Fuzzy Math...add-on boiler sizing...does this work?

[WRPage]

I’m trying to pay heed to the “don’t get a boiler that’s oversized advice”…I would appreciate it if some of the experts could tell me if the fuzzy math below works for sizing an add-on wood/coal boiler (yes…I am trying to avoid the heat loss calculator for now…figured I’d try this method first.)

Also…I’m using 55% efficiency for the boiler. I’m looking at buying a New Yorker and don’t yet know what the actual efficiency will be. I am aware there are more efficient units out there but price and availability are factors. Does 55% sound reasonable?...hopefully it's low, not high.

My existing oil fired boiler = 102k BTU/HR @ 87% eff. = 88,740 NET IBR BTU/HR

This boiler is what’s been keeping us warm…we use about 8-900 gallons per year. This includes domestic hot water.

NY’er Boiler Sizes:

WC-90 = 90k BTU/HR @ 55%? eff. = 49,500 NET IBR BTU/HR
WC-130 = 130k BTU/HR @ 55%? eff. = 71,500 NET IBR BTU/HR

If my fuzzy math works at all, it looks like the WC-130 would not be oversized…am I missing something…am I missing a lot, or is my math close enough to work?

I plan on adding storage down the road but it’s not in the wallet right now.

Thanks a lot!

 

[steam man]

Without a heat loss you have some wild cards here. Especially since you may add storage later. My gut feeling says to go with the smaller unit and fire it hard when you need it from looking at your heat requirements. My dad had the WC-120 and without a load it smoldered and blew the the relief valve, not to mention creosote and chimney fires. I think a gassifier would tend to cycle "cleaner". A non-gassifier should never be cycled from my experience. The units efficiency would probably be higher running hot and hard. Even at the heat output at 55% for the WC-90, your house doesn't sound like it is anywhere near that heat demand. Storage negates a lot of this but even the smaller unit can heat a tank over time.

Mike

 

[Bob Rohr]

I agree with S-man. The load needs to be determined to size ANYTHING. Does the current boiler cycle off on the coldest day of the year? If so it is probably oversized.

In a perfect case the boiler, any boiler would run non stop on a design (coldest) day. So it would produce heat at the exact rate the building loses heat.

Fairly hard to hit that exactly. Typically boilers were always oversized a bit. Fuel was cheap, why not.

In your case, with proper piping, go with the smaller wood boiler and leave the ability for the oil boiler to contribuite to the load, should the wood fired one fall short, or you leave town, get bored with wood, etc.

This is why I try to encourage piping options that allow any or all boilers and loads to live in harmony

There is no reason not to pipe for multiple options like, addition of storage, addition of solar input, home or room addition, etc. The sky is really the limit with hydronic, unlike replacing large duct work in a forced air system.

The system piping I have shown in the other post would allow these options.

When the wood boiler is fired the oil boiler sits at room temperature, no flow through it, no burner firing, no idle temperature, nothing.

If the wood is off, same thing, no flow, no temperature.

both could fire until the loop reached a pre determined temperature, the oil fired drops out, flow through it stops, and it settles to room temperature again.

Other options include priority. typically DHW would be a priority zone. you should never run short of DHW regardless of which boiler is fired. With children, dhw can be a large load, cover it with your wood fired boiler when at all possible. Better yet solar All other heating stops until the DHW tank gets hot. Again one or both boilers could contribute to that load. In summer months, the oil fired boiler alone would generate DHW without flow through the wood boiler OR the storage tank. Or better yet solar DHW in the summer.

hr

 

[WRPage]

Without a heat loss you have some wild cards here. Especially since you may add storage later. My gut feeling says to go with the smaller unit and fire it hard when you need it from looking at your heat requirements. My dad had the WC-120 and without a load it smoldered and blew the the relief valve, not to mention creosote and chimney fires. I think a gassifier would tend to cycle "cleaner". A non-gassifier should never be cycled from my experience. The units efficiency would probably be higher running hot and hard. Even at the heat output at 55% for the WC-90, your house doesn't sound like it is anywhere near that heat demand. Storage negates a lot of this but even the smaller unit can heat a tank over time.

Mike

Steam Man...Thanks a lot for you feedback...when you say, "A non-gassifier should never be cycled from my experience", do you mean the boiler should not be set up so the blower cycles on and off when a zone calls for heat? If the boiler burns wide open whenever it's lit, wouldn't this be a waste of fuel without storage? Would all the heat not sent to a zone be sent to the dump zone until a zone calls? If the best plan is to run it wide open, is this desirable strictly to prevent creosote?

