{"id":57512,"date":"2026-09-29T16:07:43","date_gmt":"2026-09-29T15:07:43","guid":{"rendered":"https:\/\/ecoforest.com\/?p=57512"},"modified":"2026-09-29T16:07:43","modified_gmt":"2026-09-29T15:07:43","slug":"air-source-heat-pumps-with-aluminum-radiators-what-flow-temperature-do-you-need-to-stay-warm","status":"publish","type":"post","link":"https:\/\/ecoforest.com\/en\/news\/air-source-heat-pumps-with-aluminum-radiators-what-flow-temperature-do-you-need-to-stay-warm\/","title":{"rendered":"Air-source heat pumps with aluminum radiators: What flow temperature do you need to stay warm?"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">One of the most common concerns when considering an <a href=\"https:\/\/ecoforest.com\/en\/heat-pumps\/air-source-heat-pumps\/\" data-type=\"page\" data-id=\"1668\">air-source heat pump<\/a> is whether it can heat existing radiators. The short answer is yes, but there are technical considerations worth understanding before accepting a quote. In this article, we break down the physics of the problem, the flow temperature aluminum radiators require, and which models in Ecoforest\u2019s ecoAIR\u207a range are equipped for the job.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">The crux of the problem: flow temperature vs. the emitter\u2019s design temperature<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Every heating system is designed for a flow temperature (T<sub>imp<\/sub>) and a return temperature (T<sub>ret<\/sub>). Traditional gas boiler systems operate at T<sub>imp<\/sub> = 70\u201380 \u00b0C. <strong>Air-source heat pumps<\/strong> are more efficient at lower temperatures: their COP (Coefficient of Performance) ranges from 4\u20135 at a flow temperature of 35 \u00b0C and falls to around 2.5\u20133 when they are required to exceed 55 \u00b0C.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is where the type of heat emitter matters. A cast-iron radiator sized for 75\/65 \u00b0C cannot perform well at 45 \u00b0C: it simply does not emit enough heat. A <strong>low-profile aluminum radiator<\/strong>, however, can deliver the same heat output at flow temperatures between 45 \u00b0C and 55 \u00b0C thanks to its larger heat-exchange surface and better thermal conductivity \u2014 the optimal operating range for most modern heat pumps.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Why does aluminum change the equation?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Aluminum\u2019s thermal conductivity (~237 W\/m\u00b7K) is approximately ten times that of conventional steel and twenty times that of cast iron. This has two practical consequences:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Larger effective heat-emitting surface:<\/strong> heat is distributed more evenly across the radiator\u2019s entire fin.<\/li>\n\n\n\n<li><strong>Lower thermal inertia:<\/strong> the system responds more quickly to changes in demand, something the Inverter technology in ecoAIR\u207a heat pumps takes full advantage of.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The result is that a correctly sized aluminum radiator can achieve its rated design output with a T<sub>imp<\/sub> of <strong>45\u201355 \u00b0C<\/strong>, while a cast-iron equivalent would need 70\u201375 \u00b0C for the same room. That 20\u201325 \u00b0C difference in flow temperature translates directly into a <strong>COP up to 30\u201340% higher<\/strong> for the heat pump.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">The flow temperature you need: a guide<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Type of heat emitter<\/th><th>Required flow temperature<\/th><th>Compatible with standard air-source heat pumps<\/th><th>Estimated ecoAIR\u207a COP<\/th><\/tr><\/thead><tbody><tr><td>Underfloor heating<\/td><td>30\u201340 \u00b0C<\/td><td>\u2705 Optimal<\/td><td>4.5\u20135.0<\/td><\/tr><tr><td>Fan coil<\/td><td>40\u201345 \u00b0C<\/td><td>\u2705 Very good<\/td><td>4.0\u20134.5<\/td><\/tr><tr><td>Aluminum radiator (low-profile)<\/td><td>45\u201355 \u00b0C<\/td><td>\u2705 Good with EVI or HTR<\/td><td>3.0\u20133.5<\/td><\/tr><tr><td>Conventional steel\/cast-iron radiator<\/td><td>65\u201380 \u00b0C<\/td><td>\u26a0\ufe0f Only with HTR (higher consumption)<\/td><td>2.0\u20132.5<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Indicative values for outdoor conditions of 7 \u00b0C according to EN 14825. Actual COP depends on insulation, weather conditions, and system\nsizing.<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">EVI technology: the bridge between air-source heat pumps and radiators<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">For systems with aluminum radiators requiring flow temperatures of up to 55\u201360 \u00b0C, Ecoforest incorporates <strong>EVI (Enhanced Vapor Injection)<\/strong> technology into the <strong>ecoAIR\u207a EVI 4-20<\/strong> model. EVI injects medium-pressure refrigerant vapor directly into the SCROLL compressor, increasing heating capacity when the temperature difference is large and allowing the system to reach flow temperatures that a conventional refrigeration cycle could not maintain efficiently.