Flow and return temperature.

[Joe82]

Morning,
Quick question just because I like to know how things work.
Am I right in thinking that the boiler thermostat controls the flow temperature?
And in order to get the correct return temperature you have to have a correctly balanced system.
Thanks in advance

 

[Dan Robinson]

More or less.

 

[AngelesPlumbing]

Youre nearly right but boiler thermostat is the temperature water inside the boiler, heating flow is heated from boiler coming out to distribute to radiators,cylinder & etc. and heating return is coming back from heating system to return to the boiler to be re-heated then goes to flow again. So its normal the heating return is colder than the heating flow.

 

[Joe82]

Thanks for the replies.
How important is it to get these temperatures right?
What effect does it have on the system/boiler performance?

 

[Dan Robinson]

Don't overwhelm us with information please.

 

[AngelesPlumbing]

Thanks for the replies.
How important is it to get these temperatures right?
What effect does it have on the system/boiler performance?

Just look on manufactures instruction

 

[Jackrae]

Return temperature must be less than about 55 degrees centigrade for the boiler to provide condensate heat recovery. Above this return temperature condensing boilers do not condense - irrespective of what the manufacturer might claim. So running a boiler at 80 outlet and 60 return is less efficient than running one at 70 outlet and 50 return. Therefore radiators should be sized for inflow temperatures no higher than 70 degrees. Radiators are generally sized for a 20 centigrade degrees differential between inflow and outflow under "worst case" conditions. However this figure, at best, can only be a theoretical one as radiator differential depends on control valve position/setting, and room temperature. This is made even less predictive if you use thermostatic radiator valves.
Unless your boiler is fitted with a modulating burner control that sets the firing rate to maintain a fixed differential, the boiler thermostat simply acts as an ON-OFF device that fires up the boiler when it's outflow temperature is below the set temperature and then shuts the burner down when it reaches this temperature (plus/minus whatever the hysteresis of the thermostat is).

I stand to be corrected on all of the above

 

[Steelmasons]

Return temperature must be less than about 55 degrees centigrade for the boiler to provide condensate heat recovery. Above this return temperature condensing boilers do not condense

That will depend upon CO2% in flue gas.

I stand to be corrected on all of the above

See above.

 

[Joe82]

Thanks again for the replies.

 

[WabbitPoo]

Good luck with your assignment.