Used to be, contractors in northern climates would shut down operations during the winter, perhaps even grab a Florida vacation during the downtime.
Try telling a client today that you won’t be working on his project for three months. While there are times when winter shut-downs are necessary, total work stoppage for weeks on end have become rare. If you don’t work in the winter, you can bet your competition will.
And so you rent heat, lots of heat. You heat your workers, you heat your concrete pours and you heat your equipment. Heck, you can now even melt the frost out of the ground before you excavate. The increasing emphasis on winter production has meant that heat has become a big business for northern rental dealers.
“Every summer we have Winter Revenue Summits,” says Mike MacDonald, Northeast regional vice president, United Rentals. “It’s a kind of brainstorming session about what worked last year, and what everyone thinks we ought to try this year. In addition to heaters, we talk about tarps, blankets, snow removal equipment. It’s grown significantly each year. Winter revenue is a major part of our business now.”
For the most part, heaters found on the average construction site are of the forced-air variety. While other heaters are available – including convection, electric and radiant heaters – because of their generally low prices, users tend to purchase rather than rent these units.
That doesn’t mean your choices are limited with forced-air heaters. In fact, there are now more rental choices than ever. Which will be best for your job will depend on a number of factors, all of which you’ll need to discuss with your rental dealer.
Direct or indirect?
First, though, you’ll need to be aware of the two major categories of forced-air heaters: direct-fired and indirect-fired.
On direct-fired units, outside air is forced over ignited fuel, heating the air. With indirect-fired heaters, a heat exchanger and ducting are used to direct the heated air.
“Direct-fired heaters are typically put into a building that just has the walls up or contractors are just doing the foundation or grade beams on a building,” says Wade Dimock, branch manager of the Hertz Equipment branch in Edmonton, Canada. “You don’t want to use these heaters in an application where the building is tight. When you get the windows and doors in, that’s typically when you’d move to an indirect-fired unit.”
And there are other issues with direct-fired units, particularly since each of the products of combustion – moisture, carbon dioxide and carbon monoxide – are present,” says John Walsh, president of Heat Wagon. Moisture can be unwelcome, especially when drywalling. Carbon dioxide can play havoc with new concrete, creating a chemical reaction that causes carbonization, or chalking. And then there’s the obvious health hazard to humans when carbon monoxide levels get too high.
Be aware that in certain areas there may be local fire marshal bans on indoor use of direct-fired heaters because they involve an open flame. “The local fire marshal has a big say on what you can and can’t do,” says Bill Patterson, sales manager, North America, with Flagro Industries. “Some are very strict on what can and cannot be used for temporary heating, including areas of Massachusetts, Maine and New York City. But like any piece of machinery, they’re safe when they’re used properly.”
Indirect-fired heaters take the forefront when the building gets tighter. “The indirect-fired heater is the premium heater used when everything needs to be right because it’s more like a home furnace,” says George Stoneback, director of sales and marketing, Universal (a Scheu Manufacturing company). “We’ve seen a tremendous growth in indirect-fired heaters.”
“Indirect-fired heaters used to be used on just larger buildings,” Patterson says. “Now you can rent relatively inexpensive indirect-fired heaters.”
There’s still a significant difference in the rental rates between direct-fired and indirect-fired units, says Doug Dahlgren, product manager, Allmand Bros. And rental rates for all types of temporary heat need to be fairly steep in the first place since the rental store only has roughly four months to recoup its investment.
Contractors are familiar with direct-fired units, which offer dependable heat.
The new kid on the block: Hydronic heaters
“One of the biggest things you have to consider is the cost of the fuel,” MacDonald says. “The rental of the product pales in comparison with the cost of the fuel.”
This has led United Rentals to promote rental of one of its newest winter products, hydronic heaters. “The biggest feature is the fuel efficiency,” MacDonald says. “People have been able to cut their fuel bills in half with this heater.”
