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Posted by HeatPro on January 13, 2005 at 08:44:35:
In Reply to: Re: Dry Well Boilers posted by Eric on January 13, 2005 at 07:29:09:
A wet-base boiler requires construction to hold water in chambers around the fire box as well as in the passages above, so they tend to be heavier in construction and hold more water than a dry-base boiler. A wet-base boiler can have a target-wall on the back section and flame-retention boilers can often do without a chamber liner so the wet base can catch the radiant heat of the oil fire, so can be physically smaller than a dry-base which must have the lined base and more absorptive passages above. As a wer-base boiler holds water and has more metal to hold the water it is considered a large-mass boiler, so it takes a while to heat the mass and cool it down which affects the AFUE ratings.
A low-mass boiler often uses finned tubing to pass water by the fire, so carries less water. Low-mass boilers are more usually represented as gas boilers, as gas doesn't require radiant-heat absorption, so you will see them also as instantaneous heater. Some oil boiler manufacturers reduce the size of the steel and cast boilers through inventive design so are less mass,; but they don't get down to the lighter gas tubed boilers.
Large-mass boilers can be tolerant of water flows due to their slower heating and cooling as the extra weight absorbs the heat and the extra water allows local convection, so less technically-aware installers can 'get away' with indadequate system design, much like tank-type water heaters can be neglected and instantaneous water heaters with their small tubes cannot. Low-mass boiler installers must allow for adequate flow through the boiler to prevent sizzle and hammering. Many low-mass boiler manufacturers build bypass piping and internal pumps inside the boiler to provide that adequate flow.
It is a matter of taking care of the old-time truck or the brand new sports car, the determining factor of how long the machine will survive is a matter of which one requires diligent maintenance or not.
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