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Re: question about fire vs. water tube

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Posted by Boiler Guy on April 22, 2007 at 19:17:32:

In Reply to: question about fire vs. water tube posted by Tony on April 22, 2007 at 18:16:35:

Hello Tony,

In a lot of ways that is a non-question and neither answer is right or wrong. There are no set rules of how much heating surface one vs the other MUST have. I think what the question may have been geared towards was that firetubes by convention almost always have 5 square feet of heating surface per boiler horsepower, typically industrial watertube designs are around half of this.

Here's the real issue. The laws of thermodynamics do not care if the heat transfer takes place inside of a watertube or firetube. Total heating surface is only one component of the mathematics of heat transfer. A boiler with a lesser amount of heating surface could outperform a boiler with more heating surface (assuming identical operating parameters of course) if the boiler with lesser heating surface has a better overall coefficient of heat transfer. Heating surface is only one of many parameters. What about the furnace design and the release rates inside of the furnace? What about the pressure drop through the different types of boiler configurations and impact on fan HP? At the end of the day the answer is what do the different manufactures propose and guarentee and what is best for the given installation after doing a complete evaluation of the entire package.

It is meaningless to evaluate different boilers based solely on heating surface.

Boiler Guy

: I recently took an examination which asked if all other conditions were equal, would a fire tube or water tube boiler have more heating surface. I put water tube as the answer, but in the weeks since the test, I have found some evidence indicating that either answer could have been right. I am confused. Any thoughts?

: Thanks, Tony

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