Downfiring

nitwouttgrict2118451

Hi Keith,
Thanks for the reply. I did contact Burnham concerning reducing the boilers' output. The gentleman who wrote back stated it can be done (by a heating contractor) quite easily provided a combustion analysis is done afterward. He said the reduction usually only amounts to about 12 to 15%.

I was informed by others that there is a potential problem with un-even heating of the boiler sections if this is done. Is this true?

What are my other options, short of installing a smaller boiler?

Thanks, Roland

nitwouttgrict2118451

Downfiring

Hi All,
It has been said that a gas boiler can be downfired to reduce it's output. I have a Burnham PVG-4 (104k input, 90k output) that is about 3 times bigger than the Slant-Fin calculated heat loss.

This unit was installed by a "Professional" heating contractor who did no meaningfull heatloss calculation other than a back-o-the estimate approximation using the existing radiation. Either that or he just replaced the boiler with the same size as the one he removed.

I'm told that it's acceptable to reduce the boilers' output by 20%. How is this done? I'm not too comfortable with trying to do this myself so "Professional" help (god help me) will be required.
Thanks,Roland........

Keith_32

Downfiring can cause problems. Make sure to talk to Burnham before you do it, and get the guys name before you take tool to boiler. The chimney can be to cold if you downfire, the refractory patterns won't be the same. And if you're three times oversized a 20% reduction isn't going to help you much. There are other solutions that require more work but that will do the job for you.

Cosmo_3

You could....

take apart the sections, remove a few from the middle, put it back together, buy the appropriate sized burner, and cut the jacket to fit........

Or

Save a lot of time/money, as well as not mess with liabilities by buying a nice small gas-fired mod/con



Cosmo

nitwouttgrict2118451

De-Rating

Hi Cosmo,
I could borrow my brothers' SAWZ-ALL and have at it! Or I could stuff rags in some of the tubes. Seriously had I known this time last year, I'd have gone with a smaller boiler. The Mod-Con sounds tempting, but, I'll probably be pushing up daisies before I realize pay-back!

Roland........

Cosmo_3

Haha

Well, you never now about pay-back.

Try to run the numbers, you never know

Good Luck

Cosmo

siggy

wider differential

You might want to consider using an operating controller with a wide differential to fire the burner. This would be in series with other safety controllers, and the later would be set high enough to prevent interference with the operating controllers.

Wider differentials will "exercise" the inherent thermal mass in the boiler making it function similar to a buffer tank. The result should be longer but less frequent cycling.

I'm not sure what type of distribution system the boiler is connected to. If low temperature radiant - use a mixing device to smoothen out the supply temperature to the radiant circuits. I believe tekmar has a set point control that can go as wide as a 40ºF differential. An outdoor reset controller with automatically widening differential at lower load conditions would also help.

Again, make sure the operating controller with the wider differential is "backed up" by a high limit safety controller. We use manual reset high limit controllers on most of our designs, even when codes don't mandate it.