{"id":46,"date":"2021-02-11T18:18:58","date_gmt":"2021-02-11T23:18:58","guid":{"rendered":"https:\/\/opentextbc.ca\/basichvac\/chapter\/low-voltage-thermostats\/"},"modified":"2023-03-02T11:33:06","modified_gmt":"2023-03-02T16:33:06","slug":"low-voltage-thermostats","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/basichvac\/chapter\/low-voltage-thermostats\/","title":{"raw":"Low-Voltage Thermostats","rendered":"Low-Voltage Thermostats"},"content":{"raw":"Click play on the following audio player to listen along as you read this section.\r\n\r\nhttps:\/\/media.bccampus.ca\/id\/0_lqw37bvr?width=608&amp;height=80&amp;playerId=23449753\r\n\r\n<strong>[pb_glossary id=\"230\"]Low-voltage thermostats[\/pb_glossary]<\/strong> are smaller and cheaper to install and maintain, and the wiring does not need to have as high a voltage and power rating as their line-voltage counterparts. This is why <strong>[pb_glossary id=\"229\"]low-voltage control circuits[\/pb_glossary]<\/strong> are favoured for central heating units. Low voltage thermostats are also more sensitive to changes in heat than line-voltage thermostats, and so can provide more precise control.\r\n\r\nWhen controlling a single large heating unit, such as a <strong>[pb_glossary id=\"136\"]central gas furnace[\/pb_glossary]<\/strong> or <strong>[pb_glossary id=\"137\"]electric furnace[\/pb_glossary]<\/strong>, there is no zone control as with baseboard heaters; either the whole house is getting heated, or none of it is. A low-voltage thermostat installed in a central location, and powered by a <strong>[pb_glossary id=\"138\"]120 - 24V transformer[\/pb_glossary]<\/strong>, can senses the ambient temperature and be used to control a [pb_glossary id=\"139\"]<strong>relay<\/strong>[\/pb_glossary] to deliver power to the heating load.\r\n\r\nBy using an <strong>[pb_glossary id=\"204\"]extra-low-voltage[\/pb_glossary]<\/strong> source for the control circuit we get the benefit of lower cost and easier installation along with increased safety, allowing a simple two-wire low-voltage cable to be installed in an ideal location in the house. Because it is only meant to handle the control current and not the load current, low-voltage thermostats are highly responsive and can provide more accurate control than line-line voltage thermostats.\r\n\r\nSome models of low-voltage thermostats used to control central gas furnace or electric furnace loads incorporating heat exchanges and blowers, will have a small, series connected, resistive device called an <strong>[pb_glossary id=\"206\"]anticipator resistor[\/pb_glossary]<\/strong>. The purpose of this device is to fine tune the sensitivity of the thermostat and prevent overshoot of the desired room temperature.\r\n\r\nLow-voltage thermostats, fall into two general categories, some are simple temperature activated switches while others are more modern [pb_glossary id=\"225\"]<strong>electronic thermostats<\/strong>[\/pb_glossary] incorporating solid-state circuitry and allowing for programmable behaviours such as 24-hour cycles, and weekday vs weekend scheduling.\r\n\r\nElectronic thermostats use semiconductor components for both temperature sensing and control-circuit switching. If installed to replace an existing analogue thermostat, the electronic thermostat must have a separate power source, which is usually a battery.\r\n\r\n[caption id=\"attachment_312\" align=\"aligncenter\" width=\"350\"]<img class=\"wp-image-312\" src=\"https:\/\/opentextbc.ca\/accessibilitytoolkit\/wp-content\/uploads\/sites\/336\/2021\/02\/Progamable-thermostat-scaled-1.jpg\" alt=\"An electronic thermostat with a touch screen attached to the wall.\" width=\"350\" height=\"309\" \/> An example of a programmable thermostat.[\/caption]","rendered":"<p>Click play on the following audio player to listen along as you read this section.<\/p>\n<p><iframe loading=\"lazy\" id=\"kaltura_player\" title=\"2.9 Low-Voltage Thermostats\" src=\"https:\/\/api.ca.kaltura.com\/p\/148\/sp\/14800\/embedIframeJs\/uiconf_id\/23449753\/partner_id\/148?iframeembed=true&#38;playerId=kaltura_player&#38;entry_id=0_lqw37bvr&#38;flashvars[leadWithHTML5]=true&#38;flashvars[streamerType]=auto&#38;flashvars[localizationCode]=en&#38;flashvars[sideBarContainer.plugin]=true&#38;flashvars[sideBarContainer.position]=left&#38;flashvars[sideBarContainer.clickToClose]=true&#38;flashvars[chapters.plugin]=true&#38;flashvars[chapters.layout]=vertical&#38;flashvars[chapters.thumbnailRotator]=false&#38;flashvars[streamSelector.plugin]=true&#38;flashvars[EmbedPlayer.SpinnerTarget]=videoHolder&#38;flashvars[dualScreen.plugin]=true&#38;flashvars[Kaltura.addCrossoriginToIframe]=true&#38;wid=0_750vi0x8\" width=\"608\" height=\"80\" allowfullscreen=\"allowfullscreen\" sandbox=\"allow-downloads allow-forms allow-same-origin allow-scripts allow-top-navigation allow-pointer-lock allow-popups allow-modals allow-orientation-lock allow-popups-to-escape-sandbox allow-presentation allow-top-navigation-by-user-activation\" frameborder=\"0\"><\/iframe><\/p>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_230\">Low-voltage thermostats<\/a><\/strong> are smaller and cheaper to install and maintain, and the wiring does not need to have as high a voltage and power rating as their line-voltage counterparts. This is why <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_229\">low-voltage control circuits<\/a><\/strong> are favoured for central heating units. Low voltage thermostats are also more sensitive to changes in heat than line-voltage thermostats, and so can provide more precise control.