You mean mathematically?. if a differential head of 3M results in a flow of say 13 LPM (like my heating system) and I increase the (pump) head to say 5M, the resultant flow will be the original Flow X the sqroot of the (newhead/oldhead).....13X sqroot(5/3) = 13X1.29 = 16.77 LPM.
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Central heating pump sizing
Discuss Central heating pump sizing in the USA Plumbers Advice area at PlumbersForums.net
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Thanks buddy. That makes sense now
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Although they both have this part number DAB 60161174, the images look different......the Amazon one is more expensive Andries than even look like it has the data display.....
Will phone PSD tomorrow and confirm, think this is my best hope, seems a very good price £62.39 inc free postage....any thoughts ? 1st image PSD 2nd image Amazon
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That’s the one on the left, curious how prices vary, £60-£150.....eBayera are an optimistic breed
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Problem is, I have just been advised this is a 180mm length pump whereas mine is 130mm, is that correct ?
The DAB3 appears to be a 8M pump hence the 180mm between centers so I would advise against this as it involves piping mods and drain down, also 130mm centers gives you more choice of 6/7M pumps.
While the Wilo or Dab Evosta2 (no display) will almost certainly give you the required head/flow I think you are better off installing a pump like a Grundfos UPS3 15-50/65 which is very powerful 6.5M pump which will satisfy your needs with ease. For example it will pump 33LPM @ 4.5M, Dab2, 33LPM @ 3M and the Wilo 33LPM @ 3.2m.
Unfortunately, this UPS3 does not display watts but not the end of the world as you really only need this as an aid to see if you have a pump problem or a restriction. By spending a few extra bob you can buy a nice little plug in energy monitor, I have a few and they are quite accurate, (see link) and use it like this.
I assume you intend to clean the existing pump head so before removal/clean, remove the pump lead and fit a 3 pin plug. ensure boiler off and any zone valves if fitted, latched open, plug in the pump lead to the energy monitor in turn plugged in to any convenient socket or extension lead, note the watts, remove plug, clean pump head and ports, then re measure power.
Depending on findings, if you do decide to install the UPS3 or whatever, do likewise, stick a 3 pin plug on it and you can then monitor its power in its different operating modes and then run the pump on the appropriate setting. When tests complete re install pump lead to wiring center.
One word of caution if removing the pump by opening the isol valve nuts, these can be extremely difficult to undo, I have change out a few pumps for neighbors and one of my own and have always drained down and removed the pump complete with isol valves, I then found it quite difficult to remove the pump valves even though I obviously renewed them with the new pump.
PS: fairly sure your pump has 130mm centers but best to measure up.
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Thanks for all the advice, sounds like the way to go.....will investigate the power to my pump, looks rather complicated, as this also had its wiring modified.....when an electrician came round a few years ago, he made some changes, involved lifting up the floor board to get access o the connections ( my dam extension buile
der
) found he had used a light switch as a junction box, now the new junction box in the immersion cupboard, but looks complex.....will have a careful look, taking photos as I go....all good fun what’s the LPM of the DAB3 ? Do like the idea of the displays, womder how it displays the flow, ant be a calculation as it doesn’t know the Delta T, must be an integral flow meter 
I don’t suppose a replacement pump comes with new valves, assume would have to be bought separately my CH pump iso valves have no handles, never have, can these be bought separately ? Be so much easier to isolate
der
) found he had used a light switch as a junction box, now the new junction box in the immersion cupboard, but looks complex.....will have a careful look, taking photos as I go....all good fun what’s the LPM of the DAB3 ? Do like the idea of the displays, womder how it displays the flow, ant be a calculation as it doesn’t know the Delta T, must be an integral flow meter I don’t suppose a replacement pump comes with new valves, assume would have to be bought separately
my CH pump iso valves have no handles, never have, can these be bought separately ? Be so much easier to isolateYour old pump isolating valves are probably 1/4 turn ball valves that you shut with a screwdriver (slot) or a allen key, nothing sticks out, but unfortunately they almost always leak after operation, you can easily buy new ones with gate valves.
It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.
It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.
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have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.... some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage
so assume PSD is owned by Stuart plumbing.....must be offering competition to their own company.....marketing strategy 
the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term....P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner.....so much easier with a handle......maybe will replace them when I change the pump
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You have the correct type isol valves as the gland nut can be tightened up if any leak, so no need for renewal.have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.* some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage
P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner..so much easier with a handle...maybe will replace them when I change the pump
Would suggest constant pressure, either CP2 or CP3 see below, answer to SJB.
Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.
you will see that on constant pressure CP3 that the pump will maintain 4.8M from 0 flow, if the system demand is 1 m3/hr 16.7 lpm then the pump power is 35w, if a restriction in the system and the flow fell to zero then the power is 16.5w and so on in between. more later
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Which chart am I looking at?
Through common sense I imagine if there was a restriction on PP then the pump would modulate down and display a lower wattage?
