@derek-m my heat loss is very linear. So linear in fact the trendline is 93% accurate

tbh if you guys are into this this much you should contact homely, they will sell you a device which hacks into the midea unit and tweaks the output as it learns the heat loss of your house giving the optimum curve. try it here, ive seen it work on the midea, it is very impressive, me i have a RED, it just gets on with it on its own. https://www.homelyenergy.com/

tell them i sent you 

@grahamh I'll take a look - as a side note, what a terrible website. It doesn't say anywhere what they actually do, or how it works.

thats techys for you 

I will be on a heating measurement adventure in the loft in the next day or two. My aim? To discover what my low loss header is actually doing. Specifically I want to know which of the below scenarios represents my current system.

Potentially I might just buy one of these - LINK - as its basically disposable (£20) and will give me 4 temperature sensors I can just install and use the app to monitor, rather than camp in the loft.

@batalto 

I like the thermometer in the link and think I'll get one.  

@kev-m its £16 after discount. As long as its mostly accurate its fine for my needs.

@kev-m its arrived and I have to say I am impressed by the little device. I can do it all over the app and it provides me some graphs which I can use to track the readings from the monitor. It came with 4 probes, but can handle 6 - for my imprecise needs its ideal.

Now I just need to install the little guy in the loft

RESULTS - both my heating circuits are running (upstairs and down) and it would appear my low loss header is just that... low loss. In fact it seems to be operating almost perfectly. The numbers basically match at top and bottom. I cant see any evidence of mixing of water. One slight concern is that HP shows 41 degrees on its own curve, yet the temperature prior to the LLH is 37. There could be some losses on the way, but I doubt 4 degrees. However my measurements are just meat thermometers shoved inside the pipe lagging next to the pipe. Still the main concern was LLH losses causing in efficiency and this seems to be dispelled for me.

I am just going to leave it logging until the battery dies (apparently 200hrs, we shall see) and then I can review what might happen.

Good result.  I've ordered one of the thermometers.  It will be good for checking and collecting evidence that my ASHP's sensors aren't recording properly.

Current total power purchased this month is at 532kW so far - from the heat pump hard monitor, its used 426kW, which is less than the internal app says its used. So far, given the cold, I am pretty happy. On track to use around 1.5MW in December @ a nominal 15p/kw (ignoring GO tariff) that would be approx £225.

My usual DD is £134 a month and December is supposed to be around 15% of your total heating bill (or two months worth of DD). I would say I am on track and so far pleased with my results. The house is a toasty 21 degrees all day and night.

For context last December I used 5,765kW of gas for heating and hot water.

Posted by: @batalto

Current total power purchased this month is at 532kW so far - from the heat pump hard monitor, its used 426kW, which is less than the internal app says its used. So far, given the cold, I am pretty happy. On track to use around 1.5MW in December @ a nominal 15p/kw (ignoring GO tariff) that would be approx £225.

My usual DD is £134 a month and December is supposed to be around 15% of your total heating bill (or two months worth of DD). I would say I am on track and so far pleased with my results. The house is a toasty 21 degrees all day and night.

For context last December I used 5,765kW of gas for heating and hot water.

Sounding good. 

As a comparison were you getting a toasty 21 degrees day and night when you were using 5765kw of gas?