Thermal Store advice

[myleso]

Help. Advice on thermal stores from participants on forums like this is highly varied - ranging from "forget it" to "understand thermal layering". I am not a plumber and need to find someone who does understand what's involved and can specify and install something reliably.

Any tips on how to find someone I can trust?

Installation due in May. Warwickshire project small self-build - to be heated from log boiler / gas backup / thermal store buffer.

After about 15 hours research online thought I had worked it all out :
- Gledhill Torrent T210-OV
- Vaillant EcoTex Plus 428 boiler
- Stratford EcoBoiler 12 (gravity feed)

But after reading negative reviews about Gledhills on this site I am now worried; and aware that there are more details such as correctly sized expansions tank to be worked out.

Any recommendations appreciated.

Myles

 

[petertheplumber12]

I always used to recommend Vaillant, but since the days of condensing I am not so sure anymore, I would now be more inclined towards intergas since they have a good rep for not failing, I am going an a 1 day course with them next month which will give any of their boilers i install a 5 year guaranty instead of three. see if you can get one of those instead it may be a good move.

 

[mickyg]

a 428 sounds a bit big to be running a thermal store. one of the advantages of thermal stores is ability to downsize the boiler, so unless your property needs around 40kw id say its vastly oversized.
Secondly i wouldnt fit a 400 series vaillant, they are reliable boilers but the Glowworm Ultracom hxi is the same boiler but cheaper and with less sensitive electronics. Most heat only boilers in fairness are pretty reliable as there is not so many parts in them. I havent looked at the Torrent design but I always recommend using a thermal store that uses a coil to connect to the boiler so there is no mixing of water in the store with the boiler, thus preventing the sludge issues that played havoc with earlier TS designs. I would also recommend speaking to DPS about your plans, they can custom desing/build a TS to your requirements, which takes alot of the pain out of the research.

 

[hazetimesfive]

DPS is now thermal integration/ specflue

A Pandora style heat bank with pex will set u back around 2k including vat lead time 3-5 weeks

 

[myleso]

a 428 sounds a bit big to be running a thermal store. one of the advantages of thermal stores is ability to downsize the boiler, so unless your property needs around 40kw id say its vastly oversized.
Secondly i wouldnt fit a 400 series vaillant, they are reliable boilers but the Glowworm Ultracom hxi is the same boiler but cheaper and with less sensitive electronics. Most heat only boilers in fairness are pretty reliable as there is not so many parts in them. I havent looked at the Torrent design but I always recommend using a thermal store that uses a coil to connect to the boiler so there is no mixing of water in the store with the boiler, thus preventing the sludge issues that played havoc with earlier TS designs. I would also recommend speaking to DPS about your plans, they can custom desing/build a TS to your requirements, which takes alot of the pain out of the research.

The 428 is a 28 KW boiler - the cottage is for weekend use so we need to be able to blast in the heat on arrival - right size? Thanks for tip about Glowworm.

OK so 'sludge issues'...? My instinct was to go with direct feed TS heating to keep really simple - I guessed an indirect pressurized circuit had more to go wrong. Thoughts appreciated,

I wouldn't know how to specify a TS so looking for a manufacturer that can provide a sensible solution - Gledhill website was good but some reviews worrying.

Thanks for responding.

 

[myleso]

DPS is now thermal integration/ specflue

A Pandora style heat bank with pex will set u back around 2k including vat lead time 3-5 weeks

The Torrent is £1k. Any advice about what's better about a Pandora style? sorry don't understand pex.

thanks for responding

 

[mickyg]

The 428 is a 28 KW boiler - the cottage is for weekend use so we need to be able to blast in the heat on arrival - right size? Thanks for tip about Glowworm.
.

don't do it. There will only be a limited amount of heat you can throw at the TS and system, probably alot less than 28kw. These are the worst possible boilers to oversize and will result in problems if not properly specified. If your gonna get a TS and do it properly, work from the store down. Get that sized for the property and hot water demand, then get a boiler and stove size to suit

 

[SimonH2]

Unfortunately there are (as you've probably already realised) many, many variables - and you'll get as many (if not more) opinions as people you ask.

Boler connection can be direct or indirect.
Direct will mean you can use the full rated power of the boiler (until it's flow temperature reaches setpoint when it will start ranging down). Indirect means you've a heat exchange coil to limit things.
Direct means the store water goes through your boiler, indirect means it doesn't - but then gives you a separate circuit to manage (either F&E tank or expansion vessel and filling loop etc).

Then for hot water you've a choice of thermal store with integral coil - nice and simple, no controls, no lecky needed. Or heat bank with external plate heat exchanger (PEX or PHE) - which needs electric and controls for the primary loop. The external PHE can be much higher capacity than the internal coil, but then you have the complexity and it'll mess up any stratification you might have.

