Pump Sizing

[Chester]

Hey guys long time since I have posted here but know some of you know your salt. I've got a job in a townhouse and currently the boiler sits on the second floor of a three story but I'm moving it to the ground floor as per client request, problem is, its got ridiculously high ceilings, I'm going to double check but suspect at the very least top floor rads are 7 meters up.. so I'm concerned about a standard 15/60 or whatever being man enough, I've been looking at the 25/80 as a viable alternative but I'll be honest I really don't have a great deal of experience in pump sizing, I'm usually just whacking in combis and forgetting about it 🥴 so I keep hearing that it'll make the system noisy and all these horror stories, just wondering if anyone could give me some advice basically. Current system is 22mm flow + return, currently open vented, 10 rads overall, I'm going to seal it and putting in a 180l unvented indirect. Also, client is a bit of an eco warrior so they want me to put in electric, electric boiler needs 12lpm minimum according to Mi's. Cheers

 

[ShaunCorbs]

Can you seal it ?

 

[Chester]

Can you seal it ?

yeah i will be

 

[ShaunCorbs]

Should be fine with a 15-60 then

 

[Chester]

Should be fine with a 15-60 then

Okay thanks Shaun, any chance you could you explain why that is? I always thought the height mattered whether its sealed or not

 

[ShaunCorbs]

As it’s sealed and the return will equal out the flow so your pump won’t have to work as hard

with open vent it will hep but not as much

 

[Chester]

As it’s sealed and the return will equal out the flow so your pump won’t have to work as hard

with open vent it will hep but not as much

I see, so in theory the weight of the water coming back down the return contributes to the force of propelling it up. At what point would it be worth uprating the pump given this effect?

 

[ShaunCorbs]

When the internal resists exceeds the pump spec or you need more flow

 

[Chester]

When the internal resists exceeds the pump spec or you need more flow

nice one thanks, so if the 15/60 doesn't work here that means i have a badly designed heating system 😂

 

[ShaunCorbs]

Yep / not pipedsized correctly

 

[cjg]

but electric is not eco friendly, and to run c.h. off is going to cost them a pritty penny.

 

[Chester]

Yep / not pipedsized correctly

so, the pressure is on - I'm here all night gents

 

[Chester]

but electric is not eco friendly, and to run c.h. off is going to cost them a pritty penny.

I know, depends who your supplier is i guess, 12kw gonna run some fat bills in winter. I have explained this to them considering they have gas in house, i cant wrap my head around it.

 

[cjg]

gas is miles cheaper, even when on a course about heat pumps they had to admit gas is best.

 

[Chester]

gas is miles cheaper, even when on a course about heat pumps they had to admit gas is best.

yeah gas is like 4 times cheaper or something on average

 

[king of pipes]

Madness I've done several electric systems and they ain't cheap to run you need economy 18 and a super insulated property I certainly wouldn't advise fitting one if there is gas available you will treble their energy bill , pump wise ? dab are my go to pumps as below . Regards kop

 

[Chester]

Madness I've done several electric systems and they ain't cheap to run you need economy 18 and a super insulated property I certainly wouldn't advise fitting one if there is gas available you will treble their energy bill , pump wise ? dab are my go to pumps as below . Regards kop

it is madness, I turned the job down initially saying to get some quotes locally for a combi install, its cheaper etc but they came back and said "no, we want electric" I said okay, and here I am. Thanks for the recommendation you think ill need the 8m head? I tried dab pumps once, I don't really like the electrical connector block inside the cheaper range, I had a faulty one from new mileeees away once. Very annoying.

 

[SJB060685]

This may have already been said but the height of a building has no bearing on the pump size required. The system is already filled and the pumps are circulatory, not lifters. As long as the pump can supply the pressure for the flow rate required to overcome the index circuit and heat exchanger resistance then you're ok. Again height is nothing to do with it.

 

[Chester]

This may have already been said but the height of a building has no bearing on the pump size required. The system is already filled and the pumps are circulatory, not lifters. As long as the pump can supply the pressure for the flow rate required to overcome the index circuit and heat exchanger resistance then you're ok. Again height is nothing to do with it.

thanks for clearing that up, i wonder when i see insta photos of 2 magna 1's and a llh on a 5 bed house whether its overkill, now im starting to think yes, yes it is... that poor customers wallet.

 

[ShaunCorbs]

It’s more down to the flow

 

[SJB060685]

thanks for clearing that up, i wonder when i see insta photos of 2 magna 1's and a llh on a 5 bed house whether its overkill, now im starting to think yes, yes it is... that poor customers wallet.

LLH's or any other means of hydronic separation is used if
1. Pump internal to boiler can't supply the head to the entire circuit/circuits.
2. If the flow rates on the secondary side are more or less than that the boiler requires.

Some may disagree but as systems become increasingly modulation controlled then most systems out there will benefit/need some kind of separation. Although if this can be designed out at the designing stage it's better.

 

[king of pipes]

Not had a issue with any I've fitted had more problems with Grundfoss pumps as the guys have stated system design has alot to do with it , even a electric boiler manufacturer state in their literature that they should only be installed if not on a gas network and in smaller properties , you know it will all be your fault when it under performs and the bill goes through the roof, 12kw the supply for that needs careful consideration and may not be possible with the rest of the house.

 

[ShaunCorbs]

Not had a issue with any I've fitted had more problems with Grundfoss pumps as the guys have stated system design has alot to do with it , even a electric boiler manufacturer state in their literature that they should only be installed if not on a gas network and in smaller properties , you know it will all be your fault when it under performs and the bill goes through the roof View attachment 62183

have you used there pumps kop ?

 

[Chester]

Not had a issue with any I've fitted had more problems with Grundfoss pumps as the guys have stated system design has alot to do with it , even a electric boiler manufacturer state in their literature that they should only be installed if not on a gas network and in smaller properties , you know it will all be your fault when it under performs and the bill goes through the roof View attachment 62183

I have told them numerous times that it will be very expensive. I think I'm absolved to any blame at this point. 12kw should handle the rads no problem but yes the bill is going to be eye watering.

 

[king of pipes]

have you used there pumps kop ?

Yes mate no problems Stuart Turner have a good reputation ☺️.