Ask a plumber/heating ‘engineer’ anything
Discussion
dhutch said:
Well yes and no, an unvented tank takes up the same sort of space as the vented tank?
The cold water header is usually out of the way, and the centre heating header small.
Obviously a combi saves the hot water tank space but has the various drawbacks of a combi.
Sorry, should have given more detail. Its a bungalow, with the tanks (DHW, HW, F&E) in their own airing cupboard which is approx 1.8mx2m and we would like to make that an ensuite. The boiler is downstairs in its own room and that has all the incoming services (gas, electric, 22mm pipework for hot water, CH pipework flow and return etc) and there is space there for a cylinder, or a storage combi.The cold water header is usually out of the way, and the centre heating header small.
Obviously a combi saves the hot water tank space but has the various drawbacks of a combi.
So the plan is free up the upstairs cupboard to make a new bathroom, and relocate the 3 tanks into the downstairs boiler cupboard as a new boiler, and unvented cylinder, and expansion vessel, etc. From open vented CH to sealed.
Hi,
We've recently had a large extension with underfloor heating and replaced all old single-panel rads for cast iron in the exisitng building. We also changed to an unvented cylinder a few years back.
My plumber is highlighting that our old Worcester Bosch Greenstar 24Ri boiler is not intended to run with an unvented cylinder and feels it is also quite underpowered for our building (4-bed semi, large extension with underfloor heating etc).
He thinks I should consider installing a new Greenstar 8000 Style 35kw to meet our needs. He's not giving me the hard sell but equally, I want to sense check the decision.
Questions:
- I'm not sure how old my current one is, it was here when we moved in 10 years ago - would a new (larger) boiler offer significant efficiency benefits?
- Is running a regular boiler with our unvented cylinder a problem?
- Is 35kw the correct power rating? (is 24kw too weedy?)
- Will uprating power solve issues with some rooms feeling chilly, or is that just a balancing issue?
- Is the recommended boiler any good?
Any thing else to consider?
Many thanks!
Pic of old boiler:
We've recently had a large extension with underfloor heating and replaced all old single-panel rads for cast iron in the exisitng building. We also changed to an unvented cylinder a few years back.
My plumber is highlighting that our old Worcester Bosch Greenstar 24Ri boiler is not intended to run with an unvented cylinder and feels it is also quite underpowered for our building (4-bed semi, large extension with underfloor heating etc).
He thinks I should consider installing a new Greenstar 8000 Style 35kw to meet our needs. He's not giving me the hard sell but equally, I want to sense check the decision.
Questions:
- I'm not sure how old my current one is, it was here when we moved in 10 years ago - would a new (larger) boiler offer significant efficiency benefits?
- Is running a regular boiler with our unvented cylinder a problem?
- Is 35kw the correct power rating? (is 24kw too weedy?)
- Will uprating power solve issues with some rooms feeling chilly, or is that just a balancing issue?
- Is the recommended boiler any good?
Any thing else to consider?
Many thanks!
Pic of old boiler:
Edited by DoubleSix on Wednesday 20th March 14:54
I'm a mechanical engineer with an interest in heating, rather than a plumber however...
I've never heard of needing a different type of boiler for an unvented cylinder than a vented one, the venting/expansion arrangements shouldn't make any difference to the boiler demand. There are pros and cons to 'conventional' and 'system' boilers but that's another topic and again not related to cylinder type. See also 'domestic hot water priority' options.
Typically all else being considered a larger boiler running less hard will be worse for efficiency than correctly sized or even undersized one working hard. The only caveat to that is that some modern boilers have better 'modulation ratios' so can turn down their minimum output lower than some older boilers. But this would apply to a new 24kW boiler as much if not more than a new 35kW boiler and is more about avoiding unnecessary cycling at lower temperatures than efficiency as such.
There has not been much technology change in heat exchanger efficiency etc, given yourold existing boiler is already a reasonably modern condensing boiler.
