one boiler or two

mark_87

thanks everyone for your replies. Yes tanks are definately indoors, dont need the hassle of freeze ups in the winters. Have seen too many problems with the direct vent units...had to do significant repairs to a house up here that froze up after a unit failed, the boiler worked fine but without that vent, well........ The inn is divided into 12 zones controlled by 2 taco zvc 406 controllers, one zone is for DHW, one is futured for radiant in an area of the house that is currently being rehabed, the rest for baseboard heating in guest rooms, etc as well as 2 small modines in crawlspaces. It does sound like 2 small boilers would be of savings in the long run.

mark_87

one boiler or two

currently have a Vailaint boiler 240000BTU which also heat my DHW with a 50 gal indirect tank. house is 200 yo inn in upstate NH. Boiler does a decent job and heat loss calcs seem to indicate that boiler is correct size. However this thing is a fuel hog though tuned to within an inch of its life. Looking at changing to either a Buderus G215 of appropriae btu output or two Buderus G115 totaling the needed btu output controlled by a taco 702 controller to alternate boilers, etc. any thoughts as to fuel savings if two smaller boilers are used? I am being told about a one third reduction in fuel usage, but...

kevin coppinger_4

for what its....

worth...I would do the one 215 and do a Logamatic control w/ the room sensor(2105)...especialy if you have CI radiation....kpc

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Brad White

Some thoughts

When speaking of savings, it all gets down to actual heat loss, the ability to modulate or adapt firing rate to that load and the number of hours at reduced heating demand. (It is only at design cold temperatures between 1% and 2.5% of the time; the rest of the time it is much higher.)

Let's say your 240 MBH is the input and that your actual load is in the 190-200 MBH range. If you had natural gas or even propane and can find a single ModCon to handle that and modulate down to 25% that could be a good fit.

Seems you have only oil so that limits your options to what is available in two-stage burners. Not sure if two-stage is available in those relatively small sizes. I suspect not.

Thus, I would strongly recommend two paired staged boilers at 50% of load capacity. You are covered on a peak day but most of the year's heating hours, one should do the trick. You also have a two-engine airplane now and what is that peace of mind worth?

The proper controls (Tekmar as after market; not sure what Buderus offers directly, or the Taco) can pair them, lead-lag them for even wear, stage them appropriately and prioritize domestic hot water.

With one large boiler, you will cycle on-off much of the year, while with two boilers, one of them will handle the reduced load more efficiently, running steady-state for longer. Overall your plant will last longer because each boiler sees fewer hours of run-time too.

The other half of the equation is the heating distribution system- is it piped primary-secondary to allow deep reset? (Outdoor reset is proportionally changing the hot water supply temperature indexed to the outside temperature).

Think of it all as a system. Do that and a 30% savings would not surprise me compared to a single-temperature one-stage boiler.

My $0.02

Brad

John_82

2 G213/3 boilers with R2107 reset control and the FM242 staging card. This gives you outdoor reset and fires the boilers as needed. 215 boilers are "thermostream" boilers, so you can get away from primary/2ndary piping. That is something to think about if you have cast iron radiation... No need to protect the boilers from low temperature return water. The boilers would get piped reverse return w/ a small thermal bypass after the supply sensor. Nice & easy!! This is how I'd lean if using 2 boilers.

colbydoglvr_3

two boilers

I would use two G 115 boilers and a Tekmar 262 two stage boiler control. This control will also run an Inderect hot water heater if you choose. the g 215 is a nice boiler but is louder than North Conway on a summer weakend. really kinda sounds like a locomotive with a jet engine. depending on your chimney and chimney cap setup you could end up hearing the boiler thruout your home. Buderus does make a muffler setup for the g 215, lmao. If you have a BLUESTONE cap on your chimney even the folks down the road at your local graveyard might just wake up... two boilers ARE better than one. buderus 115 's are very nice quiet little boilers. STAY AWAY FROM DIRECT VENT BOILERS AND PUT YOUR OIL TANKS IN A HEATED PART OF YOUR BASEMENT. TRUST ME.

Maine Doug_52

In my

commercial/residential building, the steamer was replaced with twin boilers. Bought the software to do my own calcs since the companies I contacted