Boiler Condensing/Balancing Questions/Theory

[David A]

Hi all,

I have read through numerous online guides as well as the pinned Balancing Radiators Thread on this forum. However still have several questions.

Earlier this year we moved to a bigger house and with the rising energy costs just want to ensure we are doing our best to get the most efficiency out of our heating system as I'm sure everyone is. We have a combi condensing boiler. Unfamiliar with many terms so forgive me if I am getting things confused.

Firstly in regards to the boiler condensing and the flow and return temperatures.

• Is the goal essentially the ability to set the flow temperature low enough whilst ensuring radiators give off enough heat to still heat the room to a comfortable level? This would result in a saving as for example heating the flow to 80 degrees as opposed to 50 degrees would take slightly longer/make the pump work more often?
• How does the return temperature come into play/how relevant is it for condensing?
• Are there any optimal ratios as guides?
• How can one practical verify the temperature of the flow and return?

Secondly does the above for condensing what the flow/return is set to impact the radiator balancing.
- I.e. if flow is set to 80 degrees or 50 degrees, would the recommended value drop between the radiator lockshield and TRV (if fit) change? So instead of being 12 degree difference be something else?

Appreciate any responses. Thanks.

 

[Chuck]

The return temperature at the boiler governs the temperature of the heat exchanger surface that condenses the water vapour component of the products of combustion. The lower the better for this but there is a law of diminishing returns so 50°C is the usual target for a natural gas boiler. There is a circa 10% gain in 'efficiency' (i.e. reduction in fuel consumption) to be had by reducing the return temperature from 60°C or above to 50°C or below.

Living areas are most comfortable when the radiators are on continuously with a flow temperature that is just right to balance the losses from the room. Weather compensation attempts to achieve this.

When weather compensation is not available, the boiler flow temperature is set to a fixed value, typically 65°C and the boiler cycles on and off so the average power delivered to the house satisfies a thermostat that is positioned near the centre of the dwelling.

You can measure the flow and return temperatures with 'pipe thermometers' which you can buy anywhere that sell heating components. Alternatively, you can put your thumb on the pipe and time how long you can keep it there before you go 'ouch' and take it off. If that's ten seconds or more the pipe is at around 50°C or below. Zero seconds and it's around 60°C or above. This assumes that you have a British Standard thumb, of course.