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]

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)