Pump sizing help (domestic)

[matt73]

PUMP SIZING.
2 boilers max 50kw
1 250l unvented
23-25 rads totalling around 40kw
Low loss header
Distribution header

This is what we are going with. We are hoping to try to zone off what we can onto separate rf stats linked to zone valves. But as all piping is concealed and under floors this may prove difficult.
I can’t calculate index circuit so what advice can be offered re pump sizing? It’s a 2 storey property with 2 rads in loft also. Pump to be sited ground floor. I’m guessing a single 15/60 won’t be upto it but didn’t want to over spec a pump.
thanks in advance for any advice

 

[ShaunCorbs]

If your going one main one 25-80 will do it fine

Separates 15-60 will be fine

Header needs to be 42mm tho

 

[matt73]

If your going one main one 25-80 will do it fine

Separates 15-60 will be fine

Header needs to be 42mm tho

just to clarify,
if Im just going to tag onto existing flow and return and see what happens (1 big zone) then 25-80.
if I'm able to zone off into 3-5 zones then 15-60?

do you mean distribution header or low loss header? I got my calc at 35mm? wondering now if I've made a mistake on the header??

 

[ShaunCorbs]

Correct pump just after the llh/plate on commons/ header 25-80

Each leg/zone 15-60

And 35mm is pushing it for 5 zones when there all pulling prob just scrap it but I wouldn’t

 

[matt73]

Correct pump just after the llh/plate on commons/ header 25-80

Each leg/zone 15-60

And 35mm is pushing it for 5 zones when there all pulling prob just scrap it but I wouldn’t

You’re right. I can easily upsize to 42mm. So will do this.
If I only had 3 zones do you think 35mm ok? It’s so difficult to gauge without seeing any pipes existing.

I guessing one 25/80 is the way to go instead of 4-5 15/60’s. Far cheaper option ?
Thanks for your advice it’s very useful

 

[ShaunCorbs]

Yes 3 zones would be ok on 35mm but always better to slightly oversize

That decision is upto you

 

[Last Plumber]

Is there a reason you cannot calculate the pipe sizes and index circuit losses?
I am not saying the plan you have won't work but it is always better to 'know' what you're doing will work before you do it.

 

[Brambles]

If you don’t properly calculate and design a system of that size, you will be disappointed with the performance of the final installation.

I have seen it so many times - normally noise and the radiator that never heats up properly!

 

[matt73]

Is there a reason you cannot calculate the pipe sizes and index circuit losses?
I am not saying the plan you have won't work but it is always better to 'know' what you're doing will work before you do it.

all existing pipework is concealed under inaccessible flooring and ceilings. The longest run I've found is in 28mm running 4 x double rads approx 7kw rads with the furtherest rad on that circuit about 17m away. This appears the longest single run. Cant identify fittings and its just guesswork on the exact distance. Im happy I've sized boilers etc correctly just not sure on the pump. I wanted one single pump after the header and before distribution header but just not sure on size. any advice?? thanks

 

[Last Plumber]

all existing pipework is concealed under inaccessible flooring and ceilings. The longest run I've found is in 28mm running 4 x double rads approx 7kw rads with the furtherest rad on that circuit about 17m away. This appears the longest single run. Cant identify fittings and its just guesswork on the exact distance. Im happy I've sized boilers etc correctly just not sure on the pump. I wanted one single pump after the header and before distribution header but just not sure on size. any advice?? thanks

If you can't see it then it is difficult.

The index circuit is not necessarily the 'longest' run.

I really don't know what advice I can give to be honest as I haven't seen it.

If you use a large pump like the one mentioned and zone off as you have drawn, I would expect issues with noise amongst other future problems and complaints.

It is probably better, if guess work is all that is available, to use 15-60 modulating pumps on each circuit but only you know through experience and having been to site, what the set up is.

You must be able to calculate the flow rates required for each zone as you can see the emitters?
Going off that, work out the pipe size which 'should' have been used. In turn those figures will give you the initial pipe size required from the header.

I don't know if this helps any?

 

[ShaunCorbs]

If you can't see it then it is difficult.

The index circuit is not necessarily the 'longest' run.

I really don't know what advice I can give to be honest as I haven't seen it.

If you use a large pump like the one mentioned and zone off as you have drawn, I would expect issues with noise amongst other future problems and complaints.

It is probably better, if guess work is all that is available, to use 15-60 modulating pumps on each circuit but only you know through experience and having been to site, what the set up is.

You must be able to calculate the flow rates required for each zone as you can see the emitters?
Going off that, work out the pipe size which 'should' have been used. In turn those figures will give you the initial pipe size required from the header.

I don't know if this helps any?

25-80 ups2 is self modulating so won’t run at full speed when it senses a small circuit / not much resistance

 

[Last Plumber]

25-80 ups2 is self modulating so won’t run at full speed when it senses a small circuit / not much resistance

I know that Shaun.

We don't know the circuits though do we and even modulating pumps have a minimum performance. If he is guessing, it is better to try and avoid over-sizing as well as under-sizing something. Very difficult. I like to 'know' what the outcome will be rather than guess. If you have a very small circuit on a pump which is over sized, you will have issues.

This isn't the way I would do it and I was only trying to offer some advice based on the small amount of information I have.

Whilst on the subject of pipe sizes, the figures you posted elsewhere but to the same OP as a rough guide, seem high to me. Where are they from?

15mm 20kw
22mm 40kw
28mm 70kw

 

[ShaunCorbs]

I know that Shaun.

