How To Make Your Basement Warmer

Thermal Imaging Camera
Thermal Imaging Camera. Getty / Banks Photos

Humans have long been burrowing underground as protection against intruders and elements.  It makes sense that we--today--seek partial protection in these dug-outs that we call basements.  The last thing anyone wants is a cold basement.  

These Things Help, But Not As Much As You Think

  • Insulating below-grade basement walls.
  • Installing basement sub-flooring or radiant heat floors.
  • Pumping in more heat.

Basement walls and flooring do play a part in making your basement cold, but only as accessories to the real culprit.  In proportion to the huge amount of square footage that walls and flooring take up, their roles are relatively minor.

Unless you are already finishing your basement, a simple cost-benefit analysis shows that pulling up flooring in order to put in sub-floor and ripping out below-grade walls to install insulation is not worth the work and expense.

Address Ground-Level Cold In Order To Warm Up Your Basement

Earth does a good job of regulating basement temperatures.  In terms of basement conditioning, temperate means that temperature ups and downs are not as pronounced as elsewhere in the house.  The highs are lower, the lows are higher.

Where does most of the cold come from then?  From ground level.

Ground-level cold is the real culprit.  It cascades into your basement through windows, ducts, vents, pipes, spaces around intrusions, the rim joist, header joist, and non-conditioned rooms.

Fix on-grade sources of cold and you have addressed a majority of the cold entry points into your basement--all without ripping out floors or walls.

1. Locate Cold Spots With Cheap Thermal Camera

If you are finishing your basement, viewing the interior with a thermal image camera is not just recommended--it is practically required.  

Thermal imaging cameras are no longer just for house inspectors and energy auditors.  Inexpensive mobile device add-ons, such as the Seek Thermal Camera or the Ryobi Phone Works Infrared Thermometer, pinpoint cold spots in your basement.  Results will surprise you.

This makes fall and winter the best times to finish your basement, at least from an energy-control standpoint.  This is the time when temperature spikes are at their greatest and are more visible on the thermal camera.

2.  Insulate Rim Joists and Headers

Your house's non-insulated rim joists and headers are probably the biggest offender.  

The rim joist is the last joist, the one that faces the exterior.  The header is the board that the joists are nailed into.  In older homes, both are left "as is," exposed to the elements.  

Cut 1.5" extruded foam insulation to fit these spaces and seal around the edges with a product like Great Stuff Gaps & Cracks foam sealant.

3.  Insulate Ducts That Enter/Leave The Basement

Ducts are unimpeded "freeways" that shoot cold air straight into your basement.  Dryer and bathroom fan ducts--mere tubes of thin aluminum or paper-thin plastic--provide zero insulation from the cold.  

Replace your current duct with an inexpensive insulated dryer duct or cover your existing duct with insulation.

4.  Install Better Vent Flaps

Most vents (the places where the duct leaves the house) are ridiculously terrible at preventing cold from migrating into your house.  Little more than a thin plastic door, these vents let cold air pour into the duct, and thus into your house.

Replace your cheap, ineffective vent flat with an energy saving "floating shuttle" type of vent flap.

5.  Insulate Basement Walls That Are Not Covered By Earth

Exterior basement walls that have earth mounded up against them do a fairly good job of preventing cold from coming into the basement.  Earth, after all, is a good natural insulator.

Basement walls that are not protected by earth--such as those found in daylight basements--are just as susceptible to cold migration as walls elsewhere in the house.  

Concrete walls must be insulated with extruded foam.  Wood-framed walls can be insulated with fiberglass batt insulation.

6.  Insulate Walls Of The Level Above The Basement

If you remember your basic science, you will know that cold air descends.  Non-insulated walls in the floor above the basement act as conduits for cold air to move down towards the basement.  

Insulating an entire level's worth of walls is not the easiest way to cure basement cold.  Rather, when considering whether or not to insulate upper floors, keep in mind the fact that cold upper exterior walls can affect lower areas of your house.

7.  Block Some Basement Spaces And Leave Them Unheated

Rare is the basement that has no functional services, such as a furnace, water heater, and washer and dryer.  Unless you have a special need for them to be heated, it is relatively easy to erect insulated interior walls that block them off, preserving heat for the basement areas that are inhabited.

8.  Insulate Basement Ceiling Areas That Have Unheated Spaces Above

Rooms on ground level that are not heated will compromise your efforts to heat your basement.  Insulating the basement ceiling will hold in the basement heat, preventing it from migrating to the unheated space above.

9.  Pump In More Heat

Wasteful when used as the only method of keeping your basement warm, adding heat sources is necessary if you want to push basement temperatures higher.  

Upstairs levels benefit from passive heating sources, chiefly solar heat gain; the basement never will.