Heaters are hired on two numbers: output in BTU per hour, and whether the flame sits in the air you are breathing. A direct fired torpedo between 100,000 and 400,000 BTU costs roughly $60 to $120 a day. An indirect fired unit, which vents combustion outside and blows clean warm air down a duct, starts nearer $150 a day.
Direct or indirect is the first decision
A direct fired heater puts its exhaust and a good deal of water vapour into the space, which is acceptable in open framing with real ventilation and wrong anywhere sealed or occupied. An indirect fired unit keeps combustion in a heat exchanger vented outdoors, so the air it delivers is dry and clean. Finishing, curing and occupied work needs the indirect machine.
Sizing without over ordering
Output follows the volume of the space, how cold it is outside, and how leaky the building envelope still is. Give the yard the dimensions and the state of the walls rather than guessing a number. Two medium heaters placed apart usually beat one large one, because heat that all arrives in one corner leaves the far end cold.
Fuel is the running cost, not the rental
Propane, diesel and kerosene units burn steadily at full output, and a large propane heater will empty a hundred pound cylinder faster than anyone expects. Settle who supplies the fuel, who swaps the cylinders and whether the tank returns full, because on a long cold week the fuel line exceeds the hire line.
Carbon monoxide is the risk that kills
Every fuel burning heater produces carbon monoxide, and an unvented one in a space that has been closed up for winter is the classic fatal combination. Ventilate to the manufacturer requirement, put a monitor in the space, and never run a direct fired heater in a basement or a sealed room to save the cost of the indirect unit.
Questions people ask about construction heater rental
Can a construction heater run overnight?
Indirect fired units with a thermostat routinely do, and that is how slabs and finishes are held above freezing. An unattended direct fired heater in a partly sealed building is a different matter and many sites prohibit it. Check fuel capacity for the number of hours, and confirm what the yard says about unattended running.
What size heater dries out a slab or a flooded room?
Heat alone raises the air temperature and the humidity with it. Drying needs warm air, air movement and something removing the moisture, which means pairing a heater with fans and a dehumidifier from the same counter. Ask for the drying package rather than a bigger heater.
Do electric heaters need a generator?
Small fan heaters run on ordinary circuits. Anything giving real output electrically wants a heavy single or three phase supply, and on a site without power that means a generator sized for the load with headroom. Even fuel fired heaters need power for the fan, so a temporary supply is part of the hire.