Boiler sizing

[GrahamT]

Hi

I have a customer who is having problems with radiators in the top floor not heating up. I haven't been to the premises yet, but they seem to think they may have an undersized boiler.

They have a Vaillant ecotec plus 831, which I've looked up as having a CH max output of 24kW. They also tell me they have 14 rads (inc 2 towel rails) over three floors - they haven't given me rad sizes but say they are pretty standard mix of single & doubles (1000 - 1400 wide).

I'm going there next Friday potentially to balance the rads, but does this sound like a case of undersized boiler?

How much BTU ratings do you allow for pipework when sizing a boiler?

Any thoughts, much appreciated.


Graham

PS. they had it power flushed before the new boiler went in. And the system at the moment has been bled and up to pressure

 

[kevindgas]

rads require approx 70 - 80,000 btu boiler can deliver over 100,000 so is big enough unless rads are huge

check d.0 is set at 24 not lower

 

[Agile]

I thought the 831 would give over 24 kW on CH?

Anyway thats irrelevant as I expect the installed load is probably about 13 kW anyway.

The whole house loss is probably less anyway.

The boiler probably needs to be rated DOWNWARDS anyway. The first thing you should do is see what its set at !

Tony

 

[kevplumb]

cue mr hailsham and his magic wizard

 

[GrahamT]

Sorry guys, I'm not a boiler engineer so won't be able to check the rating (Are you talking about burner pressure?).
The output 24kW I got from the vaillant installation manual. There is a section that says at 40/30 degrees C the range is 9.4 - 26.

I don't understand d.0 or "rated downwards" means.

http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/839592_09.pdf

 

[D_Hailsham]

cue mr hailsham and his magic wizard

Your wish is my command.

The Boiler Sizing Wizard will tell you what size boiler you need to heat your house.

You need to deduct 2kW from the final result as it is intended for systems with HW cylinders, not combi boilers. Provided the result is above the minimum CH output of your boiler, you should be OK.

The maximum CH output of your boiler is 24kW. This can be reduced using the installer controls. You have to set the display to d.0 to read/adjust the max output (its explained in the manual). If you need much less than 24kW, it is advisable to set d.0 to just above your actual requirement.

 

[bengasman]

cue mr hailsham and his magic wizard

Your wish is my command.

The Boiler Sizing Wizard will tell you what size boiler you need to heat your house.

As per usual, it is rather unlikely that the custard will change the entire heating system based on some silly computer program. Besides that, the size of the boiler is not the problem here anyway.

You need to deduct 2kW from the final result as it is intended for systems with HW cylinders, not combi boilers. Provided the result is above the minimum CH output of your boiler, you should be OK.

That went out the window a loooong time ago with the arrival of 20 kW high recovery cylinders

The maximum CH output of your boiler is 24kW. This can be reduced using the installer controls. You have to set the display to d.0 to read/adjust the max output (its explained in the manual). If you need much less than 24kW, it is advisable to set d.0 to just above your actual requirement.

Which shows once again that you are just a householder with no understanding of the subject. If you had installed boilers as a RGI, which you obviously have not, you would have noticed 2 things:
1. The upstairs rads staying cold is not a matter of the boiler being slightly too small.

2. Lack of heating up is never solved by rating the boiler down.

 

[kevindgas]

to check d.0 on control panel (left hand side of fascia 2 dials &4 buttons)
press i and + together
the display will say d.0
press i it should now give a no. between 9 & 24 that is what it is set at currently.

 

[Agile]

2. Lack of heating up is never solved by rating the boiler down.

Actually it sometimes is when the boilers is so over rated it reaches the set flow temperature in a couple of minutes and then sits off for severminutes waiting to start again.

The energy efficiency advice is still to add 2 kW to the CH power for hot water.

Tony