best indoor commercial wood boiler?

[Maynard]

Hi all,
Im new to this great forum. You guys have helped me greatly in the past through reading conversations.
I own a 28k sq. Ft. 3 story school Building in northern Illinois. I am converting it into an antique mall. It currently has a 750k btu Gas boiler to heat it. Im looking to heat it with a large indoor wood boiler. I've looked into and spoke with reps. From garn, econoburn, eko, tarm, royall. The most important factor for me is burn time. I will leave the building at 5:30p.m. and hope when I return in the morn. I still have hot coals at 7:30a.m. so I can simply throw some wood in and keep going. Im having a hard time finding a boiler that can handle more than a 3hr burn time. Is there something I can do to get a 12 hr. Burn time? I understand my BTUs won't be as high. What would you put in if you were in my shoes? All feed back is greatly appreciated.
Im thinking around 500k BTUs and letting my nat. Gas boiler pick up the rest.

 

[maple1]

Perhaps you should shift your thinking just a bit, and not focus just on burn times. Batch burning into storage should be more efficient - if you have space for lots of storage. That's a pretty big space your heating - do some searching for posts by jebatty, or search for 'deep portage'. He's got lots of time on 3 different boilers in that kind of situation. A pellet boiler might be another possibility?

Edit: I would put a big garn at the top of my candidate list.

 

[flyingcow]

Have you looked at a comm pellet boiler? Up here the cost per btu is about the same as cord wood.

Heaterman might have some input in something as big as this. He's done some pretty serious installs.

 

[Maynard]

The natural gas boiler would act as my pick up the slag/auxiliary heat. The reason im looking at going with a wood boiler with around 500k btus is simply because it's what my budget allows for. The biggest garn 700k btus is $40k (too much$) The next size down is $15k- something like 480k BTUs( just right$).
Basically im wanting to undersize my wood boiler so it fits my budget, get a long burn time and let the natural gas boiler pick up the rest and take the savings I get... Any way to do that? What would you install? Thanks again and look forward to feed back!

 

[maple1]

Again, don't think burn time. Rather time between burns. The onboard storage of the garn will keep putting out heat long after the fire is out. Extending burn times comes at the expense of extended periods of smoldering.

 

[Maynard]

just got your feedback thanks much! I looked into a bio burner that would do my building it was over 40k. i then looked into more different pellet burners and I felt like pellets were competing too closely to natural gas. I guess im looking for big savings like 80% like I think I'll get with wood over 30% like I THINK id get with pellets. At least what I prices out for pellets around this area.
Idk. Im thinking about going cheap and going with the biggest royall and just seeing what it will do. Any red flags? I know it's not a gasifier. Maybe I'll lose in cords?

 

[Maynard]

Ahh.. Thanks maple1. Great point. I can see that heat storage as a good thing now.

 

[Maynard]

maple1. Will I have to make a fire every morning then? Is it a very big deal? Will hot coals be waiting for me to throw more wood on and get going?
The reason im thinking royall is because im assuming I can fit more wood in a boiler that is not a gasifier thus having a longer burn time.?

 

[BoilerMan]

What is your cost of wood and what is your cost of NG? NG is so cheap now I'd look into this more deeply.

Also, how old is this school building? Is it heated with steam or hot water, most buildings around here of that size built before 1970 are heated with steam. Steam is a whole different animal, and will rule out most wood boilers, and will rule out any storage. You can't store steam.

TS

 

[hobbyheater]

maple1. Will I have to make a fire every morning then? Is it a very big deal? Will hot coals be waiting for me to throw more wood on and get going?
The reason im thinking royall is because im assuming I can fit more wood in a boiler that is not a gasifier thus having a longer burn time.?

 

[JP11]

If you have NG…. I can't imagine you're going to save anywhere near 80%.

Even if you have "free" wood. Heating that 3 story beast will get to be a second job. It won't take long before your wood hobby gets old. If you calculate in your labor, that free wood isn't going to compare as good with NG as you think.

