Radiator F&R Temp Difference.

[Nicksun]

Morning all, I've drained and refilled my central heating system and have done a reasonable(imo) job of balancing the system. Other posts have said to check manufacturers recommendations for f&r pipe temps to the rads. I will be using an IR gun. My boiler is a Vaillant ecotec plus 428. Is the information below what I'm looking for as I can find no other mention of temp differential anywhere else.

3.14 Pump specification
The pump should be fitted on the flow pipe from the
boiler and have isolating valves each side.
A variable duty pump should be set to give a
temperature difference of no greater than 20°C

Cheers.

Nick.

 

[spudkey]

Yes a 20 deg differential is what you want it is also worth setting the max output of these boilers to match system. Add up the output of all rads and set boiler output to suit in menu d0

 

[Nicksun]

Cheers spudkey.

 

[Nicksun]

Hi spudkey, I went into d0 and it has a range of 5-30. It was set at 30 and I altered it to 21, I worked out my rad. outputs to approx. 19.5kw.
Is this ok?
Also, it's a sealed system of 12 rads. I've set the 3 speed pump to max. Would this be optimum?

Cheers.

Nick.

 

[D_Hailsham]

Hi spudkey, I went into d0 and it has a range of 5-30. It was set at 30 and I altered it to 21, I worked out my rad. outputs to approx. 19.5kw.
Is this ok?

21kW only gives 1.5kW available for the HW cylinder when the heating is running flat out. The minimum recommended is 2kW, so I would increase the boiler to 22kW.

You may have 19.5kW of rads, but that may not be correct for your house. Use the Whole House Boiler Size Calculator to find the correct size boiler for your house. Deduct 2kW for the answer to give the heating requirement.

The output of a radiator varies with temperature. If you balance the rads with a 20C difference (75C/55C instead of 75C/65C) the output is reduced by about 15% (a 1kW rad will only give off 850W).

You therefore need the rad total (19.5kW) to be about 20% more than the heating requirement if you want to balance at a 20C differential

Also, it's a sealed system of 12 rads. I've set the 3 speed pump to max. Would this be optimum?

Balancing at 20C means that the flow rate through the boiler is about half that for an 11C balance. The pump may only need to be on 2, or even 1 to give the correct balance.

Read How to balance a CH system.

 

[Agile]

An IR thermometer will not give a very useful indication of the temperatures.

A contact thermometer should always be used!

With a little practice its not that difficult to do it with your hands.

The 20 C diff is to increase boiler efficiency by making it condense more.

Your boiler is designed for 20 C diff. if a Vaillant condensing model. It will also give you the boiler flow/return temps on d40/d41.

The pump should always be on maximum setting with a Vaillant 400 series as they have a high flow resistance.

Your boiler is almost certainly seriously oversized. Set d0 to the whole house heating loss as caclulated. Rad outputs depend on several factors are are best estimated but not used for boiler settings unless greater than the whole house figures.

Tony

 

[Nicksun]

Thanks for your replies. things have really been hotting up and i've used the feel method. I'll definately turn the kw up on the boiler, although i probably over estimated the rad outputs a little.
The boiler is over sized but it's future proofing against my current and future plans.
I'll check out the whole house caculation.

Thanks again.

Nick.

 

[D_Hailsham]

i probably over estimated the rad outputs a little.

If they are modern flat steel rads, use the Stelrad Elite Catalogue to find the outputs.