Garage Heating, From The Floor Up
As a kid, I grew up in as many places as my father's Navy career took me. When I was in the fifth grade, we lived in Bremerton, Wash., while my dad's submarine tender went through the shipyard for an overhaul.
Two of my fondest memories of that stay were trolling for trout at Lake Tiger and visiting a racing car garage located off the alley that ran behind my house.
I could stand for hours outside the garage door and watch the mechanics rebuild their midget racing car during the week as they got ready for the weekend race.
While I never thought about heating the place at that time in my life, I do think a lot about it now. Heating a garage is much different than heating a residential dwelling or a commercial office space. For one thing, opening a garage door, especially during windy conditions, can take all the warm air out of the space very quickly.
As you might have guessed already, radiant heat is an excellent way to heat such spaces. Using the floor as a giant radiator provides a huge "battery" of heat that allows quick recovery when the doors come down. Even with the doors up, the radiant floor continues to provide heat, much as the sun does on a windy day.
Since used oil is a standard feature of many garages, many businesses install waste oil boilers in addition to standard boilers as an energy choice. Including a snowmelt system makes a lot of sense especially when waste oil is present. At a minimum a snowmelt system should be installed in the pad outside the garage doors about 5 feet out. This helps keep the plows away from the garage doors. Also, if there are any ramps leading into the garage, a snowmelting system provides a safe entrance and exit area for the garage.
Heating RequirementsThe heating requirements for a garage depend on how the facility is to be used and constructed.
A garage can have many uses and these uses should predicate the design of the heating system. Garages that are used for vehicle maintenance could have their doors opened hourly. Garages that are used for repairing equipment could be opened daily. Garages that are used for storage, this could be monthly.
Working garages have a different comfort requirement than those used just for storage. It is very important to provide a working environment that allows dress that is not bulky, but at the same time provides some protection if the doors are coming up and down to service a vehicle.
When the door comes down, the garage must stay at some minimal temperature. Most working garages that operate between 60-65 degrees F are very pleasant to work in with the workers wearing two layers of clothing. The floor temperature should never go above 85 degrees F and should operate between 60-75 degrees F to provide the ultimate comfort. Colder floors take energy out of the worker. On the other hand, floors that are too warm might make the service guys working under the trucks fall asleep!
To prevent overheating of the garage from the floor heating system, the use of slab sensors works best. Garages used for repairing and storage can be heated with floor heat as the only source of heat. It is possible to control this type of application with a thermostat on the wall, but I still like the idea of a slab sensor better for temperature control and comfort.
Here are a few other common factors to keep in mind:
- Infiltration: A 10-minute oil change facility has large doors that come up and down every five minutes on average, allowing large quantities of outside air in. A maintenance garage for a utility or highway department opens the doors once or twice a day. A garage such as the NASCAR teams now have may only open the doors three or four times a week. The opening required for large garage doors and how well they are sealed when the door is closed can also be a source of infiltration that would be greater than usually experienced in a closed building.
- Exhaust Air: Garages that paint, run engines or use solvents require exhaust and makeup air ventilation. This ventilation also will remove heated air from a room. The heating system will be required to make up for this loss of heated air.
- Building Construction: Many garages are built either from concrete block or steel frame with aluminum siding. Concrete block construction can have poor insulation (low R-values) and high infiltration rates. Aluminum-sided buildings can also have the same. As a result, upgraded insulation should be considered an important feature for the design and construction of the garage. Garages that are being retrofitted should also address this important issue.
Garages are typically slab-on-grade. The use of insulation around the perimeter of the slab will greatly reduce the heating requirement for the space. Two inches of polystyrene insulation is recommended. Floor drainage in a garage is very important if the garage is being used to provide overnight storage for vehicles that return with snow and ice on them each day.
Real LifeYou can see how much of these conditions come into play for Rhoads Energy Corp.'s new 9,000-sq. ft. headquarters and service facility, in Lancaster, Pa.
A full-service energy company, Rhoads supplies homes and businesses in South-central Pennsylvania with heating oil, gasoline, diesel fuel, kerosene and electricity. The company also installs and services heating and cooling systems, humidifiers, water heaters and other related products.
At the time of this writing, Rhoads' new building was just a couple weeks away from completion. It is situated on a sloped, corner lot and consists of two floors. The street-level front entrance provides access to what is really the building's second floor, which offers 4,500 sq. ft. of office space. The first floor, or basement, is accessed from the back of the building and provides 4,500 sq. ft. of garage and warehouse space.
The five-bay garage will typically be used to house and service three Rhoads fuel oil trucks and a lift-gate body truck. The fifth bay will serve as a wash bay or as extra space for another truck. In addition, about 10 percent of the basement will be dedicated to warehouse space and a small break room.
The company went with baseboard heat for the second floor, but radiant for the garage. Rhoads is also taking advantage of radiant heating's snowmelting capabilities as well. The company has already installed radiant tubing in the 15-ft. concrete sidewalk approach to the building's front entrance. This will keep the sidewalk clear of ice and snow so customers can walk safely to and from the building. Radiant tubing will also be installed in an area spanning 5 feet out from the rear of the building. This will keep snow and ice away from the garage bay doors, thus avoiding snowplow damage to the building and allow trucks to enter and exit the garage safely.
To plan the system, Burnham considered the heating and snowmelting requirements of the project, then provided Rhoads with a tubing design layout. The design called for 16 radiant piping circuits, each averaging 310 ft. in length.
Once the building foundation was laid and the roof was up, the garage floor was graded and covered with stone. Eight, 4- by 125-foot rolls of poly double bubble foil barrier was placed over the stone and a 1-inch thick polystyrene insulation was installed to insulate the perimeter of the floor slab. A grid was formed from 6- by 6-inch wire mesh, to which 3/4-inch PEXc barrier pipe was then tied, forming the loops. A second grid was placed over the pipe for added strength to the floor. Six inches of concrete were poured over the entire area, with air testing being performed throughout the process.
For the snowmelting system, the same process was followed, and a brazed plate and frame heat exchanger was used. A built-in timer can be set to heat up more frequently as inclement outdoor conditions worsen, or less, as outdoor conditions improve.
One interesting aspect of the job was the installers -- Rhoads used its own employees. The company's technicians hooked all of the piping to a 1 1/4-inch, four-way mixing valve to mix water temperatures. A motor control mounted on the mixing valve provides heating water reset capabilities. Essentially, the control can sense when the inside temperature changes and adjust the water temperature going to the floor heating system to provide the ultimate in comfort and energy efficiency.
This controller is also the thermostat for the space. With the garage doors coming up and down, an outdoor temperature sensor is less responsive to the demands of the environment. The system will also use constant circulation, and the slab will have a sensor to close the mixing valve if the temperature of the slab goes over 85 degrees F.