How can I determine the effiency rating of an old boiler

Old 10-11-07, 04:43 PM
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How can I determine the effiency rating of an old boiler

We have hot water heat and are considering replacing our 1981 Repco boiler (model #1A150C) I am looking at new boilers that are 85% efficient and 95% efficient. How much of an improvement in efficiency will I get? how efficient is the old boiler? What is the average lifespan of a boiler?
Old 10-11-07, 05:52 PM
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The kind of efficiency you are looking for is not measured with a test instrument. That's why the government can't put a number on it either. It is very important for us to know if you use your boiler for domestic hot water in addition to heat. That is where AFUE numbers are misleading. You also did not tell us what the fuel is. Natural gas, LP gas, oil? You will most likely get a large and varied response to your question after the blanks are filled in.

Old 10-11-07, 07:18 PM
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thanks for the prompt response...sorry I left out the important details. I am new at this. The boiler is used for heating only and is fueled by natural gas.
Old 10-12-07, 03:04 PM
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With your existing boiler being a 1981, I am presuming it has a pilot which stays lit all the time. If this is true, you are probably looking a somewhere in the 60% efficiency range.

If you are looking for efficiency, you can't beat the wall hung boilers. They won't last as long as a real boiler but they are efficient.
Old 10-12-07, 08:45 PM
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Between a conventional atmospheric boiler at 80-85% and a modulating condensing boiler at 90-95% there is probably a savings of at least 30% in fuel. The saving will be greatest when the loads are lowest.

Unless the boiler load can equally match the rate of loss in your house, you will have a loss of comfort and efficiency or equipment cycle life. A typical atmospheric boiler makes heat at a much faster rate than the building will leak it.

So the boiler will have to be pulse fired to match the load. The controls determine the length of the pulse. Short pulses and the the comfort will be better and the efficiency as well, but the equipment will lose life cycles and won't heat enough to keep corrosion away. If it heats long enough to warm up the flue like it should then you add way too much heat and have temperature swings. The body will have a minimum comfortable temperatures and that will be the bottom of the comfort range so the average moves up and so does your heat loss. In addition all that heat in the flue forms a heat sink. As it gets colder and colder, it gets closer to steady state efficiency but still loses more heat up the flue (that 10% difference). Most conventional boilers seldom even get to run for 1 hour steady.

A modulating condensing boiler on the other hand does not need to worry about condensing. It can pulse fire low comfortable temps and not worry about condensation, in fact these are most efficinct when adding heat to cold return water. It sucks more heat from the heat exchanger that way.

Furthermore, through modulation, steady state non stop firing can be achieved at colder temps to help with economy there. No modulating condensing boiler should ever have a minimum firing that is higher than the heat loss so they get an advantage there over conventional atmospherics.

There are a lot more mild heating days in a year than frigid design days. 30%... and I'm serious.

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