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The ecoAIR\u207a EVI 4-20 uses natural R290 refrigerant (propane), positioning it to comply with <a href=\"https:\/\/ecoforest.com\/en\/news\/r290-in-air-source-heat-pumps-regulations-safety-and-efficiency-in-2025\/\">European F-Gas regulations<\/a> over the long term and reducing the system\u2019s environmental impact.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">HTR: High temperatures for the most demanding applications<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">When the radiators cannot be resized and the system requires flow temperatures above 60 \u00b0C (or direct domestic hot water up to 80 \u00b0C without an auxiliary electric heater), Ecoforest has developed <strong>HTR (High Temperature Range)<\/strong> technology. It is the <a href=\"https:\/\/ecoforest.com\/en\/news\/ecoforest-launches-the-first-air-source-heat-pump-with-superheater-dhw-up-to-80oc-at-no-additional-cost\/\">first air-source<br>heat pump to reach a flow temperature of 80 \u00b0C without additional energy consumption<\/a>, a milestone that makes energy retrofits possible without<br>having to replace existing radiators.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For systems with medium- to high-profile aluminum radiators and a T<sub>imp<\/sub> between 55 and 65 \u00b0C, this technology maintains a competitive COP\nwhere other products on the market already rely on electric resistance heating, driving up consumption.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Recommended Ecoforest models for systems with aluminum radiators<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The <a href=\"https:\/\/ecoforest.com\/en\/home-2\/attachment\/aerotermia-2\/\">Ecoforest ecoAIR\u207a range<\/a> covers 7 to 24 kW in a monobloc configuration,\nallowing the system to be sized correctly without oversizing it (a critical factor in keeping COP high):<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>ecoAIR\u207a 1-7 PRO<\/strong> \u2014 Monobloc, natural refrigerant, Inverter technology. For homes of up to ~100 m\u00b2 with correctly sized low-profile aluminum radiators.<\/li>\n\n\n\n<li><strong>ecoAIR\u207a 1-9 PRO<\/strong> \u2014 Inverter + SCROLL compressor. Ideal for 100\u2013130 m\u00b2 homes with aluminum heat emitters and moderate insulation.<\/li>\n\n\n\n<li><strong>ecoAIR\u207a 3-12 PRO \/ 3-18 PRO<\/strong> \u2014 For homes of 130\u2013200 m\u00b2 or those with higher demand due to poorer insulation. The 3-18 PRO is particularly suitable if a high T<sub>imp<\/sub> is expected.<\/li>\n\n\n\n<li><strong>ecoAIR\u207a EVI 4-20<\/strong> \u2014 The most technically robust option for systems with aluminum radiators requiring T<sub>imp<\/sub> \u2265 50 \u00b0C. EVI injection ensures stability and efficiency under these conditions.<\/li>\n\n\n\n<li><strong>ecoAIR\u207a 6-24 PRO<\/strong> \u2014 For large homes or small buildings. R290, Inverter, and SCROLL. Consult an authorized installer about compatibility with existing radiators.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">All ecoAIR\u207a models feature Copeland Inverter technology, with Ecoforest being the first manufacturer to introduce it across its range. This allows the compressor to continuously adjust its speed, matching output precisely to demand at any given moment \u2014 key to avoiding short cycling when aluminum radiators respond quickly to temperature changes.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Checks to make before installation<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Air-source heat pumps with aluminum radiators are technically viable, but the installer must first check:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Radiator sizing:<\/strong> if the original system was designed for 75\/65 \u00b0C, the heat-emitting surface will need to be increased (with more sections per radiator) to operate properly at 50\/40 \u00b0C. As a guide, reducing the flow temperature from 75 \u00b0C to 50 \u00b0C may require 1.5 to 2 times as much heat-emitting surface.<\/li>\n\n\n\n<li><strong>Home insulation:<\/strong> the lower the energy demand per m\u00b2, the lower the T<sub>imp<\/sub> required. A properly insulated home can operate perfectly well at 45 \u00b0C even when outdoor temperatures reach -5 \u00b0C.<\/li>\n\n\n\n<li><strong>Bleeding the circuit:<\/strong> mixed systems (combining aluminum and steel) are at risk of galvanic corrosion. Inhibitor additives and, where appropriate, hydraulic separators are essential.<\/li>\n\n\n\n<li><strong>Thermostatic valves:<\/strong> room-by-room control with thermostatic radiator valves improves overall COP by reducing the T<sub>imp<\/sub> required outside peak hours.