over sized boiler

Ingvar

I just completed a heatloss calculation for my home using the SLANT-FIN CD and it comes up with a heat loss of just under 100,000 btu's.
My boiler (hot water loop) is putting out 165,000 btu's. It has twelve burners feeding off a manifold. If I remove four of the orifrices and plug them to bring the output down to about
110,000 btu's? Will I gain in efficiency?
In past winters I've noticed the boiler short cycling and am wondering if this would help.

Thanks in advance for any advice on this.

Jeff Krawic

firing rate

I believe you can remove some of the gas spuds on the manifold and you will definately reduce the firing rate input. However you really should have a qualified tech perform this kind of work. Playing with the "combustion side" of a system requires a little xtra knowledge and there is the risk of carbon monoxide production whenever you mess in this area. I highly recommend if you take the avenue of reducing the firing rate input to this boiler you have it tested with a quality combustion analyzer. Saving money does not bode well if the end result is a dangerous one. Consider the age of this boiler and consider having a good "Heat Loss Calculation" done on the building. These things will help you align your ideas. Good luck.

Steve Levine

Downsizing a boiler

can lead to lots of problems. First of all, they are AGA approved the way they are shipped. Not downfired. Secondly, if the correct burners are not removed, it could cause light off problems. Thirdly, that amount of downfiring could cause excessive condensation. And finallly for now, it could cause combustion problems, aggravated by a now oversized flue connection and draft hood.

Generally the amount of oversizing that you illustrate does not cause serious short cycling. Most boilers out there are that much, or even more oversized.

How short is the short cycling when the weather is very cold. What is the length of the on cycle? What is the length of the off cycle?

Be careful!

Steve Levine Slant/Fin

Steve Levine

The Slant/Fin Hydronic Explorer

program that he used will produce a good "Heat Loss Calculation". It is based uupon the I=B=R heat loss system.

Steve Levine Slant/Fin

Jeff Krawic

oooops....

Sorry about not answering your question on the efficiency. Most likely the "combustion efficiency" will show an improvement due to the lower stack temperature exiting the boiler. Combustion efficiency only uses 2 figures for the calculation. 1) CO2 (or O2) and 2) Net stack temperature. Losing 4 of the 12 burners should drop the net stack temp lower, however it may also reduce the CO2 reading due to excess air (if gravity or atmospheric burners) You would most likely do better with a properly sized boiler for the heat loss of the building. Newer boilers also have a reduced "stand-by loss" over the older ones.

John@Reliable

Downsizing gas boiler

I don't think I would, could open a can of worms.I would check aquastat settings and maybe add by-pass piping hard to say for sure without seeing the complete set-up you have.

Jeff Krawic

Oversized

Big thanks for responding Steve. I actually use the same heat loss CD myself. Have had NO problems with it so far. (and it also calculates the baseboard too!) I agree with everything you said in your answer above. This one is kind of touchy!!! Lets hope the info does not fall on deaf ears. Thanks for being here Steve.

Ingvar

No, it didn't fall on deaf ears

Thanks,I appreciate the quick responses.

I have been visiting this site for several years and have a lot of respect for the professionals on this site.

I appreciate the quick responses.
Here are some of the points which caused me to believe that down firing would be good idea:
The way I understood short cycling was that it would lead to condensation in the flue. Therefore longer burn times would alleviate this.
I would have removed just the two outer burners from each
side, leaving the center ones where the igniter and thermocouple are.
The short cycling occurs mostly when its warmer outside. From all your responses I gather that's not such a bad thing?

Let me try a different tack then. What about an outdoor reset control? Would that increase the efficiency? (the boiler is a Weil-McLain CGM-7-P1)

Thanks again, and don't worry, I'm not about do any thing with out researching it. (no garden hose gas lines)

Boilerpro

Out my way, the Weil Mclain supplier still sizes boiler by...

installed radiation for hot water. They say that's how Weil tells them to size them. There are lots and lots of brand new Weils 50% to 300% bigger than they need to be around here.


Boilerpro

Dana Zaichkin_2

What about a buffer tank?

If you're truly short-cycling, perhaps adding mass to your system would increase yor cycle times without having you (or a tech) mess with the explosive side of the equation.

Best Regards

DZ