Thermal Store Installation

[electrogear]

Hi,

I've been looking at options for mains pressure hot water in our house, as the vented hot water tank we have currently is not up to the job to run 2 bathrooms / kitchen, utility, cloak toilet etc.

I had a plumber give our system a once over today to see how feasible it is to upgrade, and he thinks the 15mm pipework will need ripping out from the cold water mains supply to the airing cupboard and replacing with 22mm, otherwise I won't have enough flow to supply hot water to 2 bathrooms at once.

Could anyone confirm this? It's not that I don't trust him as he knows his stuff but he said he's not 100% sure if it's definitely necessary and he needs to look into it. Anyone any experience with this?

 

[ianmcd]

yes he is correct if you want to run two outlets at the same time you will need a 22mm feed, I wouldnt advise a thermal store though I would go with a system boiler and an unvented cylinder, thermal stores are very iffy and not a great idea

 

[electrogear]

yes he is correct if you want to run two outlets at the same time you will need a 22mm feed, I wouldnt advise a thermal store though I would go with a system boiler and an unvented cylinder, thermal stores are very iffy and not a great idea

Thanks, I'll look at sorting the pipework first then as I guess I'll need that no matter which system I choose.

What's so bad about thermal stores? I drew my own conclusion from looking online and when I mentioned it to the plumber he seemed to agree it was a better and cheaper idea than putting in a big 42KW combi boiler.

 

[ianmcd]

you wont need a big boiler unless your house is huge . an unvented cylinder and up to a 4 bed normal size probably about 20KW system boiler, and you will have all the HW you require, Thermal stores do not store the HW that you require they just circulate the stored water through a plate heat exchanger just like a Combination boiler

 

[electrogear]

you wont need a big boiler unless your house is huge . an unvented cylinder and up to a 4 bed normal size probably about 20KW system boiler, and you will have all the HW you require, Thermal stores do not store the HW that you require they just circulate the stored water through a plate heat exchanger just like a Combination boiler

It's 4 bed / 2 bathroom / downstairs toilet, 6 sinks/taps total. There's only 3 of us living in it at the moment but got to think long term!... I know how a thermal store works. Seems a better idea to me to have a heat exchanger with cold water mains running through it than to have a big tank with large volume of pressurised hot water which needs proper engineering and regular routine inspections/maintenance.

But... I'm not the expert, that's only my thoughts - so I guess I'll go back to my last question - what's "iffy/not a great idea" about thermal stores?

 

[Madrab]

Hi Electro, as suggested either a thermal store or an un-vented would be what you need.

Both have their pros and cons.

Unvented means storing larger capacities of hot water and if you are thinking long term and more people using it then a large capacity cylinder would be preferred. Excellent HW delivery at mains pressure, but like all HW cylinders that can run out until it recovers. Yes, there are running and maintenance costs with regular servicing required by a qualified specialist. No need for F&E tank so they are particularly suitable where space issue are found, that being said they do have safety devices that require it to be installed with access to a drain.
Thermal stores are a store of water and hot water is produced where the mains water passes through a heat exchanger. It does need constant access to a heat source when the store cools to maintain temp and still needs maintenance though and sometimes scaling in the heat exchanger can be an issue. No regulatory requirements though, so no qualified specialist required to install and service and can deliver adequate HW flow.

Proper design considerations apply and make sure it's planned out well. Part of that design would be increasing supply pipe where necessary and pressure /flow allows, 2 bathrooms would dictate larger supply pipes I would suggest. That though would usually be determined by a pipe sizing exercise by your plumber, that should be definitive.

 

[Dan Robinson]

I love a good Thermal Store. Even have a spare 330 litre one rated to be used unvented on both primary and secondary sides.

IMHO though, unless you have a project, like I did when fitting mine, or a mixture of heat inputs, or maybe some bizarre combination of reasons that an unvented can't be fitted, then I would go with the latter.

Unless you want to make me an offer on mine?

 

[electrogear]

I love a good Thermal Store. Even have a spare 330 litre one rated to be used unvented on both primary and secondary sides.

IMHO though, unless you have a project, like I did when fitting mine, or a mixture of heat inputs, or maybe some bizarre combination of reasons that an unvented can't be fitted, then I would go with the latter.

Unless you want to make me an offer on mine?

