separate gas bills for each boiler one will be fine provided you don’t have anything else needing gas

 

[Mjward]

Only other gas supplies appliance is the AGA oven. I don't have any documentation for it but Google seems to suggest it only draws 2-3kw so I look to just be about ok with the current meter it seems

 

[Mjward]

Small update, national grid surveyor over last week, took a few photos and I'm expecting an update shortly.

HOWEVER... Eon, my utility providor, installed smart meters today and as part of that fitted a new gas meter, a GS-60B. I can't seem to find a kw capacity but where it says Qmax 6m3/h am I right to assume this is no greater capacity than the G4 it replaced?

Was crossing my fingers I had got lucky with a free upgrade but suspect not.

 

[king of pipes]

No it's the same as your old one I'm afraid .

 

[Mjward]

No it's the same as your old one I'm afraid .

Thanks for confirming. Back to National Grid then! 👍

 

[Mjward]

Have I got extremely lucky or is this the norm for a quote from the gas people? Have specced to go to a U16 which is great but they have applied a discount to match the cost breakdown ie are doing it for free

 

[ShaunCorbs]

Quick do it

 

[Mjward]

Quick do it

Lol don't worry, immediately clicked accept!😜🤣

 

[king of pipes]

Bite their arm off 😂

 

[Mjward]

Bite their arm off 😂

They might struggle to dig the hole!

 

[Mjward]

Just a quick one...as I'm getting new boiler installed in next few weeks and might take a month or two for the upgrade...

What happens if I have appliances fitted that require more than the current supply? I.e. if I run a 35kw and 40kw combi plus an ago (around 2-3kwh), for combined 77kwh on a 67kwh G4 meter, will it be simple lack of power issue or cause appliance damage?

Wondering whether need to postpone boiler install until work done but would ideally have all sorted before winter kicks in