You haven't said what size of property (other than small) or type of heating. UFH is pretty well self contained. With rads you can fit TRVs to all rads and supply with a modulating pump - when rooms are warm, TRVs will close down and pump will back off making for a quiet system. No room stat needed, just a timer for the pump.

You'll need a lot of inhibitor. Check the manufacturers tech specs as the information on the bottles is usually useless - "enough for systems up to 8 rads" doesn't help. The full specs usually quote a minimum concentration so you can work out from the size of the store and a guesstimate of the rest how much you need.

I fitted a Gledhill (170 OV) in the flat a little over 2 years ago - its given no problems ... yet.
The boiler (Vokera Excel combi) was a PITA before, it's been no trouble at all since.

 

[myleso]

Unfortunately there are (as you've probably already realised) many, many variables - and you'll get as many (if not more) opinions as people you ask.

Boler connection can be direct or indirect.
Direct will mean you can use the full rated power of the boiler (until it's flow temperature reaches setpoint when it will start ranging down). Indirect means you've a heat exchange coil to limit things.
Direct means the store water goes through your boiler, indirect means it doesn't - but then gives you a separate circuit to manage (either F&E tank or expansion vessel and filling loop etc).

Then for hot water you've a choice of thermal store with integral coil - nice and simple, no controls, no lecky needed. Or heat bank with external plate heat exchanger (PEX or PHE) - which needs electric and controls for the primary loop. The external PHE can be much higher capacity than the internal coil, but then you have the complexity and it'll mess up any stratification you might have.

You haven't said what size of property (other than small) or type of heating. UFH is pretty well self contained. With rads you can fit TRVs to all rads and supply with a modulating pump - when rooms are warm, TRVs will close down and pump will back off making for a quiet system. No room stat needed, just a timer for the pump.

You'll need a lot of inhibitor. Check the manufacturers tech specs as the information on the bottles is usually useless - "enough for systems up to 8 rads" doesn't help. The full specs usually quote a minimum concentration so you can work out from the size of the store and a guesstimate of the rest how much you need.

I fitted a Gledhill (170 OV) in the flat a little over 2 years ago - its given no problems ... yet.
The boiler (Vokera Excel combi) was a PITA before, it's been no trouble at all since.

Really helpful - thanks. Yes - I want to keep simple - i.e. less components. Property is 800 square foot, 2 bedrooms. As a weekend place it will have groups descending on it so am oversizing the TS/boiler a bit.

Read different things about stratification - does your Gledhill stratify enough? Is it practical in a small TS like this to attempt to achieve 80 at the top and 20 at the bottom - e.g. just heating the top half for HW in the summer?

Myles

 

[mickyg]

Interesting Simon some of the points you list maybe as disadvantages I see as advantages in terms of ongoing maintenance/lifespan etc.
A condensing boiler connected directly to a store imo is a disaster waiting to happen. Thermal stores that circulate the same store water through radiators and the boiler are sludge heaven. You can just fit a system boiler to keep it simple on an indirect system re:header tank etc.
re: plate heat exchangers, your right about your points but plate hes are inexpensive and relatively easy to clean.. scaled hot water coils on the other hand............
This one was about 15yrs old. Obviously a water softener would have prevented this, but thats another £600-1000 +ongoing salt and wasted water costs(if on a meter)

Untitled

• mickyg
• 1 Aug 2012
• 2

 

[SimonH2]

Hard to tell exactly as I've not actually lived with it myself (it's rented out). Indications are from when I was testing it that it would stratify quite well - boiler dumped hot in at the top and the bottom tended to stay fairly cool (rad return temp).
I fitted a TMV in the boiler return so as to keep the temperature high enough to avoid condensation n the non-condensing boiler - that means it doesn't have an issue of potentially taking cold water from the bottom of the store, heating it to part hot, and then mixing it with hot water in the top of the store. In practice, I suspect this isn't likely to be too much of an issue - though I've noticed the boiler in the house (BG badged Worcester Bosch) can like to run at naff-all power for a few minutes in trap filling mode after a power off which would really mess up any stratification.
Boiler is run from a single stat about 1/2 way up the store, so by default you'll tend to get the upper half heated by the boiler - and it'll shut off once the hot water pushes down and reaches the stat.

Check the docs for the version you are considering, if it has a boiler connection part way up, then that will limit the gas boiler to only heating that store above that.

Obviously, if you get a good burn going in the log boiler, then you can heat the whole store.


TBH though, since you aren't using any "low grade" heat sources I doubt if the stratification makes much difference. If there were (say) solar panels then being able to keep the bottom of the store cool would mean being able to gain something from the solar panels on moderate days as well as bright ones.


