Who said you can't dig foundations during the winter?
Many contractors in northern climates stick to inside work during winter because digging and pouring a foundation can be hopeless if large areas of ground are frozen. In addition, pouring concrete over frozen ground can lead to big structural issues when the ground thaws.
Enter ground heaters. Part electric blanket and part mobile radiator, these units make the ground forgiving enough for contractors to carry out excavation and foundation work in winter.
The most effective ground heaters are hydronic and use propylene, water and glycol-filled rubber hoses to warm whatever surface they're placed on. A typical unit consists of a portable fuel-fed boiler and pump, in addition to the hoses. With hydronic ground heaters, 93 percent of the heat finds its way to the ground or other surface compared with only about 15 percent with air heaters.
There are three main uses for a ground heater on a construction site.
Remove ground frost
To remove ground frost, ground heater hoses are placed directly on the soil, covered by a vapor barrier and then covered once more by insulating blankets. This method can thaw approximately 6 inches of frost every 24 hours, which translates to the elimination of about 4 feet of frost in just over a week. It's not an overnight fix, but it beats waiting for spring.
After a pour, concrete must be allowed to cure. That process is interrupted if the concrete freezes. In fact, freezing can reduce concrete strength by up to 50 percent.
To prevent this, a ground heating system is placed underneath the pour location to raise the ground heat to between 85 and 90 degrees. Once the ground temperature is at an acceptable level, the heating system is removed. After the pour, the system can be used to maintain the concrete's temperature until it has reached the specified required strength.
Create warm air
Finally, ground heating systems can be used to create warm ambient air for workers in small enclosures or well-insulated and dried-in areas of the job. The hoses that would typically be laid on the ground or on top of concrete are connected to a portable heat exchanger or fan coil. Air is then blown across the heated coil and into either a single space or, using a setup of several heat exchangers, multiple spaces.
Kim Slowey is a writer who has been active in the construction industry for 25 years and is licensed as a certified general contractor in Florida. She received her BA in Mass Communications/Journalism from the University of South Florida and has experience in both commercial and residential construction.