Delta-T Charts

What is Delta-T?

When discussing delta-T the phrase can mean temperature rise or temperature drop. This term could also refer to boiler or system temperature changes. The temperature rise in the boiler has mostly to do with BTU input, thermal transfer and fluid flow. Boiler input and delta-t are set by manufacturers in high efficiency boilers and cast iron boilers are usually between a 20f and 40f rise.

System temperature drop is dependent on fluid flow rate, fluid temperature, heat emitter (radiation) construction , amount of installed radiation and air flow. System delta-T is usually between 15f and 40f dependent on heat emitter type and application. Through non fan style emitters as the flow decreases the output decreases. If the flow increases the emitter output increases. When hot water is passed through a coil and air passed across the coil the btu output is affected by fluid flow and air flow through and around the coil.

Heat emitters vary greatly in style and construction. To name a few they consist of copper tube/aluminum fin baseboard, steel pipe /steel fins, cast iron radiators and baseboard, radiant tubing, and hydro-air duct or cabinet coils.

Slantfin Radiation and Baseboard Output Chart

Burnham Cast Iron Baseboard and Baseboard Output Chart




Note: 400 LBS/HR or 2000 LBS/HR rating would equat to 1 gpm flow or 4 gpm flow respectively

20F Delta-T Chart

40f Delta-T Chart

The above charts show different Delta-T's at different water temperatures. Delta-T's are determined at a design system water temperature. You can measure delta-T increase or decrease with accurate thermometers. To calculate flow, you would need to use the Hydraulic Formula.

Disclaimer: The information found on this web site is for informational purposes only. Any and all preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or it's personnel accepts no responsibility for improper information or application, damage to property or bodily injury from applied information found on this web site.