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 ☺️.

 

[SJB060685]

If they're off grid why not consider an oil boiler?

 

[Chester]

If they're off grid why not consider an oil boiler?

They're in the centre of a town

 

[SJB060685]

They're in the centre of a town

Oh, haha, my bad. Having said that we did use to have an elderly customer on oil in the town. He refused to switch over to gas lol.

 

[king of pipes]

If they're off grid why not consider an oil boiler?

Their not bud just don't want gas because they think it's polluting and harmful to the environment should watch seaspiracey on netflix see the harm countries are man are doing sickening. Kop

 

[Chester]

Oh, haha, my bad. Having said that we did use to have an elderly customer on oil in the town. He refused to switch over to gas lol.

its a combi job all day long, I know that, but I'm just following orders, I will quote them for unvented and heat only electric and see what they want to do

 

[IND_Nick]

I had a similar customer, who had done online research and thought electric would be a great idea to future proof the house. However once I went through the cost of install, running and the fact that most electric units are only carry a 2/3 year warranty he soon agreed to a replacement gas boiler.

 

[cjg]

just one more point do they cook on gas or leccy, power cut no heating or cooking.
yes i know ,,, no leccy no heating even if you use gas, but!!!!
thats my pennys worth now,..

 

[Chester]

just one more point do they cook on gas or leccy, power cut no heating or cooking.
yes i know ,,, no leccy no heating even if you use gas, but!!!!
thats my pennys worth now,..

no gas hob just the boiler

 

[Ben-gee]

Consider the personality of the customer, this job would be ringing alarm bells for me - remember sometimes a job is not worth doing from your point of view and it’s best to walk away.
If it’s a job you’d not wish your name to be associated with, for example when they start telling people that their bills have gone mad since you fitted the new boiler etc - just don’t do it.

 

[king of pipes]

Personally I don't think the power supply will be adequate for heating, hotwater, cooking , a kettle, computers TVs , gaming and to top that probably a charging point for a car or two if not now then in the future, I'd be getting a calculation done allowing for a -2- 3 degree temperature outside for a week or two and all these appliances loading it will be a mind blowing and a game changers I guarantee, take some Viessman boiler information with you these are designed for the changes coming to the Natural gas supply, the future is Hydrogen Natural gas mix the co2 produced from the combustion process is vastly reduced it's being trialled and tested in parts of the UK now that the future and the way I would be pushing this customer is this direction , or saying sorry I'm out . Kop

 

[king of pipes]

Maybe Murdoch should come in on this one ?? He knows his stuff on Electrics

 

[Chester]

Maybe Murdoch should come in on this one ?? He knows his stuff on Electrics

it'll be fine, its only 12kw, they have a 100amp supply, boiler has soft start and is modulating too which is nice.

 

[king of pipes]

it'll be fine, its only 12kw, they have a 100amp supply, boiler has soft start and is modulating too which is nice.

What you installing bud ??

 

[Chester]

What you installing bud ??

Potterton Gold electric

 

[king of pipes]

Only a years warranty and a D sebuk rating , I wish you well with it bud but alarm bells are ringing for me anyway. All the best kop

 

[ShaunCorbs]

Same as a slim Jim good units

 

[SJB060685]

Although I know quite a bit on electricity I'm by no means a qualified electrician. Is a 100 amp supply really going to be enough for a 12 kw boiler at full load and all other appliances running?

 

[ShaunCorbs]

Although I know quite a bit on electricity I'm by no means a qualified electrician. Is a 100 amp supply really going to be enough for a 12 kw boiler at full load and all other appliances running?

yes easily 12kw is 50amps provided he doesn’t run a big 20 plus amp cooker at the same time

also 12 kw is max load when the system warms up this could drop to around 6kw

 

[SJB060685]

yes easily 12kw is 50amps provided he doesn’t run a big 20 plus amp cooker at the same time

also 12 kw is max load when the system warms up this could drop to around 6kw

That's my point mate. Yes the boiler will modulate but what when it's -2°c outside, the boiler is at full output and then you switch on an electric cooker, plus your 1 or 2 32 amp ring mains and your lighting circuits etc etc. Admittedly this is an extreme situation scenario but like heating systems shouldn't all electrical systems be designed with max load in consideration?

 

[Ben-gee]

Actually no, they are not designed at maximum load - diversification is applied, don’t forget most heating elements actually cycle off/on to maintain a given temperature and pretty much anything that is not a heating element does not draw much current.
I’m over simplifying, but you get my drift.

 

[SJB060685]

Actually no, they are not designed at maximum load - diversification is applied, don’t forget most heating elements actually cycle off/on to maintain a given temperature and pretty much anything that is not a heating element does not draw much current.
I’m over simplifying, but you get my drift.

Thanks buddy. Yes I totally understand you and to be honest it's not something I knew. Many thanks 🙏.

 

[Chester]

Only a years warranty and a D sebuk rating , I wish you well with it bud but alarm bells are ringing for me anyway. All the best kop

Cheers, I spoke with them again today and laid it all out for them on the table, the potential bills from gas being 4 to 5x cheaper and whilst they were like yeah okay that's cool.. they still want electric. Honestly what more can I do? They don't want a gas boiler, period. There is no alternative. They asked what I would do, I said gas all day long, combi boiler, and bring gas in to cook on too. They're not interested, I think it also matters that these people are quite wealthy so the allure of saving money doesn't really grip them as much. What I'm going to do is arrange the system so in the event of a backfire (which I don't think will happen) I can just put a heat only gas boiler in with ease, I'm all out of ideas bar turning the job down.

 

[king of pipes]

Actually no, they are not designed at maximum load - diversification is applied, don’t forget most heating elements actually cycle off/on to maintain a given temperature and pretty much anything that is not a heating element does not draw much current.
I’m over simplifying, but you get my drift.

Agreed Ben- gee its the diversity factor if you take the full current loading of all the breakers in the fused board it could be way higher than 100 amps but each of of these circuits will not all be at full load so diversity is applied .

 

[ShaunCorbs]

That's my point mate. Yes the boiler will modulate but what when it's -2°c outside, the boiler is at full output and then you switch on an electric cooker, plus your 1 or 2 32 amp ring mains and your lighting circuits etc etc. Admittedly this is an extreme situation scenario but like heating systems shouldn't all electrical systems be designed with max load in consideration?

same as any normal house as

45 amps for a electric shower
32 amp ring
20 amp kitchen
32 amp cooker

you will find a normal house will run at 20-25 amps at peak

 

[king of pipes]

Same as a slim Jim good units

Here's one installed but as said very expensive to run did the job on a off grid holiday home added a nest for smart control on the heating side left the hot water on a Honeywell programmer

 

[Chester]

Here's one installed but as said very expensive to run did the job on a off grid holiday home added a nest for smart control on the heating side left the hot water on a Honeywell programmer

Lovely mate, pre plumb stelflow, I'm going to go pre plumb aswell the time saved is worth the extra 80 quid or whatever in my humble opinion

 

[Timmy D]

Have they got space in the consumer unit for another breaker?

Who’s running the electric?
Are you competent?
Potential extra cost?
Is there a route for the new supply?
Depending on the route, you could be looking at a 16mm cable.

 

[Chester]

Have they got space in the consumer unit for another breaker?

Who’s running the electric?
Are you competent?
Potential extra cost?
Is there a route for the new supply?
Depending on the route, you could be looking at a 16mm cable.

Electrician
yes
yes
consumer unit in the same room as boiler

 

[cjg]

ps. don"t forget plug the electric car in to charge (lol)