Best heating option (combi vs unvented cylinder)

[gt190]

Hi,

Wondering if anyone can give some good insight as I have learned some info from browsing this forum.

Situation – recently moved into a 4 bed detached house. When we purchased it had 3 showers and 4 toilets. We converted one into a utility room but we will in the future (hopefully) have 3 showers again and around 19 radiators (currently have 15).

The house currently has a combi boiler, which obviously means two showers cannot be used at the same time. Kids are young now but as they get older, guests etc we would like a better solution.

Looking online the best solution seems to be an unvested cylinder in the attic.

Currently the combi is in the kitchen cupboard with the gas meter under the stairs. The bathroom is above the kitchen and then attic above that.

Thames water measured outside flow rate at 50l per min and 1.9 bar pressure.

Outside tap is 1.9 bar static pressure and 25l per min. think it dropped to around 1.4bar with a tap on.

Kitchen sink drops to around 12l per min flow

Based on these numbers I am told I would need an accumulator tank along with the cylinder. Which would be some weight in the attic, but apparently joists are good and a platform could be built.

Options would be:

• Keep boiler in kitchen and have cylinder + accumulator in attic
• Move the gas meter to the exterior (candent have quoted around 2k for this) and then put both boiler and cylinders in the attic

Should I:

• Move gas meter to outside, any downside to this other than cost + outlook look. Could maybe increase size of gas pipe here also
• Maybe increase the pipe size between the street and my house? House is 1960s so likely a lead pipe, not sure if the increase flow rates matters..

Any other options here?

One plumber suggested a low loss header on the boiler as well, which I am not sure why.

We plan to stay in the house long term ,so I would like the best solution and future proof. Did a full electrical re wire when we moved in as electrics were partly from the 60s. redecorated most parts apart from the bathroom above the kitchen, which will likely take some damage during cylinder install.


Still waiting for some companies to quote me but I was wondering what people thought.

apologies for the essay

 

[BlueLoo]

Main shower should be priority.
Guest not so much.

I'd put a electric shower for guests and whatever you want for yours.
Reduce the complexity of the installation.
Combi is rubbish for showers given the effects of second users on the pressure.

What about hybrid systems?

PV solar and HW storage with Heat pump doing the majority of the heating. Perhaps have a gas boiler as a boost/back up.

Would not be going full gas for a detached house for a major refurb.

 

[gt190]

i should of added, currently we have one child but plan is to have 3. so 5 of us in the house and we usually have in laws etc saying so ideally would want to be able to run 2 showers at the same time, ideally 3 if needed (when kids become teenagers).

i was thinking to add solar option for the unvesnted tank for if we do solar panels in the future.

not sold on the heat pump systems as of yet (also we have a 60s build with less than ideal insulation).

 

[gt190]

just bumping this one

 

[aveatry]

I am not sure what others will have to say to this but I think a cylinder option may still be affected by a pressure drop if there are too many people using it. As hot water is used the cylinder gets topped up by new cold water at the same time. But I think is still the way to go in your case and has been sugested fit an electric one for guests which is not a bad idea just so you have a shower if the heating fails.

 

[Madrab]

ideally would want to be able to run 2 showers at the same time, ideally 3 if needed (when kids become teenagers).

OK .... that's the key requirement.

1st thing I would focus on is mains pressure - If that is dropping to a dynamic level of ~1.4 bar then that's the area that needs focused on to see what that can deliver under worst case.
Try testing with the pressure gauge on outside tap and open up 3 mains outlets, what does the pressure drop to? A flow of 50L/Min is very high but may only be available due to a really fat district main pipe and where they tested, given the 0.5bar drop in pressure with only one outlet open.

With that significant drop in the pressure I wouldn't look at putting the cylinder in the attic as that would impact the dynamic pressure again, having to lift the water that extra few M. Even installing electric showers could have the same impact on the dynamic mains regardless and would have the same knock on effect if being used at the same time as the unvented, as they are all mains driven.

An accumulator is an expensive approach to satisfying mains water delivery due to the size requirement and once the accumulator runs out, it's back to whatever the mains can deliver until it builds back up again.

