Opinions on boiler upgrade plans?

[Harry Bloomfield]

Yes I was thinking about 100L would probably be about right.

I would suggest a 120L cylinder, to allow some small amount of spare capacity. The 10 minutes to recharge your 100L, sounds rather optimistic to me, and 24Kw unecessarily large for a flat - depending on the flats size....

I have a 3 bed semi, 120L open vented, and an modern 18Kw, condensing and modulating boiler, plus a fancy control scheme, in charge of it. It does the heating, or HW, but not both at the same time. It manages to reheat an entire cyclinder, in 25 - 30 minutes, but continues to cycle heating the HW until maybe 40 minutes. Even 18Kw, seems too big for our needs, able to quickly bring the house up to temperature within an hour, even in sub-zero temperatures outdoors. It then quickly modulates down, to minimum output.

The overnight setback temperature is 14C, the day setting is 18C, which begins at 10am. It took it just 20 minutes this morning, to get the 14C up to 18C.

You should be looking for a boiler, which has a good modulation range, the bigger the range, the more efficiently it can work, at low demands, and ensure the maximum Kw, is suitably rated for your property. Too large, and you will pay for it in lower economy.

 

[dannyboy85]

Yes and no. If you want fast recovery on an unvented cylinder you need the power to be able to achieve that. Get a boiler with good modulation, set for hot water priority, with good quality load- or weather-compensating controls. This will give you the day recovery you're looking for, and very efficient heating. If you ask BG to do this though you'll just get a blank stare, they don't have the technical knowledge to be able to achieve such a setup.

EDIT Which bit of Warwickshire? I'm in West Northants....l

Ah I get it now, so it's all to do with recovery time. Not an incredibly importantly factor to me, as long as the tank is big enough to fill the bath... By the time I'm out the bath, it should have reheated again if I need HW for anything else.

P.s. I am in Nuneaton, just next to Coventry.

 

[dannyboy85]

I would suggest a 120L cylinder, to allow some small amount of spare capacity. The 10 minutes to recharge your 100L, sounds rather optimistic to me, and 24Kw unecessarily large for a flat - depending on the flats size....

I have a 3 bed semi, 120L open vented, and an modern 18Kw, condensing and modulating boiler, plus a fancy control scheme, in charge of it. It does the heating, or HW, but not both at the same time. It manages to reheat an entire cyclinder, in 25 - 30 minutes, but continues to cycle heating the HW until maybe 40 minutes. Even 18Kw, seems too big for our needs, able to quickly bring the house up to temperature within an hour, even in sub-zero temperatures outdoors. It then quickly modulates down, to minimum output.

The overnight setback temperature is 14C, the day setting is 18C, which begins at 10am. It took it just 20 minutes this morning, to get the 14C up to 18C.

You should be looking for a boiler, which has a good modulation range, the bigger the range, the more efficiently it can work, at low demands, and ensure the maximum Kw, is suitably rated for your property. Too large, and you will pay for it in lower economy.

Thanks, yes I'm sure it takes no longer than 10 minutes to heat my existing (85L) water cylinder.

This is from the instruction book of the existing Potterton

Hot water always takes priority over central heating during a timed 'On' period. Where a significant volume of hot water is drawn off (e.g. a bath) whilst the central heating is on, the boiler will temporarily shut down the heating until the required store temperature is restored (this will typically take only 10 to 15 minutes).

All the apartments in the 3 blocks were fitted with this 24kw Potterton. It's not a large flat, I have 2 bedrooms (one is tiny) and an open plan kitchen / living area. And then hallway, bathroom and ensuite.

Thanks for the advice on what to look for. There's certainly more to think about than I realised!

 

[Harry Bloomfield]

All the apartments in the 3 blocks were fitted with this 24kw Potterton. It's not a large flat, I have 2 bedrooms (one is tiny) and an open plan kitchen / living area. And then hallway, bathroom and ensuite.

Impossible to be sure, from a description, much depends on room sizes, and heat loss, but 24Kw sounds far too much. Installers are now required to do a heat loss calculation, to justify the size of boiler needed, but many simply do not bother, do not know how to do it. It's crucial, for best economy, so I would seek advice on here, how to go about it, and do your own assessment.

 

[dannyboy85]

Impossible to be sure, from a description, much depends on room sizes, and heat loss, but 24Kw sounds far too much. Installers are now required to do a heat loss calculation, to justify the size of boiler needed, but many simply do not bother, do not know how to do it. It's crucial, for best economy, so I would seek advice on here, how to go about it, and do your own assessment.

