Boiler sizing

[cully]

Am I on the right lines with my thinking or am I missing something?
If the total heating kW required in a house is calculated at 30kW and the DHW heating requirement is 25kW then a CH boiler sized at 35kW would suffice?
(during the time that the DHW was calling for heat say 30 min. there should be no issue with CH temp. drop over this period as the system is predominantly UFH)?????

 

[Dan Robinson]

30kW of UFH? How big is the house and how did you get to 30kW.

Do you know what the 25kW hot water requirement is?

 

[Phill Peck]

My guess is coil rating.

 

[Dan Robinson]

 

[cully]

Dan, the 30kW UFH requirement came from the suppliers "UFH1" that calculated the heating requirement for the ground floor (300 sq. mtr)
The 26kW for DHW was a calculation for a 300l cyl giving a recovery time of around 45min.
What I am asking is whether the principal is correct as my house is similar to above but not as big. The DHW has priority over the heating and there is no drop in temp in any room (incl. rads on the first floor) whilst the boiler is servicing the DHW

 

[Agile]

I am happy with that calculation because the UFH equates to 100 W per sq m which is a typical UFH power output. Well insulated homes don't need that much output but more aids faster heatup.

The taught standard addition for HW is just 2 kW although some installers dont like to accept that and like to add more.

The logic being that the full CH power is only needed when it is -1 C outside.

Also the HW reheat can be timed outside the main heating times so that the whole boiler power is available.

Tony

 

[Dan Robinson]

100 W per sq m which is a typical UFH power output.

Really?

 

[Steelmasons]

The taught standard addition for HW is just 2 kW although some installers dont like to accept that and like to add more.

The logic being that the full CH power is only needed when it is -1 C outside.

Also the HW reheat can be timed outside the main heating times so that the whole boiler power is available.

...and if the building heat loss were only 8 kW??....what size boiler would you recommend taking into account HW coil rating to be 25kw??

 

[Steelmasons]

The taught standard addition for HW is just 2 kW although some installers dont like to accept that and like to add more.

Taught by who?...I don't recall being taught this when serving a 7 year City & Guilds apprenticeship in plumbing & heating?...
Tony , who did you serve your apprenticeship with and what college did you attend?

 

[Agile]

Taught by who?...I don't recall being taught this when serving a 7 year City & Guilds apprenticeship in plumbing & heating?...

It is taught on the Energy Efficiency course which all installers self certifying their work are meant to have completed.

I did mine about 2005 at Baxi in Warwick!

 

[Dan Robinson]

It is taught on the Energy Efficiency course

about 2005

And it was a load of bo!locks back then. I did mine in Bracknell donkeys years ago, and apparently again in 2006 - although I'm fecked if I can rmember where....

 

[Steelmasons]

It is taught on the Energy Efficiency course which all installers self certifying their work are meant to have completed.

I did mine about 2005 at Baxi in Warwick!

Is this the only training that you've received?..A one day course with no pass or fail?....The type of course a chimp could get his head around..
We've all attended this course at one time or another..

 

[PullerGas]

Is it the same as the Part L course? I did that yonks ago, complete cr.p!!

 

[cully]

Some interesting conversations above but what's the thoughts about my original thread?

 

[Dan Robinson]

Well assuming the heat loss calc is correct, then fine. Size the boiler to the largest single load. Although 30kW of UFH is massive. I mean massive for a regular house.