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Re: Boiler Oversized

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Posted by Kris on March 08, 2005 at 18:22:16:

In Reply to: Re: Boiler Oversized posted by HeatPro on March 08, 2005 at 10:30:22:

Is that why the boiler doesn't short cycle and will run for 15 minutes and the temp maxs out at around 115-120? My radiant flooring contractor wants to have 125 degree water. Is this possible if the rest of the system never goes above 115-120.


: Your conclusion is incorrect because it is based on a misunderstanding of how a hot water system works. A boiler will remain at a low temperature because there is TOO MUCH RADIATION for the boiler. If the radiation gives off all the heat than the boiler can make at 120F, as yours shows evidence of doing, then the water temperature can not rise higher than the temperature required to output all the heat. That is how a boiler is matched to radiation, so there is enough radiation to give off heat of the boiler at the design temparature.

: How did that other person determine the efficiency of the boiler? Did he use a combustion test kit or test it in a laboratory? Otherwise, if the boiler is running as designed, it is over 76% efficiency and wouldn't be less. Running at low temperature increases the efficiency of a boiler by making it absorb more heat.

: The important point though, is that your boiler shouldn't be running at that low a temperature, as it is condensing water either in the passages and/or the chimney venting. You would be better off with a Weil Ultra, as you would get 94% or so efficiency and it is designed to run at the low temperature you have, so you could leave the radiation as is and add more for a radiant floor that runs well at that temperature.

: The other choice is to change the near-boiler piping to a boiler subloop and keep the boiler operating temperature over 150F while the burner is on.

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