A Conundrum - Gas boiler flow temperature versus Off Peak cylinder heating.

[Deleted User]

My 250L hot water cylinder has happily been re-heated over the past 8 months from PV solar. Now that my PV solar output is falling, I am trying to work out the best way forward.

I am on GoFaster at 8.5p/kWh and my gas Is on Tracker capped at 6p/kWh. My stats show that electric hot water re-heating uses 60% of what I would use with gas (boiler efficiency; pipe runs etc).  As I have a system boiler and unvented cylinder, I cannot just turn down the boiler flow temperature without thinking about the temperature of the water in the HW cylinder.  

That said, I am considering turning down my boiler flow temperature to 50C, and re-heating my cylinder overnight when required from GoFaster to see how it pans out. Sadly, I cannot find any definitive research on energy savings versus gas boiler flow return temperatures. 

Reed_Richards

Dolor said:

Sadly, I cannot find any definitive research on energy savings versus gas boiler flow return temperatures. 

Well the curve in figure 3.3 here https://www.purmo.com/au/clever/guide-the-increasing-use-of-low-temperature-water-systems.htm showing efficiency versus versus gas boiler flow return temperature appears quite frequently.  And this article cites the original source.