Thanks, well according to Zoopla the flat is 55 square metres.

Being a relatively new build (2006) and on top floor, the EPC rating is B.

 

[MNW67]

Thanks, well according to Zoopla the flat is 55 square metres.

Being a relatively new build (2006) and on top floor, the EPC rating is B.

Your central heating requirement might be closer to 2.4kW than 24kW!

 

[Jurassicspark]

24kw is oversized for a small property.

A lot of installers are swapping old boilers with high kw outpit which is not needed.

A matter of two.
Uneducatded labor force.
Money chuggers.

 

[dannyboy85]

I assume the 24kw on the current Potterton is more for heating the hot water more quickly, than it is for the central heating?

 

[Harry Bloomfield]

I assume the 24kw on the current Potterton is more for heating the hot water more quickly, than it is for the central heating?

I would doubt your cylinder will not be able to absorb the heat, as quick as the boiler can push it out, so no. The developers might have had a big discount on 24Kw boiler, and so fitted them. They would not have to pay the eventual gas bills. You need a proper heat loss survey.

 

[dannyboy85]

I would doubt your cylinder will not be able to absorb the heat, as quick as the boiler can push it out, so no. The developers might have had a big discount on 24Kw boiler, and so fitted them. They would not have to pay the eventual gas bills. You need a proper heat loss survey.

Oh yes. I understand the developers at the time (Taylor Woodrow, or something like that) installed them in new estates by the thousands, because they were so quick and easy to install... So I imagine they got a huge discount!

 

[dannyboy85]

I would doubt your cylinder will not be able to absorb the heat, as quick as the boiler can push it out, so no. The developers might have had a big discount on 24Kw boiler, and so fitted them. They would not have to pay the eventual gas bills. You need a proper heat loss survey.

So what I'm thinking then, is I could save gas bills on a new boiler. Not because a new one would be more efficient, but would be better specced to the requirements of my home, and not overpowered?

The lowest one I've seen is 12kw for a system boiler, but I assume they would modulate down accordingly. Who does a heat loss survey then, as it sounds as though most boiler installers just go too high, from what you say!

 

[Harry Bloomfield]

So what I'm thinking then, is I could save gas bills on a new boiler. Not because a new one would be more efficient, but would be better specced to the requirements of my home, and not overpowered?

The theory is, that a boiler trickling along, constantly, is much more efficient than one having to start and stop all the time. An over-specced on, generating more heat than needed, would have to start and stop much more frequently.

The lowest one I've seen is 12kw for a system boiler, but I assume they would modulate down accordingly. Who does a heat loss survey then, as it sounds as though most boiler installers just go too high, from what you say!

As above, the lower a boiler can modulate, then the less it needs to start and stop. Others are better able to advise on how to DIY the heat survey, or who could do it for you. Most installers just seem to make a guess, and choose the next size up, to ensure there is enough heat available. Start a new thread, subject 'heat survey - gas boiler'.

 

[dannyboy85]

The theory is, that a boiler trickling along, constantly, is much more efficient than one having to start and stop all the time. An over-specced on, generating more heat than needed, would have to start and stop much more frequently.

Thanks. Yes, that's another thing that puts me off a combi. It's firing up every single time you turn the hot tap on.

That's got to put wear and tear on it's internals.

I tend to use hot water little and often
I'm one of those who washes up the mug after every cup of tea/coffee, or the plate after every sandwich...

 

[Harry Bloomfield]

Thanks. Yes, that's another thing that puts me off a combi. It's firing up every single time you turn the hot tap on.

That is one of the reasons why combi's are so much less efficient, plus the fact they need to be a higher Kw, because they need to instantly heat the water. As a combi, you would be needing maybe 35Kw, just to heat the water, and the flow, would likely be slower than with your present cylinder.

 

[Jurassicspark]

Thanks. Yes, that's another thing that puts me off a combi. It's firing up every single time you turn the hot tap on.

That's got to put wear and tear on it's internals.

I tend to use hot water little and often
I'm one of those who washes up the mug after every cup of tea/coffee, or the plate after every sandwich...

I've got the kitchen hot water tap supplied by the cylinder while having the WC hot water directly from the boiler.

People often use the kitchen hot water more often so I thought it was much wise to get it supplied by the cylinder to avoid the boiler turning on every minute or so.