Radiator Sizing for 40c Vogue condensing boiler

[markdu]

Hi there,

We had a new combi boiler installed and decided to change the radiators at the same time. I went on to numerous websites calculating the appropriate Btu's and sent these to the plumber who agreed they were correct and stated he would base the radiators on these calculations.

We have noticed that the house was colder and struggled to get to 18 degrees even after the heating has been on for over 5 hours.

The radiators were very hot to the touch and the boiler temp is turned up to maximum.

I therefore checked the radiators (prorad) and noted that the BTU output quoted was a lot lower that agreed with the Plumber. The plumber has stated that the radiators do meet the BTU outputs according to his chart. I have yet to see this.

I based my figures on the European standard of delta T50. The only way I can see that he could get anyway near the required BTUs is to work off a delta T70.

Am I correct in working off Delta T50 to correctly size the radiators.

many thanks for you help

 

[oz-plumber]

You are correct in sizing the radiators to delta t 50.

A delta t of 70 would be near impossible to achieve on any system.
( and have your home heated to 20 C )

 

[gmartine]

Sounds like your plumber just went along with your suggestions without checking or this is a DIY job gone awry.

Rads are either undersized or not balanced, the problem with many online heat loss calculators is they only take into account heat loss room per room rather than the building as a whole therefore no account is taken of say pipe losses. Rad manufacturers also test in perfect conditions much like car manufacturers do when quoting mpg therefore add 25% to the output requirement of each rad.

 

[newcastle phill]

Youve gone wrong way with delta t. You should be calculating nearer D40 for a modern boiler.
I think rads are undersized.

 

[Roger Welton]

Agree with phil delta T 40 for condensing boiler 70/50 F/R = MWT 60degC and 20deg room temp = 40deg deltaT

 

[Rickster123]

Can you list a few room sizes and rad sizes, noting how many outside walls etc? Just so that we can get an idea of sizes?

 

[markdu]

House is edwardian so solid walls and high ceilings and about 50mm of old blown in insulation in loft.

Dining Room ​3.366m X 3.631m​ ​800x600 type 22 (2 outside walls)
Lounge ​3.974m X 4.376m​ 1100x600 type 22 (2outside walls)

Bedroom ​2.032m X 2.692m​​ 600x600 type 11 (1 outside wall)
Master Bedroom 4.389m X 3.311m​​ 1100 x600 type 21 (2 outside walls)
Guest bedroom ​3.649m X 3.348m 1000x600 type 21 ( 2 outside walls)

 

[quality]

they are looking a good bit undersized there are varying outputs between manufacturers but not by the amount that at least 2 of your radiators out

 

[Worcester]

House is edwardian so solid walls and high ceilings and about 50mm of old blown in insulation in loft.

Dining Room ​3.366m X 3.631m​ ​800x600 type 22 (2 outside walls)
Lounge ​3.974m X 4.376m​ 1100x600 type 22 (2outside walls)

Bedroom ​2.032m X 2.692m​​ 600x600 type 11 (1 outside wall)
Master Bedroom 4.389m X 3.311m​​ 1100 x600 type 21 (2 outside walls)
Guest bedroom ​3.649m X 3.348m 1000x600 type 21 ( 2 outside walls)

Sound way undersized, without doing proper heat loss calcs, typically you'd be looking anywhere from 150-200w/m2 (despite being older than most of you guys on here I don't deal in BTUs'hr )

So Master Bedroom = 2.2kW with a condensing boiler on a DeltaT 40 assuming also factor for bottom connections, rad size should be: 40% larger than a Delta T 50, so you need a 600 x 2400 Type 21, or a 600 x1800 Type 22

You're probably about 100% undersized ... (they need to be twice as large..)

 

[Worcester]

We're just working on a 14th Century Solid (Brick/timber) property, 2 up 4 down, heat load is 16kW = 170W/m2 average.

So: master bedroom 3 outside walls, which is at 185w/m2 (4.3m x 4.5m) = 3580 needed a 600 x 1600 K3 / Type 33, output = 3822W
We had to put feet / floor mounts on it else it would have fallen off the wall

We're using a biomass boiler, so DeltaT=50 is fine



Plumber vs Heating Engineer .... nuff said, expensive mistake, the house will never get warm.

 

[Simon F]

all that said. try to get the insulation improved.
the loft is usually done free!