2 combis vs one Megaflow help!

[VioletG]

Hi,

I have moved into a victorian house which was turned into two flats, so I'm in the process of turning it back into a single house.

There are two non vented cylinder boilers, one downstairs and one up. Both with their own tanks and pumps to increase pressure.

I really need to get rid of the downstairs cylinder completely as it's eatting into the living room and the upstairs boiler is in a bedroom.

The changes we are making in phase one will result in one shower and bath upstairs and just a toilet basin downstairs.

Phase 2 will be an ensuite with shower upstairs.

Phase 3 will be a loft conversion to bedroom and bathroom.

I have had so many suggestions my mind is melting.

1. Megaflow installed now in the loft to serve the whole house.

2. Also been told Megaflow should not go in the loft instead it would need to take over a quarter of the bathroom.

3. 2 combi boilers. One serving upstairs and one downstairs.

4. One combi boiler to serve whole house.

The water pressure is meant to be good.

One engineer told me that some won't service a megaflow that is in an attic.

We do have a crawl space which is about 5ft I'm height but was told this would cost more to work in a small space.

I'm at a loss and can't move with my kitchen renovation until this is sorted.

 

[Madrab]

1. Megaflow installed now in the loft to serve the whole house.

2. Also been told Megaflow should not go in the loft instead it would need to take over a quarter of the bathroom.

3. 2 combi boilers. One serving upstairs and one downstairs.

4. One combi boiler to serve whole house.

1) Wouldn't ever recommend using any horizontal HW cylinder (unvented or otherwise), they just aren't suited to working well that way. If it's to be in a loft with restricted space, then a smaller standard cylinder would be the solution with an ultra high recovery PDHW design or normal S - Plan with tandem cylinders. Wouldn't necessarily look at a megaflop either.
2) Where are the current cylinder located and what's happening with that space?
3) Resource and energy hungry option
4) Depends on what it needs to serve

If the final design is to be 3 bathrooms with shower where there will be more than one HW outlet required at any given time then a combi is not a good solution.

Cold mains dynamic pressure and flow is the critical information you need to know to provide a key starting point. Get a pressure gauge on an unfettered cold outlet close to the mains - say an outside tap - and open that tap outside tap and note the pressure. Then open at least another 2 (unfettered if poss) cold outlets, one as high up the building as possible - then take another pressure reading from the gauge. When running those taps, go to the highest open outlet with a bucket and then time running that tap into it over a min and measure the water gathered. May also want to call your water transporter and say you are having a bit of an issue with your mains pressure and could then come out and test please and ask them to advise what the pressure and flow readings are. That'll provide you with what the district mains can supply to the property.

 

[VioletG]

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1) Wouldn't ever recommend using any horizontal HW cylinder (unvented or otherwise), they just aren't suited to working well that way. If it's to be in a loft with restricted space, then a smaller standard cylinder would be the solution with an ultra high recovery PDHW design or normal S - Plan with tandem cylinders. Wouldn't necessarily look at a megaflop either.
2) Where are the current cylinder located and what's happening with that space?
3) Resource and energy hungry option
4) Depends on what it needs to serve

If the final design is to be 3 bathrooms with shower where there will be more than one HW outlet required at any given time then a combi is not a good solution.

Cold mains dynamic pressure and flow is the critical information you need to know to provide a key starting point. Get a pressure gauge on an unfettered cold outlet close to the mains - say an outside tap - and open that tap outside tap and note the pressure. Then open at least another 2 (unfettered if poss) cold outlets, one as high up the building as possible - then take another pressure reading from the gauge. When running those taps, go to the highest open outlet with a bucket and then time running that tap into it over a min and measure the water gathered. May also want to call your water transporter and say you are having a bit of an issue with your mains pressure and could then come out and test please and ask them to advise what the pressure and flow readings are. That'll provide you with what the district mains can supply to the property.

Thank you. Downstairs (flat 1) a bathroom was created and they took over part of the main living room for it, so stud wall. That is where the vented cylinder sits and below it as a pump for the pressure. Above it in a cupboard is the water tank.

I want to put the wall back so it has to go from here.

The boiler itself is in the kitchen.

Upstairs (flat 2) the cylinder is in the bathroom and directly above it in the attic is the water tanks. The boiler is in a room next to it which should be a bedroom.

So again it needs to come out of this bedroom. I don't mind it being in the bathroom as it's quite big.

The pressure upstairs is awful, which leaves the bathroom almost useless. The toilet doesn't even flush properly and the shower pressure is non existent.

 

[dilalio]

What @Madrab said.
If you can sacrifice the space then UV is best, but only if you have decent incoming and not horizontal in the loft.

If you can adapt to only one shower on at a time or get a combi with highest DHW output, do that.

