{"id":56912,"date":"2015-12-01T14:47:42","date_gmt":"2015-12-01T12:47:42","guid":{"rendered":"http:\/\/wpcalc.com\/?p=56912"},"modified":"2025-05-09T09:42:10","modified_gmt":"2025-05-09T06:42:10","slug":"instantaneous-water-heater","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/engineering\/instantaneous-water-heater\/","title":{"rendered":"Instantaneous Water Heater Calculator"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 class=\"text-lg font-display font-bold\">Instantaneous Water Heating Performance Calculator<\/h2><\/div><div class=\"relative group inline-block\">\n  <button class=\"favorite\" id=\"favorite\" data-favorite-id=\"56912\" data-favorite-title=\"Instantaneous Water Heater\" data-favorite-url=\"https:\/\/wpcalc.com\/en\/engineering\/instantaneous-water-heater\/\" data-favorite-excerpt=\"This calculator helps you determine the required power of an instantaneous water heater or estimate the achievable water flow or temperature based on the heater\u2019s power. It\u2019s useful for engineers, plumbers, and homeowners planning water heating systems. Just input the desired temperature, cold water inlet temperature, and power or flow rate \u2014 and get instant results.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-pipeline\">\n    <span class=\"icon icon-shape-star-empty\"><\/span>\n  <\/button>\n  <div class=\"absolute right-full -translate-y-1\/2 top-1\/2 mr-2 w-max max-w-xs px-3 py-2 bg-gray-800 text-white text-xs rounded shadow-lg opacity-0 group-hover:opacity-100 transition-opacity duration-200 z-10 pointer-events-none\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/engineering\/instantaneous-water-heater\/\" method=\"POST\" class=\"calculator\" id=\"calculator-56912\" data-post=\"56912\"><fieldset class=\"fieldset-input is-1\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">Calculation mode<\/label><div class=\"grid grid-cols-1\"><select id=\"field-1\" name=\"calculation_mode\"><option value=\"performance\">Performance<\/option><option value=\"power\">Power heater (P)<\/option><option value=\"temperature\">Hot water temperature (Th)<\/option><\/select><svg class=\"pointer-events-none col-start-1 row-start-1 mr-2 size-5 self-center justify-self-end text-gray-500 sm:size-4\" viewBox=\"0 0 16 16\" fill=\"currentColor\" aria-hidden=\"true\" data-slot=\"icon\">\n              <path fill-rule=\"evenodd\" d=\"M4.22 6.22a.75.75 0 0 1 1.06 0L8 8.94l2.72-2.72a.75.75 0 1 1 1.06 1.06l-3.25 3.25a.75.75 0 0 1-1.06 0L4.22 7.28a.75.75 0 0 1 0-1.06Z\" clip-rule=\"evenodd\" \/>\n            <\/svg><\/div><\/div><div class=\"field has-term\" id=\"input-2\"><label for=\"field-2\">Power heater<\/label><div class=\"term\">P<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"power_heater\" id=\"field-2\" step=\"any\" value=\"3\"\/><div class=\"unit\">kW<\/div><\/div><div class=\"field has-term\" id=\"input-3\"><label for=\"field-3\">Cold water temperature<\/label><div class=\"term\">Tc<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"cold_water_temperature\" id=\"field-3\" step=\"any\" value=\"10\"\/><div class=\"unit\">\u00b0C<\/div><\/div><div class=\"field has-term\" id=\"input-4\"><label for=\"field-4\">Hot water temperature<\/label><div class=\"term\">Th<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"hot_water_temperature\" id=\"field-4\" step=\"any\" value=\"55\"\/><div class=\"unit\">\u00b0C<\/div><\/div><div class=\"field has-term\" id=\"input-5\" hidden><label for=\"field-5\">Water consumption<\/label><div class=\"term\">Q<\/div>  <div class=\"absolute bottom-0 left-16 top-8 w-2 h-0.5 bg-blue-500\"><\/div><input type=\"number\" name=\"water_consumption\" id=\"field-5\" step=\"any\" value=\"12\"\/><div class=\"unit\">L\/min<\/div><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"56912\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result is-column\" id=\"output-1\"><span class=\"field-value\" id=\"result-1\"><\/span><button class=\"copy-result\" data-tooltip=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\"><\/span><\/button><\/div><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"56912\" aria-live=\"polite\"><h2 class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/h2><div class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">0<\/span><span class=\"reaction text-3xl\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">0<\/span><span class=\"reaction text-3xl\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">0<\/span><span class=\"reaction text-3xl\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">0<\/span><span class=\"reaction text-3xl\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">0<\/span><span class=\"reaction text-3xl\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><ins class=\"adsbygoogle\"\n     style=\"display:block; text-align:center; margin: 32px 0;\"\n     data-ad-layout=\"in-article\"\n     data-ad-format=\"fluid\"\n     data-ad-client=\"ca-pub-1721569815777345\"\n     data-ad-slot=\"6317458308\"><\/ins>\n<script>\n     (adsbygoogle = window.adsbygoogle || []).push({});\n<\/script>\n<p><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Water Heater Power, Flow, and Temperature Formulas<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\\[\\text{Performance (L\/min)} = \\frac{P}{(T_h &#8211; T_c) \\times 0.073}\\]\\[P = Q \\times (T_h &#8211; T_c) \\times 0.073\\]\\[T_h = \\frac{P + Q \\times 0.073 \\times T_c}{Q \\times 0.073}\\]<\/div>\r\n\t<\/figure>\r\n\t<br \/>\n<strong>Where:<\/strong><\/p>\n<ul>\n<li>$$P$$ is the power of the heater in kilowatts (kW)<\/li>\n<li>$$T_h$$ is the target hot water temperature (\u00b0C)<\/li>\n<li>$$T_c$$ is the cold water inlet temperature (\u00b0C)<\/li>\n<li>$$Q$$ is the flow rate in liters per minute (L\/min)<\/li>\n<li>0.073 is a constant derived from water heat capacity and unit conversion<\/li>\n<\/ul>\n<p>\r\n<\/section><br \/>\nThese formulas are commonly used in the design and selection of electric tankless (instantaneous) water heaters. By rearranging the equations, you can calculate:<\/p>\n<ul>\n<li>the required power based on desired flow and temperature difference<\/li>\n<li>the achievable flow rate for a given power    <\/li>\n<li>the hot water temperature based on input conditions<\/li>\n<\/ul>\n<p>This calculator supports efficient planning for residential and industrial hot water supply, especially in energy-optimized systems.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This calculator helps you determine the required power of an instantaneous water heater or estimate the achievable water flow or temperature based on the heater\u2019s power. It\u2019s useful for engineers, plumbers, and homeowners planning water heating systems. Just input the desired temperature, cold water inlet temperature, and power or flow rate \u2014 and get instant results.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[4],"tags":[35],"class_list":["post-56912","post","type-post","status-publish","format-standard","hentry","category-engineering","tag-pipeline"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/56912","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=56912"}],"version-history":[{"count":1,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/56912\/revisions"}],"predecessor-version":[{"id":63936,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/56912\/revisions\/63936"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=56912"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=56912"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=56912"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}