<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ce8d2-7af3-7697-8fbe-a56c54040710,g:dbf259b8-9aa7-460a-9682-7563ead59d21-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_lii_AlokMaskaraMember_019ce8d2-7af3-79fd-9c36-f6a12f0b3374" xlink:href="lii-20260406.xsd#lii_AlokMaskaraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lii_AlokMaskaraMember_019ce8d2-7af3-79fd-9c36-f6a12f0b3374" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_lii_ToddM.BluedornMember_019ce8d2-7af3-7248-80d2-37851902dd60" xlink:href="lii-20260406.xsd#lii_ToddM.BluedornMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lii_ToddM.BluedornMember_019ce8d2-7af3-7248-80d2-37851902dd60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_lii_ToddJ.TeskeMember_019ce8d2-7af3-7f0c-8217-d2bdd7d0a289" xlink:href="lii-20260406.xsd#lii_ToddJ.TeskeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_lii_ToddJ.TeskeMember_019ce8d2-7af3-7f0c-8217-d2bdd7d0a289" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#PvpAdjustmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllAdjToCompMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllAdjToCompMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_lii_AggregateGrantDateFairValueOfStockAwardAmountsReportedInSummaryCompensationTableMember_019ce8d2-7af3-7fc6-ba73-64bcf5781eef" xlink:href="lii-20260406.xsd#lii_AggregateGrantDateFairValueOfStockAwardAmountsReportedInSummaryCompensationTableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_lii_AggregateGrantDateFairValueOfStockAwardAmountsReportedInSummaryCompensationTableMember_019ce8d2-7af3-7fc6-ba73-64bcf5781eef" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_lii_AggregateGrantDateFairValueOfOptionAwardAmountsReportedInSummaryCompensationTableMember_019ce8d2-7af3-7d93-b2f6-bb848e6e3d91" xlink:href="lii-20260406.xsd#lii_AggregateGrantDateFairValueOfOptionAwardAmountsReportedInSummaryCompensationTableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllAdjToCompMember" xlink:to="loc_lii_AggregateGrantDateFairValueOfOptionAwardAmountsReportedInSummaryCompensationTableMember_019ce8d2-7af3-7d93-b2f6-bb848e6e3d91" xlink:type="arc" order="5"/>
  </link:definitionLink>
</link:linkbase>
