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Posted

 

19/10/2025 8.30 am test: House temperature when heating hot water:

 

During this test no major actions in the home were happening that would effect the results. 

 

Outside Temperature 11°C   Weather no sun/raining/25mph wind - gusts to 30mph.

Home temp 22.7.

Hot water tank 205 litres

Buffer tank 36°C

Hot water starts calling

The difference between hot water demand turn on and turn off is a rise of 5.5°C

Hot water reaches temperature in 35 mins

Home temp after hot water demand is 22.7°C

Buffer tank 35.3°C

Home temperature during 30 minutes after hot water heating finished stayed at 22.7°C

 

In my opinion the time taken to bring the hot water tank up to temperature is suitable in duration (we are using low fan speed) and does not materially effect the home temperature when the outside temperature is 11°C. 

 

Posted
1 hour ago, Marvin said:

The difference between hot water demand turn on and turn off is a rise of 5.5°C

Measured after how long after turn off?

 

1 hour ago, Marvin said:

Outside Temperature 11°C 

At that temperature, I still don't need to heat the house. Usually start heating when the daily means is 9°C or less.

23°C IAT is a bit higher than my mean temperature, but not by much.

 

Are you going to try DWH at different times if the day to see if there is any difference?

Posted

Hi @SteamyTea

 

Hope your well...

 

This is the start of a test I am trying to do during the winter as this is the high use period.

The heating is programmed to be on permanently and will be on until the spring (a few degrees lower in the night but still on)

 

14 minutes ago, SteamyTea said:

Are you going to try DWH at different times of the day to see if there is any difference?

The hot water is programmed to come on when the tank temperature is below the 'on' until above the 'off' levels. the spread being 5.5°C, However I will stop that happening on occasions (when the outside temperature is lower than today, with no sunlight) to see what happens. You have made me think about it and I will record where the hot water temperature starts from in case it is below the level of 'demand' when it starts.

 

Other poster had been discussing what happened to the house temperature when the heat is diverted to heating up the hot tank. I realised this would be affected by the outside and inside environment and decided to record the result when possible. 

 

 

Posted

@Marvin

 

While I can see people's concerns about lack of space heating when the DHW is heating, I can't recall a time that people have actually had a problem.

There is no reason that DHW cannot be heated in smaller time steps i.e. half hour here and there, this is what PV to DHW diverters do.

 

One if the things I have tried to do at home is limit the maximum current that my house draws. So when the DHW is heating, I don't have the storage heaters recharging.

This is purely a game I play as my supply, at 100A is not at risk. 

The other game is increasing the length of time that my house draws zero power (well less that 1 Wh). I think 3 hours is my record. Must have had something defrosting in the fridge.

Putting those two games together means I can get a picture of how much energy needs to be stored, and how little needs to be delivered to keep the same living standards.

 

Do you have monitoring equipment that logs at the Wh level, or are you using the smart meters half hour averages?

 

  • Like 1
Posted

Hi @SteamyTea

 

No smart meter.

Energy used by ASHP goes through a separate meter first which only logs amount used.

PV is already monitored to turn things on and off with CT clamps measuring the power to the grid. Extremely rare to supply power to the grid in winter even if PV working at full capacity.

The Watt/hour level only peaks when doing serious cooking. Home background level is about 600w 

ASHP is in weather compensated mode and I wanted to see if the hot water is still adequate in lower temperatures. 

 

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