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">For more details on installation in existing homes, see our article on <a href=\"https:\/\/ecoforest.com\/en\/news\/is-it-possible-to-install-aerothermal-energy-in-a-house-already-built\/\">how to install an air-source heat pump in an existing home<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How much can I save with an air-source heat pump compared with a gas boiler using the same radiators?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">With a T<sub>imp<\/sub> of 50 \u00b0C and a seasonal COP of 3.0 in Spain\u2019s average climate zone, an air-source heat pump consumes one-third of the final energy<br>that a gas boiler would consume (effective COP = 0.85\u20130.90). Even with the current electricity-to-gas price difference, bill savings can<br>exceed 40\u201350% in mild climates. <a href=\"https:\/\/ecoforest.com\/en\/news\/how-much-can-we-save-with-an-air-source-heat-pump\/\">Find out how much you can save with an air-source heat pump in your climate zone.<\/a><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Air-source heat pumps with aluminum radiators vs. underfloor heating: which is better?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Underfloor heating remains the optimal heat emitter for air-source heat pumps (T<sub>imp<\/sub> 30\u201340 \u00b0C = maximum COP), but it involves work on the floors, which is not\nalways feasible. Low-profile aluminum radiators are the second most efficient option and make it possible to <a href=\"https:\/\/ecoforest.com\/en\/news\/air-source-heat-pumps-in-older-flats-with-radiators-actual-flow-temperature-energy-consumption-and-solutions\/\">retrofit older systems at a much lower cost<\/a>.\nIf you are deciding between the two, read our comparison of <a href=\"https:\/\/ecoforest.com\/en\/news\/radiators-or-underfloor-heating-learn-the-differences\/\">radiators and underfloor heating<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Technical Specifications \u2014 ecoAIR\u207a Range<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th>Model<\/th><th>Heating capacity<\/th><th>Compressor technology<\/th><th>Refrigerant<\/th><th>Configuration<\/th><th>Distinguishing technology<\/th><\/tr><\/thead><tbody><tr><td>ecoAIR\u207a 1-7 PRO<\/td><td>7 kW<\/td><td>Copeland Inverter<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>\u2014<\/td><\/tr><tr><td>ecoAIR\u207a 1-9 PRO<\/td><td>9 kW<\/td><td>Inverter + SCROLL<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>\u2014<\/td><\/tr><tr><td>ecoAIR\u207a 3-12 PRO<\/td><td>12 kW<\/td><td>Inverter + SCROLL<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>\u2014<\/td><\/tr><tr><td>ecoAIR\u207a 3-18 PRO<\/td><td>18 kW<\/td><td>Inverter + SCROLL<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>\u2014<\/td><\/tr><tr><td>ecoAIR\u207a EVI 4-20<\/td><td>20 kW<\/td><td>Inverter + SCROLL<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>EVI (high flow temperature)<\/td><\/tr><tr><td>ecoAIR\u207a 6-24 PRO<\/td><td>24 kW<\/td><td>Inverter + SCROLL<\/td><td>R290 (natural)<\/td><td>Monobloc<\/td><td>\u2014<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Source: official Ecoforest technical documentation. COP according to EN 14825. All models provide cooling and heating simultaneously and can be integrated\nwith domestic hot water production.<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Using an air-source heat pump with aluminum radiators is not a technical compromise; it is a perfectly viable combination when the system is<br>correctly sized. The key is the flow temperature: <strong>45\u201355 \u00b0C is the operating range where low-profile aluminum radiators and the ecoAIR\u207a range meet<\/strong> to offer the best balance of comfort and energy efficiency. For systems with greater heating requirements, the EVI technology in the ecoAIR\u207a EVI 4-20 or HTR technology are Ecoforest\u2019s engineering solutions to the challenge of replacing gas boilers without changing the heat emitters.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If you want to learn more about how air-source heat pumps work with different heating systems, read our <a href=\"https:\/\/ecoforest.com\/en\/news\/complete-guide-to-heat-pumps\/\">complete guide to heat pumps<\/a> or discover the <a href=\"https:\/\/ecoforest.com\/en\/blog\/five-reasons-to-install-air-source-heat-pumps-in-your-home\/\">5 reasons to install an air-source heat pump in your home<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>One of the most common concerns when considering an air-source heat pump is whether it can heat existing radiators. The short answer is yes, but there are technical considerations worth understanding before accepting a quote. In this article, we break down the physics of the problem, the flow temperature aluminum radiators require, and which models [&hellip;]<\/p>\n","protected":false},"author":17,"featured_media":699,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"default","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center 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