Heating System Upgrades

TooCautious

Good Morning All

Looking for advice on upgrading my home heating system please. My apologies, there's quite a bit of data here.

Current system - about 30 years old, Potterton Prima heat only boiler, Fortic tank (no F&E tank in loft), mostly old rads with no TRVs and and old style room stat.

Four bedroom detached house with 4 adult occupants. One bathroom with mixer shower off bath taps, one ensuite shower room with mixer shower.
Plumber tested water flow and pressure with the following results:
Cold tap on its own 18 ltrs/min
Hot tap on its own 14 ltrs/min
Cold tap on upstairs and cold tap on downstairs 12 ltrs/min
Hot tap on upstairs with cold on downstairs 9 ltrs/min
Static pressure 3.5 bar
Dynamic pressure 3.2 bar

Trying to avoid combi boiler as I don't want to remove cylinder and reconfigure system to find that performance is inadequate for our needs, and also I'm looking at installing solar PV in future and would like to use any excess energy to heat the water.

My preferred system would be a system or heat only boiler with an unvented (Mixergy?) cylinder but the plumber who carried out the above tests has said that our mains supply is less than the required 20 ltr/min minimum required and we would be disappointed with the performance. This requirement does seem to be backed up with the research I've done. He has suggested installing an accumulator tank in the garage as a solution but this isn't a cheap addition and I'd rather not lose the space.

Other plumbers haven't carried out any tests and seem happy to fit an unvented cylinder.

Are these my options?
Combi boiler
System boiler/unvented cylinder/accumulator tank
New vented cylinder with new F&E tank in the loft

Can anyone recommend a reliable and knowledgeable heating engineer in the Northampton area?

Thanks in advance.

grumbler

I'm no expert, but what do you call "heat only boiler"? And why do you even consider low-pressure hot water system with a tank in the loft while you don't have a tank ATM? IMHO tank makes sense only if your water supply is unreliable.
Also, what's wrong with the existing boiler and the cylinder  and what do you want to achieve by replacing them?

tacpot12

The other option to look at is keeping a vented system, but adding a pump to provide more pressure, principally to benefit the showers.

A vented system has some advantages:

• They don't need servicing every year (unvented tanks do) 
• It's easier to add inhibitor to the system (you just pour it into the F&E tank).
• Vented cylinders are cheaper 

But they can also waste heat if you get a blockage in the heating system. However, any new boiler will require the heating system to be cleaned before it is installed in order to comply with the warranty, and a magnetic cleaner is usually also required, so the chances of blockages should be low.

Our F&E and cold water supply tanks are high up in the loft (2.85m above the shower head in the bathroom), and our shower is fine. If you can get the tanks high enough, you might not even need a pump.

I'm a fan of vented systems and think they still make sense if you have the height and space in the house. For a flat or apartment, unvented cylinders make total sense.

We had our old boiler replaced a couple of years ago with an Intergas HRE OV. This is a model that is specificed as suitable for open vent systems (The OV in the name means "Open Vent"). We've been very pleased with it. The hot water cylinder was replaced about five year before that when the old one started leaking.  

TooCautious

Thanks for the replies.

In reply 'grumbler',

Heat only boiler is one which heats the water only -  no pump so an external pump and storage cylinder is required. The boiler is becoming unreliable and being 30 years old is pretty inefficient. We also run out of hot water when running a bath, and even when showering sometimes. This is what led me to thinking that a new larger cylinder would be worth it.

In addition to the above, I think the CH pump is on it's last legs and the 3 port valve isn't working as it should.

As you can see, most of the system needs looking at really.

plumb1_2

Have a look at the megaflow pv ready. And upgrade supply to 22mm

TooCautious

Thanks plumb1_2.

Looking at my flow rates and pressure do you think they are sufficient to be able to supply and run an unvented cylinder?

ThisIsWeird

TooCautious said:

Good Morning All

Looking for advice on upgrading my home heating system please. My apologies, there's quite a bit of data here.

Current system - about 30 years old, Potterton Prima heat only boiler, Fortic tank (no F&E tank in loft), mostly old rads with no TRVs and and old style room stat.

Four bedroom detached house with 4 adult occupants. One bathroom with mixer shower off bath taps, one ensuite shower room with mixer shower.
Plumber tested water flow and pressure with the following results:
Cold tap on its own 18 ltrs/min
Hot tap on its own 14 ltrs/min
Cold tap on upstairs and cold tap on downstairs 12 ltrs/min
Hot tap on upstairs with cold on downstairs 9 ltrs/min
Static pressure 3.5 bar
Dynamic pressure 3.2 bar

Trying to avoid combi boiler as I don't want to remove cylinder and reconfigure system to find that performance is inadequate for our needs, and also I'm looking at installing solar PV in future and would like to use any excess energy to heat the water.

My preferred system would be a system or heat only boiler with an unvented (Mixergy?) cylinder but the plumber who carried out the above tests has said that our mains supply is less than the required 20 ltr/min minimum required and we would be disappointed with the performance. This requirement does seem to be backed up with the research I've done. He has suggested installing an accumulator tank in the garage as a solution but this isn't a cheap addition and I'd rather not lose the space.

Other plumbers haven't carried out any tests and seem happy to fit an unvented cylinder.

Are these my options?
Combi boiler
System boiler/unvented cylinder/accumulator tank
New vented cylinder with new F&E tank in the loft

Can anyone recommend a reliable and knowledgeable heating engineer in the Northampton area?

