"Curing" the winter blues Seattle WA

Portable hydronic heaters were originally introduced about 12 years ago to the construction market as ground thawing equipment. They were designed to help contractors stay busy through the frozen winter months by taking the frost out of the ground. But industrious contractors soon learned that hydronic heaters could be used to allow concrete pouring through winter as well.

As concrete cures, it puts out heat. The warmer the concrete, the faster it cures. When it's frozen or very cold, concrete can stop curing altogether.

According to the American Concrete Institute (ACI), concrete placed at or below 42 degrees must have heat protection for a proper cure. So contractors don't have many choices during the cold months of winter: protect the pour, use additives or don't work.

There are various methods for protecting a concrete pour, including concrete insulation blankets, propane heaters with tents, etc. There's also portable hydronic heating systems, which are designed to help keep concrete pours at their ideal curing temperature — 65 to 75 degrees F.

Keeping a concrete pour at its proper temperature during the curing process not only speeds up how fast it cures, it also helps the concrete develop strength in a shorter amount of time. Simply put, cold temperatures slow the speed of the concrete's cure, which increases cost and causes schedule delays for your customers.

Hydronic heating systems can thaw ground and cure concrete in a fraction of the time of traditional direct- or indirect-fired gas heaters. Not only does this help contractors to more accurately quote and plan their jobs, it also allows little downtime for their crews and equipment, which equals further savings.

"To put it simply, hydronic heaters help contractors take the unknown factor of weather out of the picture," says Ken Cannella with Ground Heaters.

How it works

There are a few different hydronic heating systems available on the market today. While each system is unique, the concept is generally the same and pretty simple.

For example, during a thawing application, the unit's boiler heats a propylene glycol mixture and pump the warm fluid through the long loops of the heater hose, which are generally laid out 12 to 24 inches apart on the area to be heated.

Propylene glycol is like a food-grade anti-freeze that effectively conducts heat. The hoses are then covered with a vapor barrier, which helps prevent water vapor from escaping the thaw area.

On top of the vapor barrier, insulation blankets are placed. The combination of these two is to keep the energy in the ground, changing the ice to water and further accelerate thawing. As opposed to 15 percent of heat directed into the ground using air heaters, 93 percent of the heat is conducted into the ground using hydronic heaters. (This percentage can vary depending on the use of a vapor barrier and number of blankets.)

The goal of each heater during the concrete curing process is as simple as the technology that runs it: to keep the pour at an ideal, constant temperature so the concrete can cure properly. In the case of a slab, the heater can also be used initially to heat the ground to give the concrete pour a warm base to start.

The setup of a heater system varies depending on the type of pour your customer would be doing. For example, when pouring a slab, the ground needs to be preheated first. Fluid in the system in preheated to about 180 degrees, which helps the ground reach a temperature of about 85 to 90 degrees. Then the hoses are placed at 24-inch centers, insulating blankets are placed and the ground is warmed. After removing the heating system and blankets, the concrete is poured.

When the concrete is set, the vapor barrier, hydronic hose (with 24-inch spacing) and insulation blanket are placed. The heating system temperature should be reduced to 120 degrees F and controlled, so the outgoing temperature of the glycol mixture stays in a 65- to 75-degree range. The heat will need to be maintained until the concrete has reached its desired strength. This usually takes three to seven days, depending on the ambient temperature.

Portable hydronic heaters can be used on various types of concrete placements, including tilt-up concrete construction, slab-on grade, poured walls, columns and elevated placements, such as bridge decks and multi-story buildings. They can also use hydronic heaters to heat rebar before pouring.

And these units can be used for more than just concrete applications. As Chuck Porter with Thawzall says, "The more people use this technology, the more ideas they come up with to use it in other ways."

Other applications include ground thawing, pipeline maintenance, temporary structure heating and environmental applications, such as removing hydrocarbons from soil. For more unique applications, see the box, "What will they think of next?"

Purchase considerations

The initial investment for these machines is not cheap. Depending on the size and accessories, they can run from the $20,000 to over $60,000. Of course, rental rates are not on the light side either.

"Rental rates are pretty decent for these machines considering there's only a four- to five-month window each year to rent them out," says Cannella. "Rental businesses can expect to get — depending on the size of the machine and accessories — between $5,000 and $9,000 a month."

In addition to the sticker price of the equipment, you should take a close look at your market before purchasing hydronic heaters for your rental inventory. Here are some items to consider:

• How long is the winter season in your area?
• How deep does the frost typically get?
• Do other rental centers in the market rent this type of equipment? If so, how price sensitive is the market? If not, are you willing to pioneer a new product in the market?
• What are your service capabilities? Does the manufacturer offer training for your sales and service personnel?
• Do you rent equipment used to prepare for concrete placement?
• Would including a cold weather product in your inventory add value and bring in extra revenue for your business during this quarter of the year?

Units vary in their capacities for curing concrete. The range extends from 1,100 square feet up to 50,000 square feet per application.

As far as thickness of the pour, it really doesn't matter. Concrete generates its own heat when curing, so the hydronic heater just protects the concrete from freezing.

As far as thawing ground, depending on soil conditions, most hydronic heaters can remove frost from the ground at a rate of one foot per day for the first three feet, than 1/2 foot per day thereafter.

"One of the benefits with this technology is 93 percent of the energy being produced by this machine goes directly to the source you want to thaw," says Porter. "This eliminates excessive propane expenses as well as man hours, because no temporary shelters have to be built."