If the overall heat of the house is good, but a few rooms are colder, that is very much likely to be an issue with balancing and or radiator sizing than boiler size. This can be complicated by the different demands of underfloor heating and radiators, as well as many cast iron radiators having relatively poor heat output for their size.
It's highly unlikely that your house's heat loss calcs, assuming these have been been done, calls for more than 24kW from what you describe. But it is that rather than anything else which should be driving your radiator and boiler sizing.
Nb; Combi boilers are (grossly over)sized for their instantaneous hotwater output, but the fact that 35kW combis are prolific seems to convince people they need a huge conventional boiler!
I've never heard of needing a different type of boiler for an unvented cylinder than a vented one, the venting/expansion arrangements shouldn't make any difference to the boiler demand. There are pros and cons to 'conventional' and 'system' boilers but that's another topic and again not related to cylinder type. See also 'domestic hot water priority' options.
Typically all else being considered a larger boiler running less hard will be worse for efficiency than correctly sized or even undersized one working hard. The only caveat to that is that some modern boilers have better 'modulation ratios' so can turn down their minimum output lower than some older boilers. But this would apply to a new 24kW boiler as much if not more than a new 35kW boiler and is more about avoiding unnecessary cycling at lower temperatures than efficiency as such.
There has not been much technology change in heat exchanger efficiency etc, given your
If the overall heat of the house is good, but a few rooms are colder, that is very much likely to be an issue with balancing and or radiator sizing than boiler size. This can be complicated by the different demands of underfloor heating and radiators, as well as many cast iron radiators having relatively poor heat output for their size.
It's highly unlikely that your house's heat loss calcs, assuming these have been been done, calls for more than 24kW from what you describe. But it is that rather than anything else which should be driving your radiator and boiler sizing.
Nb; Combi boilers are (grossly over)sized for their instantaneous hotwater output, but the fact that 35kW combis are prolific seems to convince people they need a huge conventional boiler!
Edited by dhutch on Wednesday 20th March 15:48
DoubleSix said:
Hi,
Questions:
- I'm not sure how old my current one is, it was here when we moved in 10 years ago - would a new (larger) boiler offer significant efficiency benefits?
- Is running a regular boiler with our unvented cylinder a problem?
- Is 35kw the correct power rating? (is 24kw too weedy?)
- Will uprating power solve issues with some rooms feeling chilly, or is that just a balancing issue?
- Is the recommended boiler any good?
Many thanks!
- No. It won't. You're already running an 'A' rated boiler that is still fully supported by the manufacturer. Questions:
- I'm not sure how old my current one is, it was here when we moved in 10 years ago - would a new (larger) boiler offer significant efficiency benefits?
- Is running a regular boiler with our unvented cylinder a problem?
- Is 35kw the correct power rating? (is 24kw too weedy?)
- Will uprating power solve issues with some rooms feeling chilly, or is that just a balancing issue?
- Is the recommended boiler any good?
Many thanks!
- No, not at all.
- 24kw for a system boiler is not weedy. How many radiators? Whats the age of your property and hows the insulation?
- Probably just a balancing issue. Is the system pump man enough?
- Yes that boiler is a very good one.
Thanks!
Some replies to above:
- heat loss calcs? I feel lucky to find a plumber that can be bothered to show up, I've never known one that takes the time to undertake such things or even balance a system properly!! Do they exist?
- 14 radiators (+ underfloor heating of 9mx6m extension)
- Property is dated around 1900, solid wall construction. I have improved insulation under floors and upgraded windows where possible, but it remains an old house with poor heat retention.
- Pump is quite new. Photo below.
Thanks for all the input. I guess I'll ignore his kind offer to sell me a boiler but the current one does seem to cycle an awful lot.
Some replies to above:
- heat loss calcs? I feel lucky to find a plumber that can be bothered to show up, I've never known one that takes the time to undertake such things or even balance a system properly!! Do they exist?
- 14 radiators (+ underfloor heating of 9mx6m extension)
- Property is dated around 1900, solid wall construction. I have improved insulation under floors and upgraded windows where possible, but it remains an old house with poor heat retention.
