Straight Talk Articles
Are Outbuildings Worth Heating or Insulating?
Dear Pat and Brad:
We just purchased a house and noticed that the previous owner installed an electric wall heater in a shed in the back yard. How much will our electric bill go up if we use this heater all winter? Should we insulate the shed? – Lloyd
Good questions! An uninsulated outbuilding can be very expensive to heat depending on where you live. Years ago I worked on an energy contest that picked out homes with the biggest energy bills and helped the owners make efficiency improvements. One year the home with the highest energy use had an uninsulated shed that was heated in order to keep several cans of leftover paint from freezing. The cost of heating the shed each winter was more than it would have cost to replace the paint.
How much it will cost to heat your shed or outbuilding depends on your climate, the thermostat setting for your wall heater, the size of the outbuilding and the price you pay for electricity. We did a simple heat loss calculation of our own that showed heating an uninsulated 6 foot by 8 foot shed could cost twice as much as heating a 900 square foot home that is insulated to typical levels(1).
Some shop buildings are heated with wood, which is a sound choice if you have a free source of firewood. Another strategy often seen in workshops is a radiant heater directed at the work area, in front of a workbench perhaps. But if you’re paying for your fuel and decide to keep an outbuilding heated you should definitely insulate it.
An important consideration, unless you live in a desert-dry climate, is the effect moisture can have in an outbuilding, whether or not it’s heated or insulated. Moisture enables rot, insects and mold to wreak havoc on your structure(2) and rust to degrade tools and other metal.(3) Heating and insulating an outbuilding, if it’s done right, can reduce or eliminate a moisture problem. Insulation installed incorrectly, however, can trap moisture and foster mold growth.
Moisture in an outbuilding is usually caused by 3 things: leaks where water can get through, usually through the roof, windows and doorway; seepage through floors and walls; or condensation when nighttime temperatures drop. To prevent moisture buildup, you need to eliminate moisture sources and prevent condensation.
As air cools it cannot carry as much moisture, and condensation occurs, usually on the coolest object at hand. Insulation in walls and ceilings can keep the interior wall or ceiling surface from getting cold enough for condensation to occur. Insulated wall or ceiling cavities need to be carefully air sealed so that condensation does not occur inside the cavity.
The cost of heating and cooling an outbuilding can be much lower if the thermostat is carefully controlled. Or you can divide the interior of the outbuilding with an insulated wall, and just heat or cool the part you use.
Only you can decide whether the value of heating and cooling your outbuilding is worth the cost of the fuel and the cost and effort to properly insulate and air-seal. If you decide not to heat or cool your outbuilding, you can prevent condensation by keeping the humidity and temperature the same as outside with screened vents in the walls. Whether or not your shed is heated or insulated, it’s worth keeping an eye out for mold and mildew.
We hope you enjoy your new home and your backyard shed – whether or not you decide to heat and insulate it!
This column was co-written by Pat Keegan and Brad Thiessen of Collaborative Efficiency. For more information on heating or cooling a backyard shed, go to the July 2021 more info page.
(1) Collaborative Efficiency calculation
Moist air in a shed or workshop can cause tools to rust. Source: Floris van Halm, Flickr.com