I have 3 showers and can use 2 at once but the difference is enough for us to wait until none are in use - it's no real bother.

You could look at storage combis but they can also slow when tank gets depleted.

Small, fast recovery cylinder with PDHW. Would be best option.

 

[VioletG]

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What @Madrab said.
If you can sacrifice the space then UV is best, but only if you have decent incoming and not horizontal in the loft.

If you can adapt to only one shower on at a time or get a combi with highest DHW output, do that.

I have 3 showers and can use 2 at once but the difference is enough for us to wait until none are in use - it's no real bother.

You could look at storage combis but they can also slow when tank gets depleted.

Small, fast recovery cylinder with PDHW. Would be best option.

I think we could manage one shower at a time if we had to.

If we went combi would something like a Wocester Bosch Greenstar 8000 work? Or is there a better option.

 

[Madrab]

I think we could manage one shower at a time if we had to.

I think that's the key comment - "if we had to" - not really ideal is it, with me it would always have to be - "the best that is achievable"

Of course, a lot of families work with combi's and I would never discount them in given situations but it really is one at a time and don't use another hot tap if possible, as it will affect the experience. It could be considered a stop gap though I guess as a combi can still be used as the heat source of an UV cylinder later down the line

If it can be accommodated and a stored HW option is a real possibility (pressure and flow) then "if we had to" wouldn't cut it for me.

Certainly sounds like you have a gravity system with an open vented cylinder and the lower one is pump assisted but the upper one isn't, so it's just the height on the Cold cistern.

Again though, the key to everything is the pressure and flow and that needs to be understood before anything is decided. As far as the boiler is concerned you will get numerous recommendations for what would be best, personally I'd stay away from WB.

Have any of the trades that have been in performed a survey on the cold mains?? If not then any recommendations are pointless at the moment IMO

 

[VioletG]

I think that's the key comment - "if we had to" - not really ideal is it, with me it would always have to be - "the best that is achievable"

Of course, a lot of families work with combi's and I would never discount them in given situations but it really is one at a time and don't use another hot tap if possible, as it will affect the experience. It could be considered a stop gap though I guess as a combi can still be used as the heat source of an UV cylinder later down the line

If it can be accommodated and a stored HW option is a real possibility (pressure and flow) then "if we had to" wouldn't cut it for me.

Certainly sounds like you have a gravity system with an open vented cylinder and the lower one is pump assisted but the upper one isn't, so it's just the height on the Cold cistern.

Again though, the key to everything is the pressure and flow and that needs to be understood before anything is decided. As far as the boiler is concerned you will get numerous recommendations for what would be best, personally I'd stay away from WB.

Have any of the trades that have been in performed a survey on the cold mains?? If not then any recommendations are pointless at the moment IMO

Thank you. They did do a pressure test using the outside tap and said it was good, as in good enough for the non vented cylinder or a combi.

One has quoted to put it the attic which would be great but another said not to put it in the attic as it would be an access problem if it breaks down. Or if when we do the loft conversion.

The other said we should have two combis and other said one combi would work if it were a high spec model.

So I'm sitting here totally confused.

What I don't want is to eat into a big chunk of a room to accommodate a vented cylinder.

It feels like everyone who comes out has a different opinion.

The loft is massive, my ideal would be to put it up there. It's all boarded and has a window. Access is from the pull down ladder stairs.

Obviously it's more costly but if it can go there I feel it would be worth it.

 

[flameport]

I think we could manage one shower at a time if we had to.

That really isn't the point. You are thinking about compromising the use of the hot water already which indicates it's a failed solution.

A combi is not the answer.
It won't cope once you add additional bathrooms.
When it breaks you have no hot water at all - and don't even think about shoving in a crappy electric shower 'just in case'.
There is no realistic way of using it with solar.
It's entirely useless when a heat pump or other electric heating options are installed in the future.

The loft is massive, my ideal would be to put it up there. It's all boarded and has a window. Access is from the pull down ladder stairs.

Not a problem then. Unvented cylinder in the loft.
Those that claim not to service such things in lofts will be referring to those where it's just been shoved up there with no boarding, lighting or proper access.

The other said we should have two combis and other said one combi would work if it were a high spec model.

Some installer types are obsessed with combination boilers and install nothing else.

 

[Madrab]

Thank you. They did do a pressure test using the outside tap and said it was good, as in good enough for the non vented cylinder or a combi.

Unless they ran other outlets at the same time then that reading is useless I'm afraid, standing or static pressure doesn't tell you what will happend to the cold water pressure and flow when say 2 people are using shower and the washing machine kicks in.

One has quoted to put it the attic which would be great

As suggested, putting a UV into the attic isn't an issue, just don't use a horizontal cylinder as they can be plagued with issues, a med sized ultra high recovery cylinder with PDHW would work fine, as suggested though, good and safe access is required.

