# Heat meter
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> Source: https://en.wikipedia.org/wiki/Heat_meter
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{{Short description|Measuring device for thermal energy}}
[[image:Wärmeübergabestation 300 kW.jpg|thumb|right|A heat meter attached to a [heat exchanger](/source/heat_exchanger) in a [district heating substation](/source/district_heating_substation) in a residential neighborhood in [Austria](/source/Austria). Right in white-blue: the calculator; in the center in bronze: the ultrasonic flow meter. ]]
A '''heat meter''', '''thermal energy meter''', or '''[BTU](/source/British_thermal_unit) meter''' is a device that measures [thermal energy](/source/thermal_energy) provided by a source, such as a [central heating](/source/central_heating) system, by measuring the flow rate of the [heat transfer fluid](/source/Heat-transfer_fluid) and the change in its temperature ([ΔT](/source/Temperature_gradient)) between the outflow and return legs of the system. Heat meters are used in [district heating](/source/district_heating) systems and other shared heating systems to measure heat delivered to residential and commercial tenants, which enables consumption-based billing ([submetering](/source/Utility_submeter)). Heat meters are also used in industrial plants for measuring [boiler](/source/boiler) output and heat taken by [process](/source/Process_manufacturing).
== Elements ==
thumb|Heat meter with ultrasonic flow meter
A heat meter consists of:[{{Cite web |date=January 2019 |title=Fundamentals of Heat Metering in Hydronic Systems - Idronics 24 |url=https://www.caleffi.com/sites/default/files/media/external-file/Idronics_24_NA_Fundamentals%20of%20heat%20metering%20in%20hydronic%20systems.pdf |access-date=2025-11-19 |website=Caleffi |page=5-6 |language=en-us}}]
# A fluid [flow meter](/source/Flow_measurement), typically a [turbine flow meter](/source/turbine_flow_meter) or [ultrasonic flow meter](/source/ultrasonic_flow_meter).
# A means of measuring the temperature between the outflow and the inflow, usually a pair of [thermocouples](/source/Thermocouple).
# A means of integrating the two measurements over a period of time and accumulating the total [heat transfer](/source/heat_transfer) in a given period.
== Applications ==
thumb|Early mechanical heat meter
Heat meters are commonly used in buildings served by [district heating](/source/district_heating). Operators of [multifamily residential](/source/multifamily_residential) buildings and multi-tenant commercial buildings with [hydronic systems](/source/Hydronics) can also use heat meters to [submeter](/source/Utility_submeter) tenant use of the system.[{{Cite web |last=Harris |first=Angela D. |date=2019-07-15 |title=Heat Metering Makes Centralized Hydronic Heat a Viable Option |url=https://www.achrnews.com/articles/141568-heat-metering-makes-centralized-hydronic-heat-a-viable-option |access-date=2025-11-19 |website=ACHR News |language=en}}]
In industrial plants, a thermal energy meter can be used to measure the cooling output from a [chiller](/source/chiller) unit,[{{Cite web |last=Rimler |first=Barry |date=February 20, 2013 |title=Sensors for Measuring Chilled Water Production and it's Uses |url=https://blog.se.com/datacenter/architecture/2013/02/20/sensors-measuring-chilled-water-production/ |access-date=19 November 2025 |website=Schneider Electric}}] for example to monitor functionality and energy efficiency.[{{Cite web |date=May 28, 2020 |title=Flow Monitoring in Process Cooling Applications |url=https://www.veris.com/blog/flow-monitoring-in-process-cooling-applications |access-date=19 November 2025 |website=Veris}}]