Oh yes, on gas boiler sizing, it's hard to oversize ! You don't have the constraint of trying to range down to whatever the heating system needs as it will simply burn for shorter burns at a higher rate. If you get the system set up nicely, it'll mostly run at full (or nearly full) power or nothing.

 

[SimonH2]

This one was about 15yrs old. Obviously a water softener would have prevented this, but thats another £600-1000 +ongoing salt and wasted water costs(if on a meter)

Untitled

• mickyg
• 1 Aug 2012
• 2

I guess a lot depends on the specific situation. Up here we don't have hard water so it's not a problem - but I do recall when I was at uni always finding sediment in the teapot as the kettle had got so bad the lumps were flaking off. I did have fun descaling that - thinking it was a bit slow and "perhaps a little heat would speed up the process" (electric kettle, add a little heat, ... ) - it did speed up somewhat and was quite an impressive amount of "foam" that erupted out of the top

Just a thought on descaling ...
Would a dosing pot upstream of the coil work - just add a pint of vinegar, leave a hot tap dripping to let it diffuse through the coil for an hour or two, then open tap to flush out ? Obviously done more frequently that "after 15 years". Or is that too naïve ?

 

[RWhites]

I'm with Simon. A well set-up thermal store will take a higher capacity boiler than might be considered 'normal' for the property concerned. The only difference will be a faster recovery time.

Personally, I'd favour a direct system rather than indirect - otherwise you'll find the boiler will modulate down, and what I've said above would be wrong. I think you'll find a few searches on here will clarify that direct is definitely better than indirect.

I've got a Glow Worm Ultracom 24 HXI. A 'full store reheat' (in reality approx 2/3rds of the 350lt store, lifted from 55deg to 80deg) takes about 11minutes of the boiler going at full pelt. Longer if there is high heating / hot water demand.

With mine, to avoid the 'sludge bucket' issue, I've peppered it with Magnacleans - one on the boiler return, one on the rad flow, one on the rad return, and a big one on the solid fuel back boiler gravity circuit.

When I was doing my research I was tempted by Gledhill. I eventually opted for Heatweb/Excel/Specflue Heatbank because a lot of the systems and plumbing is pre-installed. At first glance, they look expensive, but will save a lot of labour time, and include a lot of parts you'd have to add to the Gledhill (from memory).

 

[SimonH2]

I eventually opted for Heatweb/Excel/Specflue Heatbank because a lot of the systems and plumbing is pre-installed. At first glance, they look expensive, but will save a lot of labour time, and include a lot of parts you'd have to add to the Gledhill (from memory).

Except that most of this stuff that comes pre-plumbed/pre-wired on the heatbank doesn't exist on a thermal store !
In it's basic setup, the thermal store has cold in and hot out - with the TMV pre-plumbed so there are just two pipes to connect. Then add F&E tank if it's not built into the top of the store, and connections (2 pipes each) for boiler, CH, etc.
In my install I chose to add TMV on boiler and CH. Only the boiler one was really needed (to prevent condensing in the old boiler).

It is true though that they have different specs. I considered a DPS heatbank - but thought them a bit pricey and a bit complicated (important when failure means your tenant refuses to pay rent).

 

[RWhites]

I eventually opted for Heatweb/Excel/Specflue Heatbank because a lot of the systems and plumbing is pre-installed. At first glance, they look expensive, but will save a lot of labour time, and include a lot of parts you'd have to add to the Gledhill (from memory).

Except that most of this stuff that comes pre-plumbed/pre-wired on the heatbank doesn't exist on a thermal store !
In it's basic setup, the thermal store has cold in and hot out - with the TMV pre-plumbed so there are just two pipes to connect. Then add F&E tank if it's not built into the top of the store, and connections (2 pipes each) for boiler, CH, etc.
In my install I chose to add TMV on boiler and CH. Only the boiler one was really needed (to prevent condensing in the old boiler).

It is true though that they have different specs. I considered a DPS heatbank - but thought them a bit pricey and a bit complicated (important when failure means your tenant refuses to pay rent).

Pre-installed PHX for HW. With TMV on output.
Pre-wired pump for boiler, & pre-plumbed TMV for constant temp boiler return - which you've added.
Pre-wired pump for CH.
Pre-wired buffer stats for part-reheat, or full reheat, and programmer to determine which stat is used when.
Centralised wiring centre.
(On mine) 2 x safety devices pre-installed to trigger heat dump if overheating when using solar / solid fuel, so no need for a dedicated heat dump radiator.

Admittedly, not part and parcel of a 'basic' thermal store, but the beauty of a thermal store (to me) is the flexibility to do lots of different things in a neat package.

Adding that lot to a bare tank would be a proper pain - and would take quite a lot of time. It depends or your priorities and budget, but I opted for a more expensive solution to save a heap of time and head-scratching.