I'm back to - you need to get to a good starting point though, as in post #2 - getting that mains dynamic pressure and flow information is critical to making the right decision, especially if the loft is to be used. You need to get someone out that is experience and ask them specifically to do the tests that way, only way to give you that key info.

 

[VioletG]

Unless they ran other outlets at the same time then that reading is useless I'm afraid, standing or static pressure doesn't tell you what will happend to the cold water pressure and flow when say 2 people are using shower and the washing machine kicks in.


As suggested, putting a UV into the attic isn't an issue, just don't use a horizontal cylinder as they can be plagued with issues, a med sized ultra high recovery cylinder with PDHW would work fine, as suggested though, good and safe access is required.

I'm back to - you need to get to a good starting point though, as in post #2 - getting that mains dynamic pressure and flow information is critical to making the right decision, especially if the loft is to be used. You need to get someone out that is experience and ask them specifically to do the tests that way, only way to give you that key info.

Thank you. I don't think anyone who has visited has properly tested it in the way you describe.

I am using which recommended engineers to quote. It was only today that an engineer suggested the issue might not be the pressure but the old lead pipes and it might need a change to the mains.

This is quite a costly venture so I want it done right. Maybe I'm asking the wrong questions when I call them out or I need to find an experienced non vented cylinder engineer. I assume most fit combis.

 

[dilalio]

non vented cylinder

You'd do well to start with what this is?
"unvented" I presume?

 

[Madrab]

This is quite a costly venture so I want it done right. Maybe I'm asking the wrong questions when I call them out or I need to find an experienced non vented cylinder engineer. I assume most fit combis.

You want an experienced central heating engineer that has his grounding as a plumber and don't be shy in asking what level they are qualified to. You are looking for them to tell you (don't offer them the info) they are min qualified to Level 2 and Level3 C&G in plumbing & heating and for you have their their DHWSS (G3 UV) qualification (water regs would help too), that way you should get a qualified plumbing and heating Pro who has completed their advanced hot and cold water systems, has a min of on the tools exp, is qualified to fit and service unvented cylinders and should be well versed in everything the pro's here have been suggesting.

If any professional balks at you asking to confirm (show you) what level they are qualified to, then walk away. I'm chuffed when a client asks to see my quals, I spent a lot of time and effort (and money) obtaining it all and more than happy to show it off if it makes a client more comfortable.

Our trade, unfortunately, is plagued with wannabees, have a go hero's and/or CH boiler chuckers who think they know what they are talking about and cause more problems than they fix. Oh and ask them to confirm how much they are insured for and what they guarantee. You have a lot of work to get done and it won't be cheap, this way you are at least trying to safeguard your investment.

 

[Agile]

I have heard of many who have done all sorts of courses!

But still do not understand dynamic flow rate or know how to measure it.

Simply it is the flow rate which can be taken whilst still having a pressure of say 0.5 bar in the house distribution pipes.

That remaining pressure is needed to operate combi boilers and to get a nice powerful jet out of the shower head to give you that nice tingling feeling on your back in the shower.

 

[Madrab]

I have heard of many who have done all sorts of courses!

Quite agree - but there are fundamental courses and qualifications that a person just wouldn't go through without coming out of the other end without a reasonable understanding of plumbing, it's principles and at least a core understanding of how it all works (including dynamic pressure and flow) - that would be the level 2 and 3 C&G NVQ's, which would normally take a year or 2 to complete. That's why I was quite specific about what to look for and why I said anyone not wanting to show their quals/experince aren't worth using.

We're not talking about state sponsored entry/access courses that a lot of people are forced to take or their money stops and then think they're a professional when they come out the other end and cause mayhem in people's houses, or the sloppy ACS courses that anyone with enough money can get through.

operate combi boilers and to get a nice powerful jet out of the shower head

say 0.5 bar

Have to disagree, that's far too simplistic - No-one's getting a nice (hot) tingly feeling out of the shower @ 0.5bar, especially 2 floors up in the attic en-suite, at the end of a 15mm pipe, with numerous elbows and pushfit connections, in the winter, on the way from a combi that delivers ~12L/Min @ 35deg and then someone else puts on the washing machine and starts doing the dishes.

 

[VioletG]

Thank you. I have found two with the qualifications you mentioned, so I hope to get a clearer steer.

I have one other question, as mentioned we have two vented cylinders. The pressure is great on one shower due to the pump.

Is keeping a vented system a bad idea? I was thinking we keep one with the tanks in the loft. I know we have a loft conversion at some point but the loft is so huge they could stay. Obviously it would need a pump for the pressure.

But are they a bad idea?