Heat metering can be used in [solar thermal collector](/source/solar_thermal_collector) systems to verify that the system is working correctly and quantify how much solar heat is collected.[{{Cite web |last=Stickney |first=Bristol |date=October 25, 2017 |title=Heat Energy Measurement Around a Primary Loop |url=https://www.phcppros.com/articles/6257-heat-energy-measurement-around-a-primary-loop |access-date=2025-11-19 |website=PHCP Pros |language=en}}] For example, an experimental solar water heating project in 1976 in [Ocala, Florida](/source/Ocala%2C_Florida), involved using heat meters to measure energy produced by the solar heaters.[{{Cite news |date=1976-10-07 |title=Solar Energy To Be Used As Water Heater |url=https://www.newspapers.com/article/the-daytona-beach-news-journal-solar-ene/185299218/ |access-date=2025-11-20 |work=The Daytona Beach News-Journal |pages=17}}]
== Regional practices and regulations ==
thumb|Example of heat meter installation
=== European Union ===
The [European Union](/source/European_Union) has encouraged per-tenant heat metering as an energy efficiency strategy since 2002, and it made heat metering mandatory in 2012 with the [Energy Efficiency Directive 2012/27/EU](/source/EU_Energy_Efficiency_Directive_2012).[{{Cite journal |last1=Canale |first1=L. |last2=Dell'Isola |first2=M. |last3=Ficco |first3=G. |last4=Cholewa |first4=T. |last5=Siggelsten |first5=S. |last6=Balen |first6=I. |date=2019-11-01 |title=A comprehensive review on heat accounting and cost allocation in residential buildings in EU |url=https://www.sciencedirect.com/science/article/pii/S0378778819316883 |journal=Energy and Buildings |volume=202 |article-number=109398 |doi=10.1016/j.enbuild.2019.109398 |bibcode=2019EneBu.20209398C |issn=0378-7788}}] This directive requires heat metering in multifamily residential buildings that use district heating or have a central heating system.[{{Citation |last1=Fabrizio |first1=E. |last2=Ferrara |first2=M. |last3=Monetti |first3=V. |title=Smart Heating Systems for Cost-Effective Retrofitting |date=2017-01-01 |work=Cost-Effective Energy Efficient Building Retrofitting |pages=279–304 |url=https://www.sciencedirect.com/science/chapter/edited-volume/abs/pii/B9780081011287000101 |access-date=2025-11-19 |publisher=Woodhead Publishing |language=en-US |doi=10.1016/b978-0-08-101128-7.00010-1 |isbn=978-0-08-101128-7 |url-access=subscription }}] For example, the [United Kingdom](/source/United_Kingdom) requires operators of communal heating systems to submeter tenant heat use.[{{Cite web |date=2023-12-18 |title=Heat meters |url=https://www.islington.gov.uk/housing/heat-meters |access-date=2024-02-22 |website=Islington Council |language=en}}][{{Cite web |date=2024-11-13 |title=Regulations: heat networks (metering and billing) |url=https://www.gov.uk/guidance/heat-networks |access-date=2025-11-19 |website=GOV.UK |language=en}}] The goal is to reduce energy consumption by providing tenants a financial incentive to reduce heat consumption.[{{Cite journal |last1=Morgenstern |first1=Paula |last2=Lowe |first2=Robert |last3=Chiu |first3=Lai Fong |date=2015-03-04 |title=Heat metering: socio-technical challenges in district-heated social housing |url=https://doi.org/10.1080/09613218.2014.932639 |journal=Building Research & Information |volume=43 |issue=2 |pages=197–209 |doi=10.1080/09613218.2014.932639 |bibcode=2015BuRI...43..197M |issn=0961-3218}}]
In the European Union, heat meters need to comply with the [Measuring Instruments Directive](/source/Measuring_Instruments_Directive) (MID) Annex VI MI-004 if the meters are used for [custody transfer](/source/custody_transfer). For [automatic meter reading](/source/automatic_meter_reading), they use the [Meter-Bus](/source/Meter-Bus) standard.