Thanks Dan. I am thinking about solar. I always said when I bought a house it would be the first thing I'd do because I was a bit of an eco freak, but I haven't stuck to that! Hopefully in the next couple of years though! It just seems so much cheaper to go TS though, when you take into account a £50/year maintenance contract would be £1000 over 20 years on an unvented system! I am a maintenance tech myself on industrial gas/water/air systems so I'd hope that maintaining a thermal store should be something I could do, but obviously I don't have the right certs to do an unvented system etc myself, I think the costs for installing an unvented system would be double or triple that of a thermal store...?

As for an offer on your thermal store, you're a little too far from me I think. 7/8 hour round trip... and it won't fit in an MX5. Not without removing all of my hairdressing equipment anyway

 

[Dan Robinson]

Solar thermal is dead. Solar PV is dying, and easily integrated to a regular unvented cylinder.

I was refering to log burners, heat pumps, hamster wheels.

Maintaining an unvented is no more than servicing the gas boiler. Which should be done annually.

Biggest mistake people make with thermal stores is oversizing. If you're not inputting secondary heat sources, then they only need to be a fraction larger than an unvented cylinder would be. Otherwise your standing losses become an issue - and don't believe the marketing hype on that front either.


As for round trips..... are you Up or Across?

It is a Specflue Excel 330 litre affair with 100kW plate heat exchanger for hot water. Only used for 2.5 years and removed because i needed the space and my experiment with it was over. Paid over £2K for it.

 

[electrogear]

Solar thermal is dead. Solar PV is dying, and easily integrated to a regular unvented cylinder.

I was refering to log burners, heat pumps, hamster wheels.

Maintaining an unvented is no more than servicing the gas boiler. Which should be done annually.

Biggest mistake people make with thermal stores is oversizing. If you're not inputting secondary heat sources, then they only need to be a fraction larger than an unvented cylinder would be. Otherwise your standing losses become an issue - and don't believe the marketing hype on that front either.


As for round trips..... are you Up or Across?

It is a Specflue Excel 330 litre affair with 100kW plate heat exchanger for hot water. Only used for 2.5 years and removed because i needed the space and my experiment with it was over. Paid over £2K for it.

I'm up and across from you, East Yorkshire.

A few people have tried to put me off thermal store now and recommended the unvented system but I'm still not sure why the unvented is the preferred option? Is there much difference in efficiency (18KW gas condenser boiler input) or cost (if an installer was to do all the work)? Is it purely that the thermal store is prone to scaling issues?

I've had lots of conflicting advice on which system is best. I started out just thinking about putting a booster pump in, which is by far the cheapest option even if I had to replace it every few years, and I could do it myself, but then I'd probably want to look at increasing the cylinder size anyway so that got me to thinking I might as well go for a mains pressure system. I spend enough time at work around pressurised vessels that I didn't want to have that risk (however small it might be) where my family sleep. That's why I started down the thermal store route, but now I'm wondering if putting an unvented system in the loft might be safer than in the airing cupboard... my plumber is going to love me changing my mind as he's currently pricing up a thermal store system!

I'm a little confused about something else too. My heating man said that he'd need to install a relief valve and tun-dish for a thermal store. I thought that would only be necessary with an unvented system? Is he getting confused, or am I?

 

[electrogear]

http://www.plumbcenter.co.uk/en/hea...ia-megaflo-eco-plus-indirect-cylinder-300ltr/

I think this would be about the right size, but very pricey! I'm guessing you could add another £1000 to that with installation, expansion tank, PRV/TRV, TCV etc? This has turned into a much bigger job than I thought! Started off at about £250

 

[bernardgreen]

but I'm still not sure why the unvented is the preferred option?

Good point. expecially as some plumbers prefer unvented and others prefer vented. Yet most seem unable to justify why that is their preference.

 

[Dan Robinson]

Standing losses were the biggest issue I found. Low head systems breed Sludge too.

You have to keep the thing hot all the time.

Unvented over vented is very much application dependant. But a dry loft and mains pressure potable water everywhere without the noise of pumps is the main advantage.

 

[bernardgreen]

mains pressure potable water everywhere without the noise of pumps is the main advantage.

Why would anyone want heated potable water everywhere ? The supply of potable water has nothing to do with the heating system. Not unless people want to be able to make luke warm tea or coffee using the hot water from the shower head or the bath taps.

 

[Dan Robinson]

Try and use some alternative thinking FFS.