Combi boiler flow rate

[sxturbo]

Thinking of having the combi side of my boiler plumbed in (intergas) so i can have mains pressure hot water on demand.

I want to keep my pumped shower as I've never had a shower so nice prior.

The hot water cylinder is vented and I want to keep that for the shower,

This would mean that I only need to heat the cylinder once in the morning before use rather than ensuring it's hot throughout the day at times we need it.

Also this will alleviate the poor performance we get from the taps for the bath and sink, and kitchen sink.

I checked my flow rate and I got 14ltrs in 30 seconds, so 28ltrs per minute.

The static pressure of the mains is 2.8bar.
I haven't been able to dona dynamic test.

My boiler intergas eco RF 24, has a 12ltre/miN hot water rating.

So I presume my flow rate is too much for the boiler. Would I need to install a.restrictor, or does the boiler have its own restrictor built in?

(flow rate edited due to typo, thanks boolie for pointing it out)

 

[lightning]

If you have such good pressure why not go for a unvented cylinder .

 

[sxturbo]

If you have such good pressure why not go for a unvented cylinder .

Cost and servicing.

Its relatively expensive to install, and I don't really need it. Would also mean I need to re-plumb my bathroom to install a shower (at the moment we have an aqualisa pumped shower and it's great) and I don't really want to do that at this stage.

 

[Mottie]

This would mean that I only need to heat the cylinder once in the morning before use rather than ensuring it's hot throughout the day at times we need it.

Our gas heated hot water is on 24/7. We're never short of hot water. We also have a gas hob. Two of us having a long shower each day. You’d be surprised how little it costs when you are just heating water in the summer when the heating is not being used. Literally pennies. I think it would probably cost more if it was on a timer.

 

[sxturbo]

Our gas heated hot water is on 24/7. We're never short of hot water. We also have a gas hob. Two of us having a long shower each day. You’d be surprised how little it costs when you are just heating water in the summer when the heating is not being used. Literally pennies. I think it would probably cost more if it was on a timer.

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It's more about getting mains pressure to the other taps in the house.

Now my hot water cylinder heats up from cold in 40 minutes or less it's not to bad. (There was a range rate adjustment needed in the boiler)

 

[Mottie]

It's more about getting mains pressure to the other taps in the house.

Ah yes, we have unvented. Before that, whenever our daughter stayed over and had a shower, she said it was like someone spitting on her!

 

[Agile]

The flow rate is determined by how much you turn your taps on. The boiler's flow rate of 12 li/min is the flow rate which it can heat up. If you take a higher flow rate then you will just not get such a high water temperature.

However the HW heating coil in the boiler is relatively small diameter and that will restrict the HW flow rate a bit.

If you really did have a problem with your good water supply then you could fit a pressure reducing valve on the cold water supply into the boiler. They are only about £16 and you could set it to give say 1 bar output.

 

[sxturbo]

Thanks agile, I wasn't sure if the boiler would just automatically reduce the flow rate down to its maximum or not.

 

[Agile]

People with combi boilers and a good water supply pressure quickly learn to only set the flow rate of the tap to what the boiler can heat.

Typically only 9 to 14 litres per minute depending on the power of the boiler for a 35 degree increase in the water temperature.

 

[Madrab]

Some boilers already have flow reducers/restrictors already installed on the inlet to the boiler, that allows them to obtain their MI stated flow rates without having to resort to additional equipment being added to the system.

If I remember rightly, the ECO RF 24 specifically has a 8L restrictor installed to allow it to achieve it's output @ 35deg rise, if an output greater than that is required then it needs to be removed. Should be in the MI.

 

[Agile]

So many boilers do not put what you need to know in their MI.

When I started working on a Biasi 24S it made me panic when the heating would not come on after I had changed the gas valve.

Of course it was only the anti cycle delay but I instinctively expect that to be after it has been firing and not before!

 

[ianmcd]

Some boilers already have flow reducers/restrictors already installed on the inlet to the boiler, that allows them to obtain their MI stated flow rates without having to resort to additional equipment being added to the system.

If I remember rightly, the ECO RF 24 specifically has a 8L restrictor installed to allow it to achieve it's output @ 35deg rise, if an output greater than that is required then it needs to be removed. Should be in the MI.

yes many boilers have restrictors fitted, in Scotland we have areas with very high Flourine content, this causes the restrictors O ring to swell up and you have to remove it and manually set the flow rate with the cold water isolation valve

 

[boolie]

I checked my flow rate and I got 14ltrs in 30 seconds, so 24ltrs per minute.
Where are the maths police when you need them

 

[sxturbo]

I checked my flow rate and I got 14ltrs in 30 seconds, so 24ltrs per minute.
Where are the maths police when you need them

ha ha, typo

 

[transam]

combi out put X 14.2

divide figure by what ever temp rise u want = flow rate at that temp rise ( litres a min)

general temp rise used = 35 degs c