Condensing boiler: balancing radiators. Update.

We have a new condensing boiler retro-fitted to our existing system: Baxi Solo He 15, 8 rads some with TRVs.

With the pump at its lowest setting, I set the flow to about 64 C and the return to about 52 C.

I balanced the rads as per faq, all now have a 12 deg C drop across all rads except a kick space heater which i didn't touch. (There are ball valves on its two supply flexible pipes so I could tweak that as well)

I haven't quite grasped the theory behind condensing boilers. Am I right in thinking that if the return is below 55 C then the boiler should be operating in condensing mode?

Thanks to all who replied to my original post: Fred, Ed and Dr D.

Francis Kirby

Reply to
a
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A temperature differential of 11 deg C is the ideal drop across a radiator the absolute maximum recommended is 16 deg C through really larger radiators. I am pretty sure if you read your boiler instruction manual you will find that a difference of 20 deg C is what you are looking for at your boiler. This can be achieved by altering pump speed or adjusting a bypass if one is fitted depending on your system layout. (I know your boiler does not require a bypass even if fitted to an S-plan as there is no pump overrun on it) Your boiler should be in condensing mode all the time if the temperature differential is correct.

Owl

Reply to
Awesometoday

Flow should be under 60c that is the highest temp for max efficency, go over and efficency drops, im sure its high efficency rating is at temps under 58- 60c. Eventualy you loose about 6% near 85c. Longer cycles are better also easier on equipment and longer run time at highest efficency level.

Reply to
ransley

Read here this will answer a few of your questions.

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Reply to
Awesometoday

Found a good graphic

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Reply to
a

thanks Owl and ransley

Have read some posts by Phil Addison and Andy Hall.

Downstairs rads are new and large and take nearly 20 c drop. Upstairs are old single panel, no fins and take a much smaller drop. We hope to replace these soon

trying for a 15/16 C drop, if my knees hold out :-)

Reply to
a

Maximum condensing efficiency is the "lowest" return temperature that can be obtained. Condensing "starts" at a notional 56C return water temperature.

This is where integral outside weather compensation promotes efficiency. With rads a typical flow temperature of 50C give given with an outside temperature of 10C. balance to give 20C across the rads and boiler that gives a return temperatures of 30C, which is very high efficiency. At 15C outside temperature the flow temperature will rise and even greater efficiency. It is done by modulating the burner. External stand-alone weather compensators can be fitted tending to switch the burner on and off to obtained the temperatures.

Only on start up from cold and outside temperatures near or are below freezing will the return temperatures rise above condensing dew-point - but very rare, and never with rads sized for 60-40C. Room temperature influence can be incorporated that lowers the boiler temperature even more when inside air room temperature nears, or is reached.

Unfortunately most boilers are selected and fitted by "plumbers" who know next to nothing about heating control or boiler operation. Plumbers should stick to drains. Get heating engineers.

Reply to
Doctor Drivel

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