Does a Drop Header Give Dryer Steam?

Steam Header

• Steam rising from your boiler is a mix of hot water droplets and hot water vapor, which is a gas. The mix of steam vapor and water droplets travels up a vertical pipe known as a boiler riser. It enters one end of a horizontal pipe section known as a header, where the hot water droplets condense into liquid for return to the boiler. The drier steam rises into the system-distribution riser at the other end of the header that goes to the building’s radiators.

Wet and Dry Steam

• “Dry” steam is hot water vapor with virtually no water droplets by volume. Steam with a substantial percentage of water droplets is called “wet” steam. You don’t want wet steam, because it moves slower and travels a shorter distance than dry steam before condensing into liquid water. If steam is too wet, the radiators at the far end of your steam-heating system won’t get enough steam to be really hot. Your boiler will run longer in an attempt to produce enough steam to satisfy the far-end thermostat’s demand for heat.

Dropped Header

• A dropped header produces drier steam than a traditional header mounted above the boiler. A dropped header is piped with elbows to be lower than the top of the riser pipe from the boiler, so that steam from the riser enters the header from the top rather than from below or to the side. By entering the header from the top, the steam coming from the boiler doesn’t roil the condensed water already in the header, so it doesn’t pick up additional water droplets.

Turns Help

• The turns leading down to the dropped header also slow the velocity of the steam, aiding the separation of dry steam from the water droplets. The dropped header also is larger than the boiler riser pipe, further slowing down the steam, so it lets go of more water before rising up to the radiators. The condensed water drains out of the dropped header back into the boiler. By eliminating liquid water droplets from the steam flow, a dropped header also reduces hammering noises as the steam rises.