boiler size??

[stokecity]

hey guys,

i have calculated rad sizes, how many KW do u add on for hot water when sizing the boiler??

thanks

 

[SimonJohns]

Have a look at the cylinder. It will have a optimal kw for quick recovery

Other wise i add 3kw

 

[stokecity]

cheers mate, what about for combi?

 

[mountainman]

You add nothing for a combi as the boiler is already sized for hot water delivery.

 

[stevetheplumber]

combi is different smallest combis are 24kw most houses will be nowhere near, this for rad output but you size them purely on the hot water output
personally for the cost difference id fit nothing smaller than 28kw 30kw being the norm for one bathroom and a cloakroom house

 

[SafeGasInstall]

i am with steve on the combi ,winter comes and small combi can not heat mains quick enough , customers ring water is not hot enough specially when boilers are ageing

 

[AWheating]

for hot water cylinders its best to consult MI. Normally you would add 3kw but many cylinder now have fast/hi recovery coils that need far more especially unvented cylinders.

as mentioned a combi is sized on hot water demand.

 

[bengasman]

i have calculated rad sizes, how many KW do u add on for hot water when sizing the boiler??

None. Adding an x amount for dhw stems from the sixties; the practice has been obsolete since the arrival of independent timers.
However, I'd leave the calculation of the required capacity to the rgi that will install the boiler.

 

[jtsplumbing]

what size boiler do you have now ? or is this a new install with new rads ?

 

[fuzzy]

cheers mate, what about for combi?

doesnt matter for a combi, its either hot water or ch so doesnt run both at same time

youll find requirement for hw will be way more than ch

 

[stevetheplumber]

None. Adding an x amount for dhw stems from the sixties; the practice has been obsolete since the arrival of independent timers.
However, I'd leave the calculation of the required capacity to the rgi that will install the boiler.

cant see how the cylinder heat demand can be ignored regardless of the type system controls
especially now we demand so much hot water in anything other than the most basic of dwellings
a 210 litre unvented cylinder needs 30kw of heat input to get a 19 min recovery time
extreme scenario i know but needs to be allowed for

 

[mountainman]

Guy was originally fitting a combi, no hws required!

 

[bengasman]

cant see how the cylinder heat demand can be ignored regardless of the type system controls ...

Very simple.
The only programmers allowed under the latest version of part L, are independent timers. As such, you get 100% of the boiler capacity heating up the cylinder; which is by definition more than any percentage added to ch. This is of course under the proviso that whoever programs the thing actually has the brains to read the manual and understand what it says.

 

[doitmyself]

The only programmers allowed under the latest version of part L, are independent timers. As such, you get 100% of the boiler capacity heating up the cylinder

You are assuming that "independent timers" means that the CH and HW are not allowed to be on at the same time.

 

[bengasman]

You are assuming that "independent timers" means that the CH and HW are not allowed to be on at the same time.

Not quite.
If anything, I'd assume that a rgi actually has arrived in the 21st century, and has enough insight not to WANT them on at the same time.

 

[dancinplumba]

Not quite.
If anything, I'd assume that a rgi actually has arrived in the 21st century, and has enough insight not to WANT them on at the same time.

rgi ? its the homeowner, nowt to do with rgi
imo

 

[bengasman]

rgi ? its the homeowner, nowt to do with rgi
imo

I would hope that the programmer is installed by a pro and that he has enough quality to enquire about the customer's wants/needs and then set it up accordingly with the warning afterward that any change without completely understanding of the process is bound to cause significant performance reduction and/or bill increase.
If a homeowner wants to go on the cheap and do the job without understanding how it should be done, he gets what he pays for.

 

[doitmyself]

I would hope that the programmer is installed by a pro and that he has enough quality to enquire about the customer's wants/needs and then set it up accordingly with the warning afterwards that any change without completely understanding of the process is bound to cause significant performance reduction and/or bill increase.

So every time the customers hot water requirements change, he is expected to call the installer and ask him to come in and "reprogramme" the system so it is still working at maximum efficiency?

Presumably you install programmers which do not have "boost" or "extra hour" buttons on them.

 

[dancinplumba]

I would hope that the programmer is installed by a pro and that he has enough quality to enquire about the customer's wants/needs and then set it up accordingly with the warning afterward that any change without completely understanding of the process is bound to cause significant performance reduction and/or bill increase.
If a homeowner wants to go on the cheap and do the job without understanding how it should be done, he gets what he pays for.

and why would you not want them on at the same time ? please enlighten a professional

 

[bengasman]

and why would you not want them on at the same time ? please enlighten a professional

A pro? As in registered gas installer?
If so, I suggest you read up on developments in controls that have taken place since the previous century. Apart from that, it is blatantly obvious, AND I've already explained it above; if you still don't get it, I'm afraid it will be beyond my educational skills to help the penny drop.

 

[dancinplumba]

A pro? As in registered gas installer?
If so, I suggest you read up on developments in controls that have taken place since the previous century. Apart from that, it is blatantly obvious, AND I've already explained it above; if you still don't get it, I'm afraid it will be beyond my educational skills to help the penny drop.

clearly

 

[Puddle]

Please keep thread on topic and away from any personal remarks
thank you

 

[dancinplumba]

and why would you not want them on at the same time ? please enlighten a professional

? need to go and have a shower so i will go and put my hot water and heating on (oops both at the same time )

 

[ecowarm]

Not quite.
If anything, I'd assume that a rgi actually has arrived in the 21st century, and has enough insight not to WANT them on at the same time.

Bengasman, the type of system for what you're describing would be a Honeywell "W" Plan, hot water priority, the custommer could alter the program how they like, i.e. have heating + HW on 24hrs or all day or any other setting they like, but the HW would get 100% of the boiler output to recharge the cylinder. Without the need to worry if they messed up the times.