=== United States and Canada ===
Heat meters are typically called [BTU](/source/British_thermal_unit) meters in the United States and Canada. They were commercially available in the United States as early as 1958, under the brand name Pollux BTU Meter.[{{Cite news |date=1958-09-09 |title=New Device Tells Heat Absorption; Instrument Also Measures Amount of Cooling -- Use in Shopping Mart Cited |url=https://www.nytimes.com/1958/09/09/archives/new-device-tells-heat-absorption-instrument-also-measures-amount-of.html |access-date=2025-11-20 |work=The New York Times |language=en}}] As of the late 2010s and early 2020s, they are uncommon in the United States and Canada, but there is growing interest due to increasing energy costs and requirements to reduce [carbon emissions](/source/Greenhouse_gas_emissions).[{{Cite web |last=Siegenthaler |first=John |date=March 7, 2019 |title="Pay for what you use" heat metering technology gains traction |url=https://www.hpacmag.com/features/heat-meter-technology-gains-traction/ |access-date=2025-11-19 |website=HPAC Magazine |language=en-US}}][{{Cite web |last=Caswell |first=Logan |date=June 25, 2021 |title=Benefits of Energy Metering |url=https://www.hpacmag.com/features/benefits-of-energy-metering/ |access-date=2025-11-19 |website=HPAC Magazine |language=en-US}}]
The relevant standard is [ASTM](/source/ASTM_International) E3137/E3137M-18, "Standard Specification for Heat Meter Instrumentation", released in 2018.[{{Cite web |date=August 8, 2018 |title=Standard Specification for Heat Meter Instrumentation |url=https://store.astm.org/e3137_e3137m-18.html |access-date=2025-11-19 |website=ASTM |language=en}}]
=== China ===
[Northern China](/source/Northern_China) has a significant number of large residential buildings with district heating.[{{Cite journal |last1=Luo |first1=Ao |last2=Li |first2=Chunyang |last3=Xia |first3=Jianjun |last4=Cheng |first4=Pengyue |date=2024-01-25 |title=Thermal Characteristics and User Regulation of Household Heat Metering for Residential District Heating Systems in Northern China |journal=Energies |language=en |volume=17 |issue=3 |pages=579 |doi=10.3390/en17030579 |doi-access=free |issn=1996-1073 }}] As early as 2003, policymakers recommended meter-based heat pricing to improve the efficiency and sustainability of district heating, as part of larger heat reform initiatives.[{{Cite journal |last1=Wang |first1=Manyu |last2=Huang |first2=Ying |last3=An |first3=Zidong |last4=Wei |first4=Chu |date=2023-01-01 |title=Reforming the world's largest heating system: Quasi-experimental evidence from China |url=https://www.sciencedirect.com/science/article/pii/S0140988322005461 |journal=Energy Economics |volume=117 |article-number=106417 |doi=10.1016/j.eneco.2022.106417 |bibcode=2023EneEc.11706417W |issn=0140-9883|url-access=subscription }}] By 2015, 32 million heat meters were installed in buildings in urban areas of northern China.[{{Cite web |date=2017 |title=District Energy Systems in China: Options for optimisation and diversification |url=https://iea.blob.core.windows.net/assets/590cc681-349a-4a55-9d3f-609eff6cde0b/DistrictEnergySystemsinChina.pdf |access-date=2025-11-20 |website=International Energy Agency (IEA) |page=16, 20 |language=en-GB}}] As of 2024, relatively few buildings charged for per-household heat usage based on heat meters, but there was interest in improving the quality and distribution of heat metering.[{{Cite journal |last=Korppoo |first=Anna |last2=Korobova |first2=Nina |date=2012-03-01 |title=Modernizing residential heating in Russia: End-use practices, legal developments, and future prospects |url=https://www.sciencedirect.com/science/article/pii/S0301421511009761 |journal=Energy Policy |volume=42 |pages=213–220 |doi=10.1016/j.enpol.2011.11.078 |issn=0301-4215|url-access=subscription }}] At that time, between 10-25% of private houses and apartments with district heating had heat meters, along with 40% of public buildings.