Thanks in advance.

Hi TC.

The flow figures you have quoted are slightly confusing. I presume the 18lpm 'cold tap on its own' flow is from the kitchen sink (or garden tap) so best represents the max incoming mains water rate? And the other 'cold tap' rates, they'll also be from the mains? Ie, none of the house's cold water comes from a stored source? If so, the "Hot tap on upstairs with cold on downstairs 9 ltrs/min" doesn't make sense to me, as they shouldn't affect each other.

Anyhoo, I would agree, for two reasons, that a combi is not your best bet. The first is that an 18lpm mains flow is barely adequate, and would be very disappointing should more than one tap (hot or cold) be used at the same time. And the second - main - reason is that you wish to take advantage of free hot water from PV in the future (and, in this weather, you'd be wondering what to do with it all!). Also, a stored system is future-ready for other heat sources like ASHPs.

So, if going 'stored' hot water, you have the basic option of vented vs unvented. I would again agree that 18lpm is barely adequate for driving an unvented stored system, so vented would seem to make more sense here, unless you manage to improve the incoming supply.

Improving the incoming supply for an unvented system usually has two routes;

1) the first is if there is 'enough' in the mains out in t'road and it's your own delivery pipe that's causing the reduction, in which case a new cold supply pipe to your house could be 'all' that's needed. Any idea what your neighbour's kitchen cold P&F are like compared to yours? And how easy would it be to run a new pipe from the road to your house?

2) And the other way is to boost the incoming supply using an accumulator. Yes, this will take up room - roughly the same as a hot cylinder - and the garage is ideal for this, although a house cupboard should do, or even a bespoke insulated box outside the house. But, it doesn't have to be costly. You actually have a very decent water pressure, so in theory a 'passive' (non-pumped) accumulator could/should do the job. Challis make one with a pressurised membrane inside the tank, and this uses the mains pressure to store a large volume of cold mains water at this pressure, in your case a healthy 3.5bar; this water can then be released at a much greater rate to the house. If the cold mains isn't at a high enough pressure to charge this tank, then a small pump can be added to it to pressurise it, and then there should be no shortage of water at all.

Or, stick with 'vented', but install a CWS as high as possible up in the loft. Since it appears that the hot flow coming from the Fortic is 'not too bad' even tho' it's only fitted on the upstairs floor level, then adding another 6+ feet effective height to this store should really make it fine for most uses. A good quality low pressure shower (designed for 0.2bar or less - look at the Triton Elina for example, 12lpm at 0.1bar is amazing) should give perfectly good results without the need of a pump (hateful things...). Downstairs bathrooms and shower should be absolutely hummin'.

So, personally, I'd explore the 'CWS in the loft' option first, and measure just how high you can locate it/them. You can get 'coffin'-style tanks that will fit high up in the roof apex, and have more than one coupled together for added volume. See how much higher this will be over the Fortic's wee cold tank, and make a calculated decision based on that. If the worst case scenario is that you may need to boost an upstairs shower with a pump, then big deal - fit it in the loft, well sound-insulated, out of sight. But good chance you won't need this. Then chose a good-sized Heat Store-type hot cylinder that will be future proofed.

For the boiler, I'd strongly suggest a 'system' type so that you have no F&E (Flow&Expansion - this is the wee tank used to supply the boiler and rads only, not your cold water) tank in the loft, so the system will be more reliable, easier to monitor, and less likely to corrode.

Change your CH system from what is presumably currently a Y to an S, fit TRVs to the new rads (Smart for some if you like), make the new rads - certainly the ones in the living areas - larger*, and choose Smart controls that work as best as possible with the new boiler to optimise efficient running - to match the boiler's 'protocol'.

*'larger' = operate on a cooler water flow, so the boiler - or other heat source - can operate as efficiently as possible. If the pipes are also in need of replacing, then look at increasing them too, to, say, all 22mm, with only 15mm 'tails' to the rads. If replacing/upgarding the pipes, also look at 'zoning' the house, so that all the bedrooms, for example, can be controlled independently.

TooCautious

Thanks TIW.

Lots to digest there.

fredddddddddddd

Just to throw a combi into the mix, the Viessmann Vitodens 111W is worth a look as it may suit your needs:

https://viessmanndirect.co.uk/Catalogue/Domestic-Gas-Boilers/Vitodens-111-W-Storage-Boilers/Vitodens-111-W-32kW-Integrated-46l-cylinder-ZK06240

(note this combi has an integrated 46L water cylinder)

Together with TRVs and a ViCare Smart Thermostat (which modulates the boiler rather than just issuing on/off commands), I would expect this to be a significant upgrade over your current system - although, the points made above do point out that such a system would not benefit from any future Solar PV, being wholly reliant on gas.

ComicGeek

You've got much better water pressure and flow rates than we have. We have an unvented cylinder and it's fine for running one shower at a time. We just stagger use of hot water and have a rule of not flushing WCs while someone is in the shower.

No point spending lots of money on accumulators or packaged storage/pump sets if you can just manage use, IMO. Can you stagger the 4 showers or are you specifically wanting to run both showers at the same time?

TooCautious

fredddddddddddd - I had looked at this Viessmann boiler as a possibility. The downside is that it's a big beast and won't fit in the current location. But worth considering if I can re-site.

ComicGeek - can I ask what boiler and cylinder you have please?
Yes, we could stagger usage, which we do already really but I was hoping that gong to an unvented cylinder would mitigate that and give a good amount of hot water.