On many occasions, I’ve had the chance to converse with bar and restaurant owners and national chain facility directors on the topic of the proper design of an outdoor patio heating system.
And almost just as often, I find them to be surprised when they hear what the real factors are.
In those discussions, I often hear comments like “need to hold in the heat” or “keep the air warm”. This would seem to indicate that there is belief out there that the containment of heat or keeping the air warm is the goal of an outdoor patio heating system, especially a patio outdoor heater. But in fact, these concepts are not a consideration in a proper design. Simply put, we do not want a system that depends on heating air around the patio occupants to achieve comfort simply because keeping warm air in an area that has limited or no barriers to the outdoors is extremely difficult if not impossible.
Proper outdoor patio heating system design is driven by three critical elements.
First is the need to heat objects directly. Directly heating objects such as people, chairs, table tops, etc. accomplishes the goal of occupant comfort while completely avoiding the problem of warm air containment. The easiest way to heat objects directly is through the use of infrared heat or more specifically infrared “beams”. Much like the sun’s rays, an infrared “beam” does not release it’s heat energy to the air it travels through but rather only on the solid objects it impinges upon. In our case (and as long as the “beams” are directed in the right places), these would be the people, chairs, table tops, etc.. What then remains to be determined is the:
Second critical element of our design and that is the size or heating capacity of our infrared system. Empirical data charts provide us the amount of heat (in BTU’s per square foot) required to keep occupants comfortable at a given surrounding outdoor temperature. Therefore, it is the size of the patio and at what minimum outdoor temperature we would like to operate the patio that will determine the heating capacity of our infrared system.
There is a third, and final critical element that can significantly impact our design and must be considered. It is the concept of “wind management”. The empirical data charts I spoke of do in reality take into consideration the element of sustained wind velocity. This means that the charts tell us the required BTU’s per square foot at a given outdoor temperature AND sustained wind velocity. More BTU’s per square foot are required for outdoor heat as the temperature drops and as the sustained wind velocity increases. The obvious reason for this is that lower surrounding temperatures and higher sustained wind velocities remove heat from our people and objects at a faster rate and this lost heat must be replaced.
So now with all factors considered, the capacity of our infrared system is determined by patio size at a given temperature and a given sustained wind velocity. Based on this, it clearly behooves us to lower the wind velocity factor through the use of “wind management”. It sounds fancy, but it’s simply the use of physical elements such as adjacent building structures, awning tops and vertical curtain panels as wind barriers. Contrary to what some believe, it is the ability of these physical elements to block the wind that is important to us and not their ability (or inability) to “hold in heat”. And since these elements affect the sustained wind velocity factor, they will have an affect on both the system design and ultimately its successful operation.
Dan Gonzalez is a recognized expert in outdoor heating with more than 20 years designing and installing heating systems.He is the President of Awning Sun, a company that designs, installs, and sells outdoor infrared heatng systems.