 

[gt190]

thanks both.

yep pressure seems to be the problem (thames water said its a problem a lot of houses have and nothing that can be done on their side as the min for them is 1 bar) and the only solution seems to be an accmulator tank e.g. 250l tank with 250l cylinder.
attic is the only place i have space, none downstairs

plan now is to get a heat test done, see what size boiler i need (if i can keep my 32).
get an accumlator survey, see what they can offer
then likely accumlator + unvented in attic.

 

[Madrab]

If going for an attic solution then please don't opt for a horizontal unvented, cylinders are no where near as effective lying on their side.

 

[gt190]

If going for an attic solution then please don't opt for a horizontal unvented, cylinders are no where near as effective lying on their side.

thanks, that is something one plumber told me also. worries me as a plumber i met yesterday who seemed quite good suggested a horizontal cylinder and it made me lose a bit of faith.


if i get a 250l unvented cylinder, would i need a 250l accumlator tank also?

i have asked a few neighbours and the ones with one shower still have an accumulator for the pressure. the ones with more than one shower also have the unvented cylinder as well. people put them downstairs where possible but most have the boilers in the attic.

 

[Madrab]

if i get a 250l unvented cylinder, would i need a 250l accumlator tank also?

Doesn't work like that unfortunately - the accumulator will also serve the balanced cold supply in the house so needs to be able to supply at least 25% more capacity that the HW supply. Size and weight placement will also have to be a consideration if it's in the attic.

 

[flameport]

If you want a backup for the rare circumstances where the heating isn't working, it's called an immersion heater in the hot water cylinder.

Do not buy an electric shower, it's performance will be worse than useless and it will place an excessive demand on your electricity supply which will be incompatible with devices such as heat pumps, EV charging and battery storage.

 

[fixitflav]

OK .... that's the key requirement.

Is an option to keep the combi (so avoiding replacement cost) with an HW cylinder (vented or unvented) heated from the combi CH output using W, Y or S-plan? One shower from the combi HW, others from the cylinder.

 

[gt190]

Doesn't work like that unfortunately - the accumulator will also serve the balanced cold supply in the house so needs to be able to supply at least 25% more capacity that the HW supply. Size and weight placement will also have to be a consideration if it's in the attic.

yes i have been told the beams in the attic look good, but will need someone (maybe building engineer) to deisgn the base to make sure it can take the weight.

so accumulator would need to be 350l if 250l tank, that is quite large. looking online something like this looks like it would work https://www.salamanderpumps.co.uk/products/mainsbooster/tankboost/tankboost-350l/

something like this for the cylinder https://www.heatraesadia.com/products/cylinders-and-hot-water/unvented-cylinders/megaflo-eco-plus

Is an option to keep the combi (so avoiding replacement cost) with an HW cylinder (vented or unvented) heated from the combi CH output using W, Y or S-plan? One shower from the combi HW, others from the cylinder.

current combi is old, but i could get another combi instead of system and maybe run all other taps / washing machine etc from the combi and only the two showers / bath from the tank. sounds complicated though.

If you want a backup for the rare circumstances where the heating isn't working, it's called an immersion heater in the hot water cylinder.

Do not buy an electric shower, it's performance will be worse than useless and it will place an excessive demand on your electricity supply which will be incompatible with devices such as heat pumps, EV charging and battery storage.

yes electric showers never work well in my exp. planning on putting in a solar immersion as we will do solgar panels in the future. likely an electric one as well.

doesnt seem to be a clear cut solution, which seems to always be the case.

 

[BlueLoo]

Don't understand the comment about electric showers being unsatisfactory tbh.

I have a 10kw Mira and even on the coldest days, the flow is more than adequate. Especially so in todays world of energy and water costs.

Granted, it's no deluge but it's more than serviceable.

Especially so as a guest shower.

 

[flameport]

Some people consider a trickling piddle of warm water at 4 litres per minute to be 'adequate' for a shower.
Perhaps it's adequate to make sure your guests never return.

Electric showers are the worst possible shower and the worst possible way to heat water.