What Size Boiler

[Briquetmaker]

New here, could really use some help. I've read a lot of great information. I'm not sure how to zero in on the size of the boiler needed for my space.
I have a 6700 SF wood shop with 12 FT ceilings. We are in the process of putting in an oil fired boiler which is ultimatly going to be the backup unit. The rating the salesman came up with was for a 286K unit which is sitting in the boiler room waiting for me to make a decision on a wood boiler (winter's coming). There are wall hung two tier H-6 steel fin tube installed. There is about 80 FT of it which puts out about 1800 BTU's per foot. There is another 75FT of regular aluminum slant fin. I like the Tarm 60 but not sure if it will be large enough without storage and if I add storage will I be way off. Comfortable temps in the shop are usually around 65* so I'm not sure how to calculate the actual demand. The one good thing is I make all the fuel I need with a briquetting press that was installed in March.

Any suggestions would be much appreciated.

 

[Piker]

New here, could really use some help. I've read a lot of great information. I'm not sure how to zero in on the size of the boiler needed for my space.
I have a 6700 SF wood shop with 12 FT ceilings. We are in the process of putting in an oil fired boiler which is ultimatly going to be the backup unit. The rating the salesman came up with was for a 286K unit which is sitting in the boiler room waiting for me to make a decision on a wood boiler (winter's coming). There are wall hung two tier H-6 steel fin tube installed. There is about 80 FT of it which puts out about 1800 BTU's per foot. There is another 75FT of regular aluminum slant fin. I like the Tarm 60 but not sure if it will be large enough without storage and if I add storage will I be way off. Comfortable temps in the shop are usually around 65* so I'm not sure how to calculate the actual demand. The one good thing is I make all the fuel I need with a briquetting press that was installed in March.

Any suggestions would be much appreciated.

looks like the total emitter output is only about 190,000 btu's/hr. Wondering why such a big unit was recommended... but perhaps I am missing something? Do the current emitters keep up with demand on cold days or are you planning on adding more?

Storage probably won't work great with the type of emitters you are using since they are high temp. Perhaps right now it's best to install a gasser without storage and gage your fuel loads according to the temperature outside... keeping the smallest, but hottest fire possible at all times. A small buffer tank might be in order to smooth out the cycles.

cheers

 

[Briquetmaker]

I can see that experience plays a big part in getting right. There was an OLD monster oil boiler installed and was running with a 2.5 or 3.0 nozzle so I was spending quite a bit on oil. The large emitters use 1-1/4" black pipe and 4-1/4" fins and there is a double row. Is that too much water to dump back into the boiler?

 

[Piker]

I can see that experience plays a big part in getting right. There was an OLD monster oil boiler installed and was running with a 2.5 or 3.0 nozzle so I was spending quite a bit on oil. The large emitters use 1-1/4" black pipe and 4-1/4" fins and there is a double row. Is that too much water to dump back into the boiler?

Your gasser will be installed with return protection in the form of a loading unit or a thermostatic mixing valve... it will temper the return water regardless of the volume. There will not be an issue with too much water being dumped back into the boiler.

cheers

 

[Briquetmaker]

I'm going to get the calculations the oil boiler supplier used for his sizing. The shop did heat up quickly when needed. Do you think using a 200K boiler is right on the edge of not being large enough?

 

[btuser]

You pick the closest sized boiler after doing an accurate heat loss calculation. I've got a 4300sqft house and over 1000 sqft of it has 12f cathedral ceilings. My heat loss came in @ 75,000-80,000 btu/hr. I installed a 100k btu/hr, and removed a 164k boiler that was installed before a 1200sqft addition. It is very very common that boilers are over-sized by 50-100%. My plumber-in-law suggested a 194k boiler, and said the one I install will never, ever keep up. I asked him if he's ever installed a boiler that was undersized and he said "no way, I always make sure its big enough". Enough said. I guess it was common at the turn of the century to size boilers large enough to heat the house on the coldest day of the year with all the windows and doors open. Something about a fresh air curing the flue pandemic.


That 288k boiler was more than likely sized for the design temp, which is the coldest expected day of the year. You won't need that but for maybe 10 days a year.

 

[Piker]

I'm going to get the calculations the oil boiler supplier used for his sizing. The shop did heat up quickly when needed. Do you think using a 200K boiler is right on the edge of not being large enough?

It's hard to say without knowing what the actual heatloss of the structure is. Just because you have 190,000 btu/hr worth of radiation does not mean that you have 190,000 btu's of heat loss.

if 190,000 btu's worth of radiation is adequate on even the coldest days, then I would suggest that a 200,000 btu gasser should be able to handle the load nicely. The biggest variable that you will face is burn time. Taxed at maximum output, gassers tend to run through a load of wood in 4 or 5 hours. If you're around to keep feeding the boiler, this is actually advantageous from an efficiency and emissions perspective.

When installing gassers without storage, I try to encourage people to size as small as possible... or even undersize. If you can manage the burn times, and if you are willing to burn a little fossil fuels during just the coldest parts of the year... the smaller boilers run very clean.

cheers

 

[btuser]

Yeah, what he said.

 

[Briquetmaker]

You guys have been very helpful and I appreciate you taking the time to educate a beginner. It has been a year and a half since I thought about going this route but I needed to start with the briquet maker.Once I get the heat loss from the oil guys I should be good. Is there any downside to putting in a boiler thats just big enough without storage and adding storage later? Would the boiler struggle with 1000 gal storage? I guess the oil would pick up the slack on the very cold days?

 

[btuser]

If you're going to near-size the wood boiler it may cut back on the amount of storage that would be practical to try and heat. The big advantage to storage (I'm guessing here) is the reduced number of firings, so you'd have to oversize in order to be able to charge your storage. This of course is only going to be an issue on the coldest days.

 

[Piker]

You guys have been very helpful and I appreciate you taking the time to educate a beginner. It has been a year and a half since I thought about going this route but I needed to start with the briquet maker.Once I get the heat loss from the oil guys I should be good. Is there any downside to putting in a boiler thats just big enough without storage and adding storage later? Would the boiler struggle with 1000 gal storage? I guess the oil would pick up the slack on the very cold days?

Remember that with storage, you need to have enough boiler output to cover the heat load plus some additional output to place into the tanks. If you're boiler's output is very close to the load, storage may not be an option during the coldest parts of the winter. This doesn't mean that storage can't be used when the weather is more moderate, however... and could lengthen your burning season far into the shoulder seasons without worry of disturbing the neighbors with smoke. A couple of well placed ball valves, and you can bypass the storage when needed. If I remember correctly from our phone conversation, you will be available for firing throughout a 12 hour work day... so if you install 1000 gallons of storage, technically you could take as long as 16 hours of full bore firing to get the storage up to temp if needed. Since you are available for frequent reloading, this might not be a bad scenario even on the coldest days of the year... but it depends on actual heat load and what the usable temperature differential is of your emitters.

cheers