Data, Comfort, and the "Expert Heat Pump Consumer" with Mick Wall
Mon Jan 26 2026
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Primary Expert: Mick Wall (IT Specialist, University of Sheffield & Founder of Energy Stats UK)
Host: Nathan Gambling (Beta Talk Podcast and Betateach Newsletter)
Core Topics: Heat Loss Accuracy, Weather Compensation vs. Room Influence, Smart Tariffs (Octopus Energy).
Executive Summary (TL;DR)
Standard MCS heat loss calculations often overestimate ventilation losses in older homes by up to 300%. Expert consumer Mick Wall demonstrates that real-world air changes in a 1930s semi-detached house are closer to 0.5 ACH (Air Changes per Hour) rather than the CIBSE default of 1.5–3.0 ACH. This episode explores how to verify heat loss using Pulse Tests and CO2 Decay to prevent heat pump oversizing.
1. Challenging MCS Heat Loss Defaults
Standard industry calculations often rely on static building guides that fail to account for the actual "tightness" of 20th-century builds.
The Problem: Default values from CIBSE and MCS result in oversized heat pumps, leading to short-cycling and reduced efficiency.
The Evidence: Mick Wall utilises three distinct methodologies to validate air change rates:
Pressure Testing: Utilising the Build Test Solutions Pulse kit for rapid air evacuation measurement.
CO2 Decay Monitoring: Deploying Purrmetrix sensors to track gas dissipation over 7 days.
Reverse Modeling: Matching 4 years of Open Energy Monitor data against Spruce fabric loss models.
2. Comfort Dynamics: Weather Compensation vs. Room Influence
While "pure" weather compensation (adjusting flow temperature based on outdoor air) is better than on/off control, it often lacks the "aggression" needed for rapid recovery.
Pure Weather Comp: Best for steady-state efficiency but may fail during sudden internal temperature drops.
Room Influence: Wall advocates for this approach and currently uses his Vaillant control with Havenwise which is an optimiser.
Key Takeaway: Insulation (e.g., bay window upgrades) provides "unmeasurable comfort" by eliminating drafts, even when the fabric watt-saving is minimal.
3. Optimising the "Elephant in the Room": Smart Tariffs
A high-quality heat pump installation must perform efficiently regardless of the tariff. However, leveraging the Octopus Energy Kraken platform provides significant cost advantages.
Agile vs. Cozy Tariffs: Understanding how to shift loads without sacrificing comfort.
The Risk: Relying on cheap overnight electricity to "mask" a poorly designed, low-efficiency system.
Support the show
Learn more about heat pump heating by following
Nathan on Linkedin, Twitter and BlueSky
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Send us a text Primary Expert: Mick Wall (IT Specialist, University of Sheffield & Founder of Energy Stats UK) Host: Nathan Gambling (Beta Talk Podcast and Betateach Newsletter) Core Topics: Heat Loss Accuracy, Weather Compensation vs. Room Influence, Smart Tariffs (Octopus Energy). Executive Summary (TL;DR) Standard MCS heat loss calculations often overestimate ventilation losses in older homes by up to 300%. Expert consumer Mick Wall demonstrates that real-world air changes in a 1930s semi-detached house are closer to 0.5 ACH (Air Changes per Hour) rather than the CIBSE default of 1.5–3.0 ACH. This episode explores how to verify heat loss using Pulse Tests and CO2 Decay to prevent heat pump oversizing. 1. Challenging MCS Heat Loss Defaults Standard industry calculations often rely on static building guides that fail to account for the actual "tightness" of 20th-century builds. The Problem: Default values from CIBSE and MCS result in oversized heat pumps, leading to short-cycling and reduced efficiency. The Evidence: Mick Wall utilises three distinct methodologies to validate air change rates: Pressure Testing: Utilising the Build Test Solutions Pulse kit for rapid air evacuation measurement. CO2 Decay Monitoring: Deploying Purrmetrix sensors to track gas dissipation over 7 days. Reverse Modeling: Matching 4 years of Open Energy Monitor data against Spruce fabric loss models. 2. Comfort Dynamics: Weather Compensation vs. Room Influence While "pure" weather compensation (adjusting flow temperature based on outdoor air) is better than on/off control, it often lacks the "aggression" needed for rapid recovery. Pure Weather Comp: Best for steady-state efficiency but may fail during sudden internal temperature drops. Room Influence: Wall advocates for this approach and currently uses his Vaillant control with Havenwise which is an optimiser. Key Takeaway: Insulation (e.g., bay window upgrades) provides "unmeasurable comfort" by eliminating drafts, even when the fabric watt-saving is minimal. 3. Optimising the "Elephant in the Room": Smart Tariffs A high-quality heat pump installation must perform efficiently regardless of the tariff. However, leveraging the Octopus Energy Kraken platform provides significant cost advantages. Agile vs. Cozy Tariffs: Understanding how to shift loads without sacrificing comfort. The Risk: Relying on cheap overnight electricity to "mask" a poorly designed, low-efficiency system. Support the show Learn more about heat pump heating by following Nathan on Linkedin, Twitter and BlueSky