# Heat Demand vs Calculated **URL:** \ **Category:** Hardware\ **Tags:** vaillant\ **Created:** [20 October 2026 18:22 UTC](https://community.openenergymonitor.org/t/heat-demand-vs-calculated/30512 "2026-10-20T18:22:26Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![ispookie666](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/ispookie666/32/37885_2.png) [@ispookie666](https://community.openenergymonitor.org/u/ispookie666)\ **Post date:** [20 October 2026 18:22 UTC](https://community.openenergymonitor.org/t/heat-demand-vs-calculated/30512/1 "2026-10-20T18:22:26Z")
Our Vaillant Arotherm + 10Kw has been running for a good few months and coming up to first winter. ![image](https://community.openenergymonitor.org/uploads/default/original/3X/5/0/501e88073d79055fa70c4775901e42d5f25ee0a8.png) Everything is working good, the HP is cycling 60min and running for roughly 15 ish minutes(we have not had any seriously cold days). I’m fairly certain our heat loss is closer to what the calculated one is, as we have been using a 7.5Kw Mitsubishi Aircon for heating for the last few years, and it used to keep most of the downstairs warm except on the very cold days. Our hot water cylinder is in the Garage (not insulated or heated) Is it normal to see a big difference between the **Calculated Heat loss (8.07 Kw)** and **Heat Demand 2.53 Kw)**? Or is this just due to lack of data, I had a peruse around a few other systems and could not find any others with such a big difference. ---
**Author:** ![Galicia](https://community.openenergymonitor.org/user_avatar/community.openenergymonitor.org/galicia/32/37600_2.png) [@Galicia](https://community.openenergymonitor.org/u/Galicia)\ **Post date:** [20 October 2026 19:33 UTC](https://community.openenergymonitor.org/t/heat-demand-vs-calculated/30512/2 "2026-10-20T19:33:28Z")
Hi ispookie666, I think you do need more cold weather days in the data set. Keep gathering data over the next 4 months. Good luck, Frank