Hydronic heat, which has been in the market about three years, delivers heat through a process similar to that used to thaw ground. “With a hydronic air heater, the heater heats the fluid, which a pump then circulates through a hose to a liquid-to-air heat exchanger,” says Sue Meekhof, vice president of sales for western North America for Ground Heaters. The heat exchanger’s fan then blows air across the heating coils, and warm, dry, clean air flows out into the workspace. The fluid then returns to the heater for reheating.
Hydronic heaters offer dry heat, avoiding the problems of moisture that are inherent with direct-fired heaters. “This type of heat has really grown in popularity because of the problems contractors are experiencing with moisture and mold,” Meekhof says.
“Mold is becoming a major issue in the Northeast,” adds MacDonald. “Both hydronic and indirect-fired heaters are excellent in combating mold.”
“These heaters are just coming to our area,” Dimock says, “and we’re looking to do big things with them. We’ve got a lot of walk-up apartment building projects, and contractors will be able to have a heater on each floor, driven by one unit on the ground.”
Dimock also is aware there are safety advantages with hydronic heaters over direct-fired heaters. “In northern Alberta a condominium was lost that was nearly complete when a contractor left a direct-fired heater running all night near flammable materials. Contractors are always looking for a safer way.”
As with all heater types, it’s not a one-machine-solves-all-problems unit, warns MacDonald. “It’s not for everything,” he says. “For instance, you probably wouldn’t use it in a skyscraper that’s wide open.”
Fuel choices
When selecting which heater to rent, you should also consider both fuel selection and cost. For example, fuel costs of $300 a day are not unusual – and you need to figure it as an additional cost on top of the rental rate.
These heaters use a variety of fuels, including natural gas, liquid propane, vapor-propane, kerosene and diesel. Location also plays a big role in fuel selection and what type of fuel your rented heater will require.
“Rental dealers should be asking contractors what fuel sources they have available,” Patterson says. “Is the jobsite already set up with natural gas? In some areas, such as places in New Hampshire, they don’t have natural gas, so they have to use propane.”
And keep in mind some fuels used in direct-fired heaters can present problems. “Propane and natural gas are a bit more cleaner burning than diesel or kerosene, which tend to produce both a smell and a fuel mist if they don’t burn properly,” Patterson says. “That can get onto the drywall or concrete and cause a problem.”
Other job considerations
“Rental dealers should be asking how big of an area you are going to heat up so they can calculate the BTUs,” says Fernando del Aguila, president, Volvo Rents, Kingston, New York. All rental places should have these formulas close at hand. If they don’t, perhaps you should look for another source of rented heat.
In making these calculations, rental dealers will also have to consider the type of building under construction: multi-story building or a single level? Is it an uninsulated steel, cement block or wood frame building? All are factors in determining the amount of BTUs needed. “This is not a real precise science because you’re usually heating a structure with lots of holes in it,” Patterson says.
Your rental dealer also should know how airtight the building is. “Is it new construction that’s all tarped in?” Dimock asks. “We use insulated blankets up here where 10 to 15 years ago they would wrap a building up in poly, which is just enough to block the wind. These insulated blankets have about a R5 to R8 insulation value and so the buildings are getting tighter and tighter.”
Heaters are rated by BTU input values. You should be interested in the net BTUs rather than the gross BTUs, according to Meekhof. While gross BTU numbers allow you to determine how much fuel is consumed, net BTUs will tell the story on heat delivery, or the actual heat you get to use.
Hydronic air heaters are the newest rental choice and offer significant fuel cost savings.
Most construction-type heaters would range from 400,000 BTUs to 7 million BTUs, according to Walsh. Heaters also come with different electrical power requirements. Some heaters require 110 volts; others can require up to 480-volt, three-phase electricity.
