How are boilers rated?

How are boilers rated?

• A. Gross rating
• B. Thermal rating
• C. Efficiency rating
• D. Net rating

Answer: (D)

Boilers are rated by the net heat output they can deliver to the heating system. This net rating reflects the useful heat actually supplied after subtracting losses such as heat that goes up the vent and other system losses. It’s the most practical figure for sizing a boiler to meet a building’s load, because it shows how much heat you can rely on. The gross rating, by contrast, counts heat produced before losses, which overstates what reaches the living spaces. An efficiency rating is a separate measure of how effectively the fuel energy is converted to heat, not the amount of heat delivered. And the term thermal rating isn’t the standard way boilers are described in most catalogs. For example, a boiler might produce 1,200,000 BTU/hr gross, but deliver only about 1,000,000 BTU/hr to the system in net rating due to losses.

Boilers are rated by the net heat output they can deliver to the heating system. This net rating reflects the useful heat actually supplied after subtracting losses such as heat that goes up the vent and other system losses. It’s the most practical figure for sizing a boiler to meet a building’s load, because it shows how much heat you can rely on.

The gross rating, by contrast, counts heat produced before losses, which overstates what reaches the living spaces. An efficiency rating is a separate measure of how effectively the fuel energy is converted to heat, not the amount of heat delivered. And the term thermal rating isn’t the standard way boilers are described in most catalogs. For example, a boiler might produce 1,200,000 BTU/hr gross, but deliver only about 1,000,000 BTU/hr to the system in net rating due to losses.