Thanks again - Bill

 

[WRPage]

I agree with S-man. The load needs to be determined to size ANYTHING. Does the current boiler cycle off on the coldest day of the year? If so it is probably oversized.

In a perfect case the boiler, any boiler would run non stop on a design (coldest) day. So it would produce heat at the exact rate the building loses heat.

Fairly hard to hit that exactly. Typically boilers were always oversized a bit. Fuel was cheap, why not.

In your case, with proper piping, go with the smaller wood boiler and leave the ability for the oil boiler to contribuite to the load, should the wood fired one fall short, or you leave town, get bored with wood, etc.

This is why I try to encourage piping options that allow any or all boilers and loads to live in harmony

There is no reason not to pipe for multiple options like, addition of storage, addition of solar input, home or room addition, etc. The sky is really the limit with hydronic, unlike replacing large duct work in a forced air system.

The system piping I have shown in the other post would allow these options.

When the wood boiler is fired the oil boiler sits at room temperature, no flow through it, no burner firing, no idle temperature, nothing.

If the wood is off, same thing, no flow, no temperature.

both could fire until the loop reached a pre determined temperature, the oil fired drops out, flow through it stops, and it settles to room temperature again.

Other options include priority. typically DHW would be a priority zone. you should never run short of DHW regardless of which boiler is fired. With children, dhw can be a large load, cover it with your wood fired boiler when at all possible. Better yet solar All other heating stops until the DHW tank gets hot. Again one or both boilers could contribute to that load. In summer months, the oil fired boiler alone would generate DHW without flow through the wood boiler OR the storage tank. Or better yet solar DHW in the summer.

hr

Master of Sparks...Yes, the current boiler cycles on and off. It took me a few reads to understand the logic of "a boiler running no-stop"... but when I thought about it with a woodboiler in mind, it made perfect to match my existing boiler's capacity doesn't make any sense as it would certainly be too much heat without cycling often or dumping heat.

Thanks for your piping suggestions...as far as hot water goes...I heard elsewhere to run the water heated by the wood boiler through the oil boiler so I can still use that coil for my DHW. The methods you suggest won't allow me to do that if I'm understanding it. Although minor, wouldn't the additional water volume in my oil boiler be beneficial? What is the benefit of leaving the oil boiler idle?

I'm just trying to figure this out so I can help my plumber come up with the best design possible. Thanks Master!

 

[steam man]

Without a heat loss you have some wild cards here. Especially since you may add storage later. My gut feeling says to go with the smaller unit and fire it hard when you need it from looking at your heat requirements. My dad had the WC-120 and without a load it smoldered and blew the the relief valve, not to mention creosote and chimney fires. I think a gassifier would tend to cycle "cleaner". A non-gassifier should never be cycled from my experience. The units efficiency would probably be higher running hot and hard. Even at the heat output at 55% for the WC-90, your house doesn't sound like it is anywhere near that heat demand. Storage negates a lot of this but even the smaller unit can heat a tank over time.

Mike

Steam Man...Thanks a lot for you feedback...when you say, "A non-gassifier should never be cycled from my experience", do you mean the boiler should not be set up so the blower cycles on and off when a zone calls for heat? If the boiler burns wide open whenever it's lit, wouldn't this be a waste of fuel without storage? Would all the heat not sent to a zone be sent to the dump zone until a zone calls? If the best plan is to run it wide open, is this desirable strictly to prevent creosote?

Thanks again - Bill

Let me explain. I have watched a New Yorker run for some years. Nice boiler but it doesn't like a no-load situation. It probably runs the fan until it hits 180 then on again at 160. My dad's boiler was oversized and spent plenty of time smoldering, making creoste, and blowing the relief valve. And the chimney fires. In this traditional boiler a lot of unburned gases just keeps going up the stack. I think a gassifier can go through a shutdown cycle better by design. Making sure you are not oversized so it can run flat out and hopefully planning for storage is the way to go to minimize cycling.

Mike

 

[John Giulietti]

Does anyone have experience using either the New Yorker WC-90 or WC-130 burning "nut coal" rather than wood? Regards, /s/JLG

 

[Wood Pirate]

How did you make out with your sizing calcs.
I have a W-90 on order which should be coming in any week now so I will be picking brains on the same subject shortly. I have been concerned about keeping it running at a good pace. My current boiler has a zone which runs to a Bock 50 gallon indirect hot water heater. I am hoping that this is a good thing.

Paul