- Pump is quite new. Photo below.
Thanks for all the input. I guess I'll ignore his kind offer to sell me a boiler but the current one does seem to cycle an awful lot.
Edited by DoubleSix on Wednesday 20th March 20:03
The 24Ri should be absolutely fine with 14 rads, an underfloor circuit and the hot water.
Obviously assuming the boiler and pump is in good health, and the system in general isn't sludged up. The contents of that Magnaclean filter would help assess that.
Balancing isn't hard, can be a little time consuming. But if not done, even to a moderate degree, then some rads will get hot and some simply won't.
Your Ri maybe older than it looks, could be a much a 16/17 years old, but things really haven't moved on a lot. You can still buy an Ri today.
But if it is, then changing it isn't necessarily a daft thing to do. Not sure a combi is the answer though after having an unvented cylinder installed.
Hard to assess and help over the internet I'm afraid. Too many variables.
Obviously assuming the boiler and pump is in good health, and the system in general isn't sludged up. The contents of that Magnaclean filter would help assess that.
Balancing isn't hard, can be a little time consuming. But if not done, even to a moderate degree, then some rads will get hot and some simply won't.
Your Ri maybe older than it looks, could be a much a 16/17 years old, but things really haven't moved on a lot. You can still buy an Ri today.
But if it is, then changing it isn't necessarily a daft thing to do. Not sure a combi is the answer though after having an unvented cylinder installed.
Hard to assess and help over the internet I'm afraid. Too many variables.
Maybe i wasn’t clear, he’s not suggesting a combi (and I wouldn’t have one). He was just suggesting I replace the boiler, retaining my unvented cylinder.
I have spent a fair bit of time balancing with some positive results. But a couple of rooms still remain somewhat chilly. I know it’s not the rads themselves as the rooms have previously got hot, so they are large enough. It’s just with so much work having taken place it’s difficult to pin point what is causing the issues.
I have spent a fair bit of time balancing with some positive results. But a couple of rooms still remain somewhat chilly. I know it’s not the rads themselves as the rooms have previously got hot, so they are large enough. It’s just with so much work having taken place it’s difficult to pin point what is causing the issues.
DoubleSix said:
- heat loss calcs? I feel lucky to find a plumber that can be bothered to show up, I've never known one that takes the time to undertake such things or even balance a system properly!! Do they exist?
They do but it's much easier to DIY all you need is a tape measure and some knowledge of the house construction and with a one off payment of £12 you can do a very accurate job yourselfhttps://www.heat-engineer.com/
I did mine and it's been surprisingly accurate (just bear in mind that the Std ACH (Air changes Hour) in model for me was way too high) Early 1980 4 - bed extended house improved where I can but could do with a bit more loft insulation and heat loss calcs said 4.5 kW/Hr (I've currently got a boiler with a 10kW min so I know all about cycling
)DoubleSix said:
- 14 radiators (+ underfloor heating of 9mx6m extension)
I assume the underfloor heating has insulation underneath?DoubleSix said:
- Property is dated around 1900, solid wall construction. I have improved insulation under floors and upgraded windows where possible, but it remains an old house with poor heat retention.
A heat loss calc will tell you just how poor the heat retention is DoubleSix said:
Thanks for all the input. I guess I'll ignore his kind offer to sell me a boiler but the current one does seem to cycle an awful lot.
That's odd - if the house has poor heat retention and it's heat loss is more than the boiler minimum output it shouldn't cycle at -2 outside temps - it'll cycle as soon as the heat loss is smaller than the boiler min.DoubleSix said:
Two of these in the new extension. Yes, the underfloor works independently of the main house rads which are controlled by a digital wall
stat on the landing.
Fair enough. stat on the landing.
I can well imagine the boiler will have to do a lot of cycling if driving just the UFH, even more so if it split into two zones, but to an extent you will be stuck with that with any boiler and that setup. The best you can do is minimise the time the boiler is feeding a small heating demand.
