Reducing Energy Losses
There are three basic types of gas-fired tap water heating systems: conventional water heaters that heat the water directly in a tank; instantaneous heaters without a tank that heat the water only when it is being used; and systems that heat the water in conjunction with another energy use, usually for space heating. For the latter, it can be in the form of a "tankless coil" inside the boiler or a storage tank tied to the boiler through an efficient water-to-water heat exchanger.
The operating efficiency of a domestic hot water system can be improved significantly by carefully designing the system. Selecting equipment that generates the hot water more efficiently reduces stack and standby losses. Modifying an existing system, including piping modifications, can also reduce some of the standby losses.
Reducing Standby Losses
The term "standby loss" refers to heat lost from the water in a domestic water heater and its distribution system to the surrounding air. It is a function of the temperature difference between the water and the surrounding air, the surface area of the tank, and the amount of insulation encasing the tank.
You should consider the following options to reduce standby losses:
- Insulate the tank with an approved insulating blanket.
It is extremely important not to insulate over any controls or obstruct the vent connections or combustion air openings. Furthermore, the insulation should not come in contact with the vent connector.
- Install a heat trap above the water heater. A heat trap is a simple piping arrangement that prevents hot water from rising in the pipes, thereby minimizing the potential for this loss.
- Insulate the hot water pipes to reduce heat loss from the pipes themselves. Pipe insulation is available in a variety of materials and thicknesses, with easy application to most hot water pipes. Use insulation with an RSI (insulation value) of at least 0.35 (R-2) over as much of the pipe as you can easily access.