How to Temporarily Heat a Structure During Construction

We are just coming into the heating season (lucky us).  If you live in a northern climate and you’ve made a career out of construction, or even if you’re a do-it-yourselfer, you may need to temporarily heat a space your working in.  In this post, I’m going to discuss several different heating fuels, the amount of heat they can provide along with current costs, and how the choice of the temporary heating system can affect a building.

For years I used fuel oil as a temporary heat source for many of the wintertime builds. Torpedo heaters put out a lot of heat in a short amount of time. The one I used the most was a 100,000 BTU thermostatically controlled unit that would hold around 5 gallons of fuel. The only good thing about this heater was the amount of heat it put out. The drawbacks were the amount of noise it created. It sounds like a jet engine taking off. It stinks, the burning of the fuel oil created an odor within the building. You had to fill the unit outside. If there was a fuel spill in the home, I’m not sure the smell of diesel fuel would ever leave if it soaked into the building materials. They were fairly expensive to operate. At 100,000 BTU’s, my heater would go through nearly a gallon an hour costing $4 per hour at current prices. And the most important factor, the exhaust of the burned fuel is vented directly into the structure, effecting the humidity and air quality inside the home.

I’ve also used unvented propane heaters as a temp heat source. I had both a torpedo heater and a radiant open flame space heater. Though they were cheaper to operate, around $2.50 per 100,000 BTU’s, they still had similar problems to the fuel oil heat.  Odors, noise and the risk of carbon monoxide. On top of that, there is the moisture issue. With propane, every 100,000 BTUs produced, around 1 gallon of moisture is released into the home. Natural gas produces even more at 1.25 gallons. Keeping a home as dry as possible during the construction process is important. Dehumidification will almost always be required while finishing the interior.

The concreteless slab on grade home that I was involved with a few years ago, the heat source used was electric. There were two different electric space heaters in operation. The first is a larger electric heater with two settings, 5000 watts and 3300 watts. We operated the heater on the 3300-watt setting only at night. During the day, a smaller 1500-watt heater was used. They are much quieter than the forced air torpedo heaters, no odors and the biggest advantage, no moisture load added to the structure. The disadvantage is the cost. Electricity rates in the area are around $.14 per kW. At 3300 watts, or 3.3 kW, the cost per hour is a little over $.45. Cheaper to operate on this job than the other sources I listed, but with a much lower heat output. 3.3 kW produces around 11,250 BTU.  We would need 9 times that amount to equal the heat output for the larger gas heaters, increasing the cost to $4.00 per hour, roughly the same as the fuel oil heater.  Luckily the home has a low heat need and the amount of heat the electric heaters are producing is more than enough.  (Another advantage to building well insulated and tight homes.)

Another good option for temp heat is an indirect heating system.  With this type of heat, the heat system is kept outside the building envelope and a duct is used to move only the heat produced by the system inside.  Combustion takes place outside, no combustion gasses, no odors, no moisture, and less noise.

How much heat can the more common heating fuels produce? Fuel oil produces the most BTUs per gallon at around 130,000 BTU. Natural gas is next at 100,000 per therm. Propane has around 92,000 BTU per gallon and electricity produces 3412 BTU per kW.  I have written a blog that talks about heat output and costs of different heating fuels. Read that blog post here.  (An older post with outdated fuel costs, but still has useful information.)

Why not use the permanent heat source to heat the home during construction? We can if it is a radiant heat source (no moving air), forced air systems contain ductwork.  We do not want construction dust and debris to accumulate inside the duct system during construction.

A quick note about unvented gas fireplaces and wall hung heaters. Don’t use them! I have run into these heating systems used as a primary heat source for a home. They rely on sensors to alert a homeowner when there is a problem with combustion in the unit. Incomplete combustion creates indoor air quality problems and can possibly place enough carbon monoxide in the air to cause health concerns and possibly death. They also release moisture into the home which can have a detrimental effect on the durability of the home.  Most gas suppliers in my area will not hook their gas supply lines to these units, homeowners or possibly untrained persons may be connecting the heaters to the gas supply. Not something I would leave to the unqualified person.

Temp heat is often a necessity to keep the construction process moving during cold weather.  The choice of the heat source can affect not only the workers inside the structure, but also the structure itself.  Choose wisely!