<\/p>\n<p>When controlling a single large heating unit, such as a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_136\">central gas furnace<\/a><\/strong> or <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_137\">electric furnace<\/a><\/strong>, there is no zone control as with baseboard heaters; either the whole house is getting heated, or none of it is. A low-voltage thermostat installed in a central location, and powered by a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_138\">120 - 24V transformer<\/a><\/strong>, can senses the ambient temperature and be used to control a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_139\"><strong>relay<\/strong><\/a> to deliver power to the heating load.<\/p>\n<p>By using an <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_204\">extra-low-voltage<\/a><\/strong> source for the control circuit we get the benefit of lower cost and easier installation along with increased safety, allowing a simple two-wire low-voltage cable to be installed in an ideal location in the house. Because it is only meant to handle the control current and not the load current, low-voltage thermostats are highly responsive and can provide more accurate control than line-line voltage thermostats.<\/p>\n<p>Some models of low-voltage thermostats used to control central gas furnace or electric furnace loads incorporating heat exchanges and blowers, will have a small, series connected, resistive device called an <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_206\">anticipator resistor<\/a><\/strong>. The purpose of this device is to fine tune the sensitivity of the thermostat and prevent overshoot of the desired room temperature.<\/p>\n<p>Low-voltage thermostats, fall into two general categories, some are simple temperature activated switches while others are more modern <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_46_225\"><strong>electronic thermostats<\/strong><\/a> incorporating solid-state circuitry and allowing for programmable behaviours such as 24-hour cycles, and weekday vs weekend scheduling.<\/p>\n<p>Electronic thermostats use semiconductor components for both temperature sensing and control-circuit switching. If installed to replace an existing analogue thermostat, the electronic thermostat must have a separate power source, which is usually a battery.<\/p>\n<figure id=\"attachment_312\" aria-describedby=\"caption-attachment-312\" style=\"width: 350px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-312\" src=\"https:\/\/opentextbc.ca\/accessibilitytoolkit\/wp-content\/uploads\/sites\/336\/2021\/02\/Progamable-thermostat-scaled-1.jpg\" alt=\"An electronic thermostat with a touch screen attached to the wall.\" width=\"350\" height=\"309\" \/><figcaption id=\"caption-attachment-312\" class=\"wp-caption-text\">An example of a programmable thermostat.<\/figcaption><\/figure>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_46_230\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_230\"><div tabindex=\"-1\"><p>A temperature-activated switch that operates below 30V.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_229\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_229\"><div tabindex=\"-1\"><p>A control circuit which operates below 30V.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_136\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_136\"><div tabindex=\"-1\"><p>Main unit that converts natural gas into heat via heat exchanger and usually includes a blower motor.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_137\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_137\"><div tabindex=\"-1\"><p>Main unit that converts electrical energy into heat via resistive coils and usually includes a blower motor.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_138\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_138\"><div tabindex=\"-1\"><p>Often called a \u201cdoorbell\u201d transformer, this device converts the line voltage of 120V found in most AC circuits into an extra-low-voltage value of 24V which powers the control circuit.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_139\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_139\"><div tabindex=\"-1\"><p>An electromechanical switch that can be opened or closed remotely by small sources of voltage.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_204\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_204\"><div tabindex=\"-1\"><p>Any voltage not exceeding 30V. Equipment energized at 24 V is commonly referred to as the \"low voltage circuit\".<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_206\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_206\"><div tabindex=\"-1\"><p>A resistor that is physically mounted inside a room thermostat, and any heat generated by it will directly affect the temperature-sensitive bi metallic strip inside the thermostat.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_46_225\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_46_225\"><div tabindex=\"-1\"><p>A thermostat with a programmable feature.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":90,"menu_order":3,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-46","chapter","type-chapter","status-publish","hentry"],"part":37,"_links":{"self":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/46","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/users\/90"}],"version-history":[{"count":3,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/46\/revisions"}],"predecessor-version":[{"id":335,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/46\/revisions\/335"}],"part":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/parts\/37"}],"metadata":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapters\/46\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/media?parent=46"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/pressbooks\/v2\/chapter-type?post=46"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/contributor?post=46"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/opentextbc.ca\/basichvac\/wp-json\/wp\/v2\/license?post=46"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}