The flow temp on the boiler is almost certainly set higher than it needs to, and turning this down will reduce the heat output rate of the radiators, which would help balance the rads to the ufh.
I'm looking at replacing my boiler in the next 6-12 months.
I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
Fastchas said:
I'm looking at replacing my boiler in the next 6-12 months.
I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
You can use either a 'system' boiler, or a 'heat only' boiler with either a vented or unvented hot water cylinder. I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
They are basically the same thing, a system boiler is just a box with a heat only boiler (burner and heat exchanger), circulation pump, expansion tank, and zone valve.
Only thing to make sure is that you can set different flow temperatures for supplying the radiators as the hot water tank.
Fastchas said:
I'm looking at replacing my boiler in the next 6-12 months.
I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
I guess you have just two pipes flow and return from boiler to pump with either two actuated valves one for HW and one for CH (S-Plan) (or a three port valve Y-Plan)I currently have a Glow-worm Micron 60FF. Googling this, it describes it as a 'heat-only' boiler.
When I look on Boxt/iHeat etc, the system we have makes the selection of a system boiler. We have a Heatrae Sadia Megaflo, no loft tank.
Boxt/iHeat suggest loft tank systems require a HO boiler.
My heating engineer also says I need a HO boiler.
Who is right, and what boiler would be a good replacement for a 12 rad system, 1 bathroom & 1 en-suite shower cubicle?
Most system Boilers have integral pump and 4 pipe configuration (2 flow and 2 return pipes) depending on how close to the boiler the HW tank is it could be a bit of a pain to run the extra pipes
If you get a HO boiler get one that supports DHWP (Domestic Hot Water Priority) controls and go away from S or Y plan
You only need to spec the boiler for the property heat loss then (no need to oversize it to cope with HW and CH at the same time)
Get the boiler with the lowest min kW you can (reduces cycling)
A quick google tells me the 60FF is non condensing and has a min of 16kW and a Max of 19kW so if this currently heats your home with no issues you don't need to go any larger (a heat loss calc could tell you you could go much smaller if you've improved the house since it was built with DG or CW or additional loft insulation)
My early 80's house (when built had single glazing, a smear of loft insulation 25mm max and no CWI and a 16kW non condensing boiler - I assume sized correctly at the time) We've extended significantly but had DG, CWI, UFI and 100mm of loft insulation and the heat loss calcs say 4.5 kW at -2 so when we replace the boiler in early summer the biggest boiler I'm likely to fit will be 16 kW - I could get away with 11 kW but as we heat the house to a schedule I need a slightly higher output to bring the house up to temp quickly)
All gas boilers since 2005? have needed to be condensing so you'll need a condensate drain fitted
Would people recommend power flushing?
Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
One of the jobs for the summer is to get a new hot water cylinder installed. Would it best to get the system power flushed? It seems most of the rubbish collects in the rads from what I’ve read and obviously I’ve replaced most of them. Or does rubbish still collect in the pipes?
I don’t mind paying for it if I will see a benefit. But if there’s no point as I’ve replaced the rads then no point paying for something for no benefit.
Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
One of the jobs for the summer is to get a new hot water cylinder installed. Would it best to get the system power flushed? It seems most of the rubbish collects in the rads from what I’ve read and obviously I’ve replaced most of them. Or does rubbish still collect in the pipes?
I don’t mind paying for it if I will see a benefit. But if there’s no point as I’ve replaced the rads then no point paying for something for no benefit.
Tailender Investor said:
Would people recommend power flushing?
Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
What did the rads/pipes look like what removed? Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
Magnaflow filter?
Probably all ok?
dhutch said:
Tailender Investor said:
Would people recommend power flushing?
Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
What did the rads/pipes look like what removed? Currently renovating our new home. We have 10 rads and 3 towel rails. We’ve replaced 8 of the rads (all the old ones) so now we have 8 new rads, 2 tall column rads and 3 towel rails. The tall rads and towel rails are probably 5-7 years old.
Magnaflow filter?
Probably all ok?
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