What to replace old conventional DHW and CH system with?

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Having read many, many threads on the pros and cons of changing from conventional to combi systems, I think I may be staying with a conventional system. I want to replace the main components (boiler, tanks, rads) with newer, more modern, more efficient ones.

What combination of boiler/tank would you recommend for a typical 3-bed semi (1 bathroom, 1 through-lounge, very large kitchen/dining area, 3 medium-sized bedrooms)?
 
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GeorgeBainbridge

Having read many, many threads on the pros and cons of changing from conventional to combi systems, I think I may be staying with a conventional system. I want to replace the main components (boiler, tanks, rads) with newer, more modern, more efficient ones.

What combination of boiler/tank would you recommend for a typical 3-bed semi (1 bathroom, 1 through-lounge, very large kitchen/dining area, 3 medium-sized bedrooms)?

Firstly, if your water supply is good enough, reconsider a quality high flow combi. Look at the recent thread on the Intergas. They boast only 4 moving parts. A highly reliable combi. Look at:
//www.diynot.com/forums/viewtopic.php?t=264146&postdays=0&postorder=asc&start=30

If you want a tank, then go for a thermal store (heat bank with a plate heat exchanger) with an internal CH take off coil to eliminate sludge. Fit a modulating CH pump and TRVs all around.
 
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Personally I believe you have chosen wisely. Dependent upon budget you may look at using a completely sealed system, i.e unvented cylinder with system boiler, or conventional appliance with sealed system components added. There are other factors involved with the above, water pressure and flow rate. Or you could use the std 117ltr cylinder and loft based cws tanks.

All these factors you need to talk to your installer about. Also when you talk to an installer see what facial response you get when you mention unvented and s plan. If it's panic be wary.
 
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Having read many, many threads on the pros and cons of changing from conventional to combi systems, I think I may be staying with a conventional system. I want to replace the main components (boiler, tanks, rads) with newer, more modern, more efficient ones.

What combination of boiler/tank would you recommend for a typical 3-bed semi (1 bathroom, 1 through-lounge, very large kitchen/dining area, 3 medium-sized bedrooms)?

Firstly, if your water supply is good enough, reconsider a quality high flow combi. Look at the recent thread on the Intergas. They boast only 4 moving parts. A highly reliable combi. Look at:
//www.diynot.com/forums/viewtopic.php?t=264146&postdays=0&postorder=asc&start=30
IMO the ONLY place for a combi is where the developer is too tight a***ed to design in the 2foot square for a cylinder. Other than the space saving, I consider they have no redeeming features. On the other hand if you like a system with no ability for a backup (ie no immersion heater for when the boiler breaks down) then I guess you'd thing they are good.
If you want a tank, then go for a thermal store (heat bank with a plate heat exchanger) with an internal CH take off coil to eliminate sludge. Fit a modulating CH pump and TRVs all around.
That I will agree with - apart from the second coil that is. If you are suffering from a significant sludge buildup then I think you have other problems to worry about - and perhaps some inhibitor might be in order.

Since the OP already has a cylinder and header tank, then they have the space for a thermal store/heat bank (same thing more or less). As long as you have plenty of insulation to minimise heat loss, then it should vastly improve the efficiency of the boiler - bursts on full heat rather than short cycling with a bypass to raise the return flow above the condensing point as is the case with a directly heated radiator loop.

I posted a story on my install here. When the boiler breaks down, the tenant can switch on the immersion and as long as they don't go too overboard, carry on as normal.
 
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If you want a tank, then go for a thermal store (heat bank with a plate heat exchanger) with an internal CH take off coil to eliminate sludge. Fit a modulating CH pump and TRVs all around.

:rolleyes:

Just ignore the ridiculous comments from GB, he is not a pro, but a troll who has been barred under many aliases.

The only real answer to your question is: find a good RGI, explain your wants and needs, and let him work out what the best solution is.
The only one who can really tell, is the pro who has been on site.
 
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The only real answer to your question is: find a good RGI, explain your wants and needs, and let him work out what the best solution is.
The only one who can really tell, is the pro who has been on site.
And do you have any advice on how to spot a good pro that will understand the difference between a conventional OV cylinder, a pressurised cylinder, a thermal store/heat bank, and a combi and explain the pros and cons of the options suitable for him ... vs the other 90+% who will tell him that only a combi makes sense ?
 
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GeorgeBainbridge

IMO the ONLY place for a combi is where the developer is too tight a***ed to design in the 2foot square for a cylinder. Other than the space saving, I consider they have no redeeming features. On the other hand if you like a system with no ability for a backup (ie no immersion heater for when the boiler breaks down)

Intergas combis only have 4 moving parts are rarely break down. Cylinders run out of water.