Your dealer should ask you about the amount of temperature rise you’ll require – or how much higher than the ambient temperature you want the heat to rise. In a working environment 50 to 60 degrees is usually sufficient, allowing workers to work in sweatshirts. So for an ambient temperature of 35 degrees, you’ll just want to raise the temperature by 15 to 25 degrees. “That’s how you size the job,” Walsh says.
Still, the term “adequate heat” depends on the type of work being done, Dahlgren says. “Your rental dealer should always ask you what temperature you want to maintain in the work environment. They should also know the number of people, if any, involved.”
When using direct- or indirect-fired heaters, you and your rental dealer should also consider how many auxiliary fans you’ll need to enhance the circulation of the heater. “The advantages of forced air is that it does assist in circulating the air, so you get better distribution of the heated air in the environment,” Stoneback says.
You still need to make sure you have fans inside the building to just keep the air moving, Dimock says. “Each heater has a fan to drive it,” he says, “but heat tends to layer, so put the fans up as high as you can or even on the floor angled up to get the heat moving in a cycle pattern. Typically, 20-inch fans are used for this.”
“You don’t need a heater in every room; as long as you have open doorways and walls, it will circulate throughout the building,” Walsh says.
Errors in heating
When you ask these experts about common jobsite mistakes with rented heat, the number one error cited is a failure by the contractor to plan for jobsite heat. This can even lead to a situation where you have to pay a premium because the local heater supply has been depleted.
“Especially on some of the smaller jobs, contractors wait until it starts to get cold, and there’s a definite lack of planning,” Patterson says. “This may lead to them having to take a product that’s not the best for their situation.” And even though winter always happens, some winters in the past few years have been relatively mild, causing contractors to hesitate further.
A lot of contractors look at temporary heat as an insurance policy, Walsh says. “In the early fall they meet with their rental dealer and get a plan set up for temporary heating on a job, with the layout of the heaters.”
“We try to get contractors to sign up for their temporary heat needs before winter,” MacDonald says. “We basically have a whole package and we’ll give them a 20 percent discount if they rent for the four-month season and pre-pay.”
Other frequent problems include:
Power problems. “Eighty percent of our service calls are for power reasons,” Dimock says. “A lot of construction sites just don’t have the power to run these heaters. You need to be aware that they can’t get away with the same extension cord you use to light up your Christmas tree. All our heaters go out with a 10/3 heavily insulated extension cord that’s about the thickness of your thumb. For the bigger heaters, you need a dedicated 20-amp circuit. If you’re not getting enough power, the heater starts cycling on and off.”
Propane quirks. While it’s a valued clean-burning fuel source, propane does have its eccentricities. “Customers do sometimes have a problem understanding what the rate of evaporation is with propane,” says del Aguila.
“With propane, when it gets really cold, you need a vaporizer in your line,” Dimock says, “especially for the bigger heaters. Since propane can only burn as a gas, the vaporizer will turn liquid propane into a vapor as it heats up.”
Air flow. Make sure you have sufficient ventilation throughout the area being heated, especially when using direct-flow units.
Amount and placement of ducting. Indirect-fired heaters typically use ducting to distribute the heated air. The maximum ducting distance will be determined by the static pressure capability of the fan, Dahlgren says. For best performance, Dahlgren recommends using the minimum amount of ducting possible, since ducting is typically not insulated and is somewhat restrictive to the airflow. Short duct runs result in less heat loss through the duct and an overall more efficient use of the heat produced.
“You’ve got to make sure you have straight runs,” Dimock says. “If you have to bend it two 90 degree turns that’s too many. You’ll have to find a more direct way.”
Sensitivity to altitude. The higher you go, the less fuel you’ll be able to burn because there’s less oxygen. You’ll need to make adjustments to the heater to get it to operate efficiently.
Another consideration: Buying heat. Also consider that maybe the most economical way to get heat in the long term is to buy it, not rent it.
“If the contractor needs to rent the heater for more than a season, I think they’re better off buying,” Patterson says. “The prices have come down on even big heaters.”
