Megaflo or no?

[Natt3]

We are ready to go ahead with a loft conversion, but stalling because we're totally confused about what we do or don't need in terms of boiler / megaflo to go with it.

We currently have one bathroom - will have two post-conversion. Our pressure (combi boiler) is good - but we're told it's possible we'll have problems with 'flow' (what's the difference?) using two bathrooms.

It seems like a megaflo would be a huge upheaval / involve ripping up the floor on ground level. Does it sounds like it would be worth it?

Any expert or experienced advice would be huuugely welcome.

Thanks,

Natt

 

[dcawkwell]

It depends on the location of your current combi.
I would suggest doing the conversion and see how you get on with your existing boiler.

It is unlikely a standard combi would drive more than one outlet at the same time of hot water but depending on your water pressure and flow this may not be a problem. Two showers at once forget it. But then if only one person showers at once it isn't a problem.

After conversion if you are unhappy with hot water delivery you could
upgrade the existing combi to something like a big ravenheat that can do 17 litres a minute of hot water. Still wouldn't do two showers at once.

Other boiler like the glow worm ultrapower are a cross between combi and unvented tank all in the nice one box. But if your existing combi is just in the kitchen then it wouldn't be suitable unless in a corner that you can move into a cupboard or something.

Regardless you should measure your flow rate of litres per minute you are currently getting of mains cold. Measuring the pressure would also be good.

 

[JohnD]

fill a bucket at your kitchen cold tap, time it, calculate how many litres per minute you get, tell us.

 

[Natt3]

Thanks! Experiment done - it's just under 11 litres per minute. Is that good news or bad??

 

[dcawkwell]

Thanks! Experiment done - it's just under 11 litres per minute. Is that good news or bad??

No bad. Ideally for a combi you should get about 20 litres a minute.
You only have enough flow for cheap combi boiler.

Next thing is to measure pressure. If you have reasonable static pressure
you can improve things with a cold water accumulator tank
that will store cold mains at pressure.

The alternative is vented cold and hot tanks and a pump for pressure.

But living in London as suppose you can't expect a reasonable water supply.

 

[JohnD]

11lpm will be very disappointing if more than one person tries to draw water at the same time.

For example, you could fill a bath in about nine minutes (bit slow) but if someone else is trying to have a shower at the same time, it will be a very weedy shower, and the bath will take about eighteen minutes to fill, because you will get about* five and a half litres per minute each.

Similarly the flow at any tap will drop if a WC is flushed, a dishwasher or washing machine starts to take in water, or someone turns on one or more other taps within the property.

You have quite likely got an old half-inch supply pipe in lead, iron or copper. If you dig a trench to the roadside and run a new pipe in 25mm or 32mm plastic, you will very likely get a vastly improved rate of supply, and a Megaflo then becomes a reasonable idea.





*in practice, it is unlikely that flow will be shared exactly equally between all outlets.

 

[Natt3]

Thanks so much.

If we did change the pipe and improve flow then... would that itself not allow e.g. two decent showers at once? With increased ltrs per min from the pipe, what extra would we get from the megaflo?

N

 

[Agile]

After conversion if you are unhappy with hot water delivery you could
upgrade the existing combi to something like a big ravenheat that can do 17 litres a minute of hot water. Still wouldn't do two showers at once.

You must be the only one to recommend Ravenheat!

 

[CBF]

ravenheat

OP tbh at 11 ltrs/min neither a combi or a megaflow is suitable for you, stick with a roof tank (you might need a bigger one or two linked together) fit a bigger cylinder & use a pump for the showers

 

[dcawkwell]

After conversion if you are unhappy with hot water delivery you could
upgrade the existing combi to something like a big ravenheat that can do 17 litres a minute of hot water. Still wouldn't do two showers at once.

You must be the only one to recommend Ravenheat!

Installed a couple. I've found them good and solidly built.
Unlike some of the cheap plastic nonsense they put in boilers now.

 

[Natt3]

Hello all - so six weeks on...

I've had the supply pipe upgraded: flow rate now about 25 ltrs per min.

Naively I thought this would mean plenty to go round, and no more worries about two taps at once.

In reality, I can really see the increased flow in the kitchen - but the bathroom doesn't seem much different... and when running the bath and turning on the bathroom tap, there's still a major drop off.

When I asked the guys who upgraded the pipe about this they said that will happen because both outlets are on the same run - and I can improve this by 'balancing the system' (I think that was the phrase).

Can anyone explain what that's about?

Thanks a lot,

N

 

[JohnD]

it sounds like the HW pipes have been run in 15mm

this is a trick used, especially for bathtaps, because the average combi boiler will not be able to heat 25 litres per minute - you would just get a good flow, but lukewarm water. An average combi can deliver about 12 lpm, it will be cooler in winter when the incoming supply is cold, maybe as much as 16 for a bigger combi.

If you do go for a Megaflo, because the boiler will heat it in advance of use, and they are usually quite big, you might have 250 litres of hot water in it ready for use, and if you run a 22mm pipe to it, all the way from the (new, larger) stopcock, it will deliver hot water at an excellent rate. I know someone with a Meg whose hot bath tap delivers 20lpm, which is great.

Have a look at your pipe runs, any sections of 15mm pipe will throttle the flow, and especially service valves and stopcocks, which are very restricting if not oversized.

 

[Natt3]

Thanks John that's very useful.

Would I be right in thinking that because the total flow is now decent, when we have a second bathroom (on a different 'run'?) both bathrooms should be usable at the same time (without a megaflo)?

Thanks again.

N

 

[JohnD]

if you have a combi boiler which can only deliver (say) 12 litres per minute of hot water, then you will get either 12lpm of hot, or 25lpm of cool.

I can't see that either will be much use if shared between two bathrooms.

Bigger combis are available at extra cost, including some which store some hot water and can deliver more for a limited period.

IMO combis are not suitable for homes with more than one bathroom.