If you want a tank, then go for a thermal store (heat bank with a plate heat exchanger) with an internal CH take off coil to eliminate sludge. Fit a modulating CH pump and TRVs all around.
That I will agree with - apart from the second coil that is. If you are suffering from a significant sludge buildup then I think you have other problems to worry about - and perhaps some inhibitor might be in order.

Thermal stores will be neglected. The CH coil eliminates sludge build up, so best have one in to be sure. It is not a great cost.

Since the OP already has a cylinder and header tank, then they have the space for a thermal store/heat bank (same thing more or less). As long as you have plenty of insulation to minimise heat loss, then it should vastly improve the efficiency of the boiler - bursts on full heat rather than short cycling with a bypass to raise the return flow above the condensing point as is the case with a directly heated radiator loop.

Spot on.

I posted a story on my install here. When the boiler breaks down, the tenant can switch on the immersion and as long as they don't go too overboard, carry on as normal.

Great install. I like the insulation box. A thread here recently stated that the new Collins Plumbing and Heating Guide states that DHW only thermal stores use 15% less energy.

How is your installation operating?
 
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GeorgeBainbridge

The only real answer to your question is: find a good RGI, explain your wants and needs, and let him work out what the best solution is.
The only one who can really tell, is the pro who has been on site.
And do you have any advice on how to spot a good pro that will understand the difference between a conventional OV cylinder, a pressurised cylinder, a thermal store/heat bank, and a combi and explain the pros and cons of the options suitable for him ... vs the other 90+% who will tell him that only a combi makes sense ?

Well said.
 
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Just ignore the comments from GB, he is not a pro, but a troll who has been barred under a number of other aliases.
 
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GeorgeBainbridge

I know, unfortunately if he wants me to bite, he's picking on the wrong person. :LOL: :LOL: :LOL:

I find the regulars here do not like others coming in giving advise and tell the outside punters the new guy is a troll or whatnot.

The way they all promote unvented cylinders at every opportunity, putting down other more cost effective ways is not healthy. I detect some vested interest.

SimonH2's installation is great and he thought it all through. Well done Simon. Others should take note.

BTW Michele, keep shovelling the coal :)
 
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Cylinders run out of water.
An indirect cylinder will, but only because the indirect coil has limited capacity. A direct heated thermal store/heat bank won't run out as long as the boiler can keep up. Since many people seem content with the restricted output from a combi, you'd have to draw off quite a bit more to empty a thermal store unless the boiler is fairly small. Even if you have a smallish boiler, the recovery time when you can pull it's full output into the store, recovering top down, will be quite fast.
But then that's part of the system design - if you are supplying a large house and there's the potential for three people to run a bath at the same time then you need to size the store accordingly.
Thermal stores will be neglected. The CH coil eliminates sludge build up, so best have one in to be sure. It is not a great cost.
But there is a cost in system complexity by having a separate circuit. Looking at the relative sizes, if you have sufficient sludge buildup to cause significant problems in the bottom of a store, then it would have blocked all your rads. That's a LOT of sludge, and if you are getting that much then you do have a much more serious issue with your system.
Great install. I like the insulation box. A thread here recently stated that the new Collins Plumbing and Heating Guide states that DHW only thermal stores use 15% less energy.

How is your installation operating?
It's working fine, but I suspect I might need to add a motorised valve to the heating circuit to stop it thermo-syphoning. Because the store is downstairs, there is enough vertical rise for it to thermo syphon in the normal flow direction without the pump running. Not an issue now, but I suspect it might be annoying in summer.

Apart from keeping heat in, the box is there to a) make it tidy and hide all the pipes, and b) restrict access to make it harder for people to adjust things.

In terms of efficiency, once the boiler gets changed (which will be an interesting exercise in itself) for a condensing one, then I reckon the store will really help. Under light heating load, the radiator return loop can be down into the low 20s in temperature. The result is that the store cools bottom-up (the DHW coil also has this effect) and so when the boiler fires up it can draw cool water from the bottom of the store - I anticipate it should rarely fail to be condensing if setup right.

With a conventional system, to maintain the minimum flow required through the boiler, the cool return from the rads is mixed with the hot flow (via the bypass loop) - so I reckon it's probably rare for a boiler to be condensing while running the heating. So you get all the added complexity of a condensing boiler, but none of the claimed savings.

Since my rad loop flow is completely separate from the boiler flow, the modulating pump just sits there quietly supplying only what the TRVs demand - so the TRVs and pump are barely audible.

I suspect that on cost grounds alone, any savings wouldn't repay the investment in a thermal store - but what price do you put on comfort and convenience, not to mention still having heating & hot water when the boiler breaks down ? With a passive DHW coil thermal store, you even still have hot water (obviously limited in endurance) when the electric goes off.


Of course, all this probably isn't helping to answer the OPs question :rolleyes:
 

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