We don't know the circuits though do we and even modulating pumps have a minimum performance. If he is guessing, it is better to try and avoid over-sizing as well as under-sizing something. Very difficult. I like to 'know' what the outcome will be rather than guess. If you have a very small circuit on a pump which is over sized, you will have issues.

This isn't the way I would do it and I was only trying to offer some advice based on the small amount of information I have.

Whilst on the subject of pipe sizes, the figures you posted elsewhere but to the same OP as a rough guide, seem high to me. Where are they from?

15mm 20kw
22mm 40kw
28mm 70kw

True but as he said he can’t and tbh most people don’t size them on a standard system anyway

I normally size them off the number of rads and rough layout

Bs copper spec

 

[centralheatking]

I know that Shaun.

We don't know the circuits though do we and even modulating pumps have a minimum performance. If he is guessing, it is better to try and avoid over-sizing as well as under-sizing something. Very difficult. I like to 'know' what the outcome will be rather than guess. If you have a very small circuit on a pump which is over sized, you will have issues.

This isn't the way I would do it and I was only trying to offer some advice based on the small amount of information I have.

Whilst on the subject of pipe sizes, the figures you posted elsewhere but to the same OP as a rough guide, seem high to me. Where are they from?

15mm 20kw
22mm 40kw
28mm 70kw

In my last house I tried 2x 7 or 8 kw rads on a single drop 15 mm flow and return circuit
the performance was poor, it was ok as the 2 were back to back with one in a conservatory and the conservatory one I left off or slighty on but would not do it again or for a customer...that house was demolished
so nobody got landed with it....have a good weekend...centralheatking

 

[Last Plumber]

Bs copper spec

You need to look again at that information again Shaun, if you want my advice.
You won't achieve those outputs from those pipe sizes on a Heating system.

 

[ShaunCorbs]

You need to look again at that information again Shaun, if you want my advice.
You won't achieve those outputs from those pipe sizes on a Heating system.

Post your information up it’s not classified

 

[Last Plumber]

In my last house I tried 2x 7 or 8 kw rads on a single drop 15 mm flow and return circuit
the performance was poor, it was ok as the 2 were back to back with one in a conservatory and the conservatory one I left off or slighty on but would not do it again or for a customer...that house was demolished
so nobody got landed with it....have a good weekend...centralheatking

It would be very poor! Obviously it depends on route, run, outputs required, delta T, amongst other things but you would be pushed to get much more than 25000 Btu/hr out of 15 mm copper tube in my experience. I certainly wouldn't attempt much over that.
[automerge]1572013780[/automerge]

Post your information up it’s not classified

What does that mean? post your information up it's not classified?

 

[ShaunCorbs]

It would be very poor! Obviously it depends on route, run, outputs required, delta T, amongst other things but you would be pushed to get much more than 25000 Btu/hr out of 15 mm copper tube in my experience. I certainly wouldn't attempt much over that.
[automerge]1572013780[/automerge]

What does that mean? post your information up it's not classified?

Your figures mate

Mine are here

https://copperplumbing.org.uk/sites/default/files/content_attachments/small-bore-heating-systems_1.pdf

 

[Last Plumber]

If you look at those figure Shaun, you will see what I say is correct!

15 mm will give you 2 -10 Kw output on an 11 degree drop across a system. They have given a max of 1.5M/s which is something I personally would stay away from due to noise but that is my preference of course.

If you stick to a drop of 11 deg and a max of 1 M/s you'll avoid noise and the figures I mention to @centralheatking were right at around 7 Kw for 15 mm, dependent on run.

I can see looking at that chart you just posted, that if you took it to 20 deg difference and pushed it to 1.5M/s you will get close to the figures you posted so I can see where you get that from now.

I don't agree with doing it though. Maybe I'm old fashioned but it works for me to stick to the methods I use and know to work well.

 

[matt73]

If you don’t properly calculate and design a system of that size, you will be disappointed with the performance of the final installation.

I have seen it so many times - normally noise and the radiator that never heats up properly!

Heat loss, boiler sizing, pipe sizing to distribution header all calculated. Th only thing I’ve not is the pump due to all concealed piping (existing). I’m zoning what I can but just needed advice on pump
Thanks
[automerge]1572077780[/automerge]

I know that Shaun.

We don't know the circuits though do we and even modulating pumps have a minimum performance. If he is guessing, it is better to try and avoid over-sizing as well as under-sizing something. Very difficult. I like to 'know' what the outcome will be rather than guess. If you have a very small circuit on a pump which is over sized, you will have issues.

This isn't the way I would do it and I was only trying to offer some advice based on the small amount of information I have.

Whilst on the subject of pipe sizes, the figures you posted elsewhere but to the same OP as a rough guide, seem high to me. Where are they from?

15mm 20kw
22mm 40kw
28mm 70kw

Thanks for your info. Like I said there’s 21 plus rads inc unvented cylinder and some very long runs of pipes in 22. Some of the 22 legs running 16 plus metres flow with 4 rads each about 1.5 - 2kw rads.
I’m fitting the IMI trvs with inbuilt flow setting. So I size the rad off their app and set the trv internal setting to a number which corresponds to the required flow rate of that rad. I’m hoping this helps settle things. I’ve tried as much as possible to size everything.
like the drawing shows I’ve got 2 boilers 18-25kw
Both 22mm cascading into 28mm. Running about 6m to a LLH (sized correctly) then to the pump(not known which yet) then to 42mm header with 3 zones.
so is the consensus to use separate 15/60 on the zones or one main pump after LLH?
the below image shows day one. Note the distribution header is positioned on this photo is to be sited to the right of where it is now. The pump will fit in this gap.