{"id":13083,"date":"2026-07-29T07:38:29","date_gmt":"2026-07-29T07:38:29","guid":{"rendered":"https:\/\/8ruiyan.com\/?p=13083"},"modified":"2026-07-29T07:38:49","modified_gmt":"2026-07-29T07:38:49","slug":"air-heaters-14","status":"publish","type":"post","link":"https:\/\/8ruiyan.com\/it\/air-heaters-14\/","title":{"rendered":"Duct Air Heater Air Resistance \u2013 How Big Is It, Really?"},"content":{"rendered":"<p class=\"wp-block-paragraph\">When specifying a duct air heater <a href=\"https:\/\/8ruiyan.com\/en\/all-air-heaters\/\">https:\/\/8ruiyan.com\/en\/all-air-heaters\/<\/a>, one of the first performance questions engineers ask is:\u00a0<em>How much air resistance will it add to the system?<\/em>\u00a0The answer is not a simple yes or no\u2014it depends on element geometry, fin density, and face velocity. However, the air resistance is always measurable and must be treated as a key system parameter, not an afterthought.<\/p>\n\n\n\n<div class=\"wp-block-uagb-image uagb-block-89d7344c wp-block-uagb-image--layout-default wp-block-uagb-image--effect-static wp-block-uagb-image--align-none\"><figure class=\"wp-block-uagb-image__figure\"><img loading=\"lazy\" decoding=\"async\" srcset=\"https:\/\/8ruiyan.com\/wp-content\/uploads\/2026\/07\/233cf76a01ef153e66251428f892d74f-1024x840.jpg ,https:\/\/8ruiyan.com\/wp-content\/uploads\/2026\/07\/233cf76a01ef153e66251428f892d74f.jpg 780w, https:\/\/8ruiyan.com\/wp-content\/uploads\/2026\/07\/233cf76a01ef153e66251428f892d74f.jpg 360w\" sizes=\"auto, (max-width: 480px) 150px\" src=\"https:\/\/8ruiyan.com\/wp-content\/uploads\/2026\/07\/233cf76a01ef153e66251428f892d74f-1024x840.jpg\" alt=\"Air Resistance\" class=\"uag-image-13075\" width=\"1024\" height=\"840\" title=\"Air Resistance\" role=\"img\"\/><\/figure><\/div>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>1. Where does the resistance come from?<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The pressure loss is not caused by &#8220;heating&#8221; itself\u2014it is purely aerodynamic. The main contributors are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Flow obstruction<\/strong>\u00a0by the heating elements (tubular, finned, or open-coil).<\/li>\n\n\n\n<li><strong>Turbulence generation<\/strong>\u00a0around supports, terminal blocks, and mounting flanges.<\/li>\n\n\n\n<li><strong>Velocity redistribution<\/strong>\u00a0\u2013 the heater forces the air to accelerate through narrow gaps between elements, then decelerate, creating permanent pressure losses.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">In short, the heater acts like a compact heat exchanger with a built-in flow restriction.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>2. Typical magnitude \u2013 a realistic range<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">For most forced-air applications (velocity 2.5 to 5 m\/s, finned tubular elements):<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th class=\"has-text-align-left\" data-align=\"left\">Configuration<\/th><th class=\"has-text-align-left\" data-align=\"left\">Pressure Drop (Pa)<\/th><th class=\"has-text-align-left\" data-align=\"left\">Pressure Drop (inH\u2082O)<\/th><\/tr><\/thead><tbody><tr><td>Sparse, bare-tube elements<\/td><td>40 \u2013 100<\/td><td>0.16 \u2013 0.40<\/td><\/tr><tr><td>Standard finned elements<\/td><td>150 \u2013 350<\/td><td>0.60 \u2013 1.40<\/td><\/tr><tr><td>High-density fins or compact pitch<\/td><td>400 \u2013 800+<\/td><td>1.60 \u2013 3.20+<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">These values are&nbsp;<strong>moderate<\/strong>&nbsp;compared to a wet cooling coil (which often exceeds 500 Pa) but&nbsp;<strong>significant<\/strong>&nbsp;compared to an empty duct section (near zero).<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>3. The square-law effect \u2013 velocity matters most<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The pressure drop scales approximately with the&nbsp;<strong>square of air velocity<\/strong>:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">\u0394P \u221d V\u00b2<\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">This means:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Increasing airflow by 20% raises resistance by ~44%.<\/li>\n\n\n\n<li>Reducing face velocity from 5 m\/s to 3.5 m\/s can cut the pressure drop by nearly half.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, if your fan is already tight on static pressure, reducing velocity (by enlarging the heater cross-section) is the most effective remedy.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>4. Operating temperature also plays a role<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Hot air is less dense than cold air. At 200\u00b0C, air density drops to about 75% of its value at 20\u00b0C. Since dynamic pressure is proportional to density, the actual pressure drop at high temperatures is&nbsp;<strong>lower<\/strong>&nbsp;than at cold start-up.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Always size the fan for the&nbsp;<strong>cold start condition<\/strong>&nbsp;\u2013 that is when the resistance peaks.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>5. Why this matters for system design<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Ignoring heater pressure drop leads to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Under-sized fans, resulting in insufficient airflow.<\/li>\n\n\n\n<li>Overheated elements due to low mass flow (trip on high-limit thermostats).<\/li>\n\n\n\n<li>Poor temperature uniformity across the duct.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">On the other hand, over-estimating it leads to over-sized fans, higher capital cost, and unnecessary energy consumption.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>6. Practical recommendations<\/strong><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Ask for the \u0394P curve<\/strong>\u00a0from the manufacturer \u2013 not just a single point.<\/li>\n\n\n\n<li><strong>Match the heater face area<\/strong>\u00a0to your duct size. A common rule: keep face velocity \u2264 4 m\/s for finned heaters if pressure drop is a concern.<\/li>\n\n\n\n<li><strong>Consider element orientation<\/strong>\u00a0\u2013 horizontal vs. vertical mounting can affect flow distribution and localized losses.<\/li>\n\n\n\n<li><strong>Use CFD or manufacturer software<\/strong>\u00a0for critical applications \u2013 empirical hand-calculations often miss entry\/exit losses.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Final takeaway<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">In short, the air resistance of a duct air heater is neither trivial nor unmanageable. It is a predictable consequence of compact heat transfer. With proper velocity selection, accurate fan sizing, and reliable performance data from the manufacturer, this air resistance becomes a routine design input\u2014not a source of uncertainty. Think of it as the cost of doing business in thermal engineering: pay it with good design, and the system will perform as expected.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For further problems about electric air heater, please contact our technical team for expert advice.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Whatsapp:86-19106101570<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">wechat:86-19106101570<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">email:fob@jsryan.com<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"http:\/\/www.8ruiyan.com\/\">http:\/\/www.8ruiyan.com<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>","protected":false},"excerpt":{"rendered":"<p>When specifying a duct air heater https:\/\/8ruiyan.com\/e [&hellip;]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","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":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[1],"tags":[],"class_list":["post-13083","post","type-post","status-publish","format-standard","hentry","category-blog"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v25.1 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Air Resistance in Duct Heaters \u2013 How High Is It?<\/title>\n<meta name=\"description\" content=\"Air resistance in duct heaters is predictable. 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