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I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult......it’s not rocket science.....so we‘ll get thereThanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something
keep asking questions, it’s the only way to learn.....also when people understand something so well it’s sometimes easy to downplay an answer.....I will persevere, I want to understand this.....trouble is the pump I ordered has lots of options so need to understand that also, just hope the others are patient with me 
Page 25 shows two graphs the top one is the normal pump curves and I am just assuming that you have choosen the pump to run on setting CP3 and just suppose that your system will circulate 16.67 LPM at this setting of 4.8m. if you look vertically downwards you will see another graph of power vs flow for all the different pump settings, you have choosen CP3 and because the system is circulating at 16.67 LPM then the pump power required is 35W, if the system, say boiler Hx starts getting dirty/fouled then the pump speed will reduce to maintain this constant head of 4.8M and if it got completely blocked the pump will still maintain 4.8m but with no flow and still require 16.5W. If you had a smaller system in that even when spotelessely clean only circulates 8.3 LPM (0.5m3/hr) then you can see that the pump only requires ~ 25.5W at the constant pressure of 4.5M.Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something
If you take my system as a example which circulates ~ 15 LPM (0.9m3/hr) @ 3.5M.......I could set the pump to CP2 which is constant pressure at 3.8M, my system would then circulate 15.7 LPM (0.94 m3/hr) @ 3.8M.
with a power demand of 26W.
I woud suggest CP2 (3.8M)as a reasonable starting point, it can very quickly be changed especially with all the info that will be displayed on this pump.
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I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult...it’s not rocket science..so we‘ll get there
My background is oil fired appliances, thats all we were, burner technicians. The system side of things is not something we did much of, so this last year I've been studying and learning a lot of new things to better my understanding. I have a passion for learning and a desire to at least have a good understanding in all areas of heating systems. John here has taught me a few things that I didn't know before joining this forum and to be honest, when it comes to pumps he's probably one of the best on here.
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Hi
i can only relate to my experience in the oil industry ( Mobil Coryton refinery ) when the pump discharge was shut back ( or there was another restriction to flow ) on a centrifugal pump the Amps ( power ) would drop off, as the pump would just be stirring the liquid and not doing any real work......not sure if that’s applicable, but IMO should be....
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Thanks again John. I've checked everything against the charts and did the maths for your bottom paragraph and it all adds up. Thanks for taking the time
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Please do. I have a basic understanding i believe but I'm sure you'll teach me otherwise lol
Ok, at tremendous expense here are a few numbers/attachments based on my requirements of 15 LPM @ 3.5M head and also based on the TRVs closing down with flow demand as low as 5 LPM.
speed2 will give 16 LPM@4M and 29.5W
speed2 will give 5 [email protected] and 27.5W
CP2 will give 15.9 [email protected] and 26W
CP2 will give 5 [email protected] and 17W
PP3 will give 16.8 [email protected] and 30W
PP3 will give 4.5 [email protected] and 12W
PP2 would almost do the job, [email protected] and (only) 12.2W.
speed2 will give 16 LPM@4M and 29.5W
speed2 will give 5 [email protected] and 27.5W
CP2 will give 15.9 [email protected] and 26W
CP2 will give 5 [email protected] and 17W
PP3 will give 16.8 [email protected] and 30W
PP3 will give 4.5 [email protected] and 12W
PP2 would almost do the job, [email protected] and (only) 12.2W.
CC or constant curve or fixed speed, the pump runs at a constant speed, the faster the speed the greater the head, all pumps have 3 CCs to cater for different size systems, the problem is the power consumption is almost constant because as the heating (flow) demand goes down due to zone vale closing or TRVs throttling in the pump head increases and the pump efficiency falls off as you can see by the tiny differences in the power consumptions between 15 LPM and 5 LPM.
CP or constant pressure is one of the best controls, the head stays constant due to the pump speed changing up/down to maintain the same head for different flowrates and gives big energy savings like above. 17W vs 26W.
PP or proportional pressure control can give the biggest savings of all as the pump (speed) and head decreases as the flow demand decreases, unfortunately because of the limited number of settings one sometimes has to select a higher setting than necessary like above, where PP2 falls just short of the required flowrate but only consumes 12W, the reason I choose the Wilo is that the PP settings can be incrementally changed in 0.1M stages to give any flowrate required.
Also PP control reduces the (speed) head as the flow decreases, and vica versa unlike the CC settings.
CP or constant pressure is one of the best controls, the head stays constant due to the pump speed changing up/down to maintain the same head for different flowrates and gives big energy savings like above. 17W vs 26W.
PP or proportional pressure control can give the biggest savings of all as the pump (speed) and head decreases as the flow demand decreases, unfortunately because of the limited number of settings one sometimes has to select a higher setting than necessary like above, where PP2 falls just short of the required flowrate but only consumes 12W, the reason I choose the Wilo is that the PP settings can be incrementally changed in 0.1M stages to give any flowrate required.
Also PP control reduces the (speed) head as the flow decreases, and vica versa unlike the CC settings.
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