How's the building insulated? How are the windows? I would think that money spent there will have a better impact.

JP

 

[jebatty]

I agree with the others that focusing on burn times in not the right question to ask. I would start by determining your usage of natural gas to get an idea of how many btu's your need because you then can convert that to the approximate amount of seasoned firewood you will need. Next I would consider how hot your hot water needs to be to meet demand. Can your building be adequately heated by 130F water (or lower) or do you need 160F water (or hotter)? If you need 160F water (or hotter), you likely will need to burn nearly continuously unless you have boiler btuh capacity much in excess of demand and plenty of storage to provide heat between burn periods. The lower your need for hot water the greater the flexibility you will have with boiler sizing and with storage to extend heating times between burn periods.

An important consideration for you, because you will have a commercial space, may be whether or not you need ASME certified boilers and hot water storage tanks. These may be code-required or required by your insurance carrier. Your insurance carrier also may not be pleased by wood boiler and hot water storage tanks in your commercial building.

Now, looking a burn times, your question, with an assumption: assume your heat demand will be 350,000 btuh and your choice is a high efficiency wood boiler (gasification). 350,000 btuh means about 70 lbs of seasoned (20% MC) wood per hour at 85% boiler efficiency. If this demand extends over a 24 hour period, that is about 2/3 cord per day of oak. Adjust the assumptions as you feel appropriate. With my assumptions, to get a 5 hour burn time, you would need a boiler that could take a wood load of 350 lbs. I'm not aware of a gasification boiler with this capacity.

Or, if you are looking at a large btuh capacity (greater than 350,000 btuh) boiler with storage to extend times between wood loading, and assume you need 130F water and assume you can pre-heat storage to 185F, then you will need about 765 gallons of 185F storage water for each hour that your heat demand will be served by water storage. For an eight hour period that is about 6000 gallons of hot water storage: a very large tank(s) and expensive.

In some respects Deep Portage was in a similar situation to yours but in a much colder climate (-25F right now as I write this): LP boilers mostly supplying water to air heat exchangers, 56,000 square feet in a two level, older building, and huge heating costs. It also is located in an area of plentiful wood supply. It's solution was a separate "Energy 3" building just for the wood boilers and hot water storage, staging area for about a day's supply of wood, and an equipment/shop area. The separate building was dictated by lack of other available space and insurance requirements. DP also had a large outdoor area that holds 100+ cords of c/s/s seasoned firewood in wood sheds, all supplied by local firewood dealers. DP kept in place its LP boilers but rarely, if at all, has had to put them in service since the wood boilers were installed. Yet they were left in place for backup. And DP has 24-hour staff to fuel the boilers as needed during the night.

The choice was a Garn WHS3200 and a Wood Gun E500, and subsequently 4000 gallons of hot water storage was added to primarily serve the WG. As a result of weighed wood burns over extended periods the sustained output of the Garn was measured at 500,000 btuh and the WG at something over 500,000 btuh. Search for my posts for Deep Portage and you will find extensive information on these boilers. DP is satisfied with its choice and has saved a very large sum of money by switching to wood, plus its wood usage is keeping jobs local and money local for support of local families.

 

[PassionForFire&Water]

First to do: figure out the school buildings NG usage for the last 3 years.
Then, based on Heating Degree Days for your location figure out your max heating load.
I would strongly advise to hire a professional to assist you in this. This will be money well spent.

In my opinion cord wood will not work.
it's not gone be a pleasant hobby for very long. Just to much work.
If you need to hire somebody to load the wood boiler then you need to factor this into the price.

Did you look into wood chip boilers: Heizomat, Fröling, BioBurner, ... ?
Wood chips are around the some cost as cord wood, ie if available in your area

 

[ihookem]

I think you need to insulate the heck out of it before you do anything. No matter what the cost of insulation , it is cheaper than any form of btu's and you inulate once. Hope it's well insulated, but most likely it's not because americans have this mental block when it comes to super insulated buildings. Then find out what the heat load is. I imagine a garn is your best option because of the heat load.