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To Boiler or not to boiler

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Eric Miller, Mar 10, 2008.

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  1. Eric Miller

    Eric Miller New Member

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    Hello all. I found this forum a couple of weeks ago and reading the various posts here sure has got me interested in a Gasification Boiler. I downloaded the Slant/Fin (http://www.slantfin.com/heat-loss-software-order.html) Heat Loss Software and that tells me my peak heating load is 65,000 BTU for my 4,000 square foot three level house here in Maryland based on 0 degree outside temperature and 70 degree inside. I assume that means a smaller boiler would be appropriate for me, like a Tarm 30 or EKO 25 or 40. I currently have two Heat Pumps, one supplying the Basement and 1st floor and one supplying the 2nd floor. I am comparing the costs of the following two scenarios:

    Option A - Installing a Wood boiler system tied into my two forced air heat pump systems and also plumed to provide DHW. I would also use it to feed a radiant floor heating loop I want to install in about 140 square feet of bathroom and closet that is positioned above my garage.

    Option B - Install a second wood stove in my basement with a new (start from scratch) chimney and also install a Solar Hot Water Heater to provide DHW. This system would also require that I install an air duct from my basement to the second floor to connect to the cold air return on the second floor heat pump in an attempt to mechanically redistribute warm basement air to the second floor. For safety, the stove would use an outside air kit and the return air duct would be 10 feet away from the stove and equipped with a smoke/carbon dioxide alarm and an automatic fire damper.

    A quick back-of-the-napkin calculation shows the costs of the boiler system would be about 10% more but I'm sure it would also result in a much more even and comfortable heat distribution throughout the house. However, the Boiler would also require me to construct a small out-building to house the boiler and water storage tank. That could drive the costs up considerably but the building could serve a dual purpose boiler room / shed role so I am not factoring that cost too heavily at this point. The outbuilding would also sit pretty close to the house, about 25 feet, so I'm assuming that it wouldn’t result in too much of an efficiency penalty.

    How does one go about designing a wood boiler system? I inquired with a couple of manufactures for local installers but so far no luck. In any case, I guess I'd also like to do as much of the work I can myself but I would plan on hiring a local HVAC contractor for assistance in installing the water/air heat exchangers in my air ducts. I'm comfortable doing plumbing work but it would seem a system of this type has to be designed properly to work well if at all.

    I would only want to feed the boiler once a day during the heating season, maybe twice a day if it's really cold or we are using more heat then usual. Is that a reasonable expectation? Assuming you are using properly seasoned wood, how easy is it to start a cold boiler? Can I just load in a few cubic feet of wood, some kindling and paper, light a match and walk away? Do they need any attention during the burn cycle? What kind of maintenance does a boiler require?

    Thanks for your help.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    Option A sounds like a winner to me.

    Designing a hydronic heating system is no different whether you're using a fossil fuel boiler or a wood-fired gasifier, really. There are a few differences at the boiler itself, but on the house side of things, it's all just hot water getting moved around to the right place. There are plenty of system diagrams here in various threads. Any competent heating professional could do it for you, even if they didn't touch the boiler itself. Or, if you're a halfway decent DIY type, you can probably figure it out with a little help. Many of us did that, and we're still learning.

    The outside shed/boiler room sounds good. Make it as big as you like. So long as it's not an attached garage, it should be OK.

    With hot water storage, you could probably get away with firing the boiler up once every two or three days in your climate, most of the winter. I'd say once a day, tops, and that might be overkill in MD. Starting a fire in a gasifier like an EKO is about as easy as starting a fire in a woodstove, and maybe easier since you've got a draft blower to do most of the work. Basically, you get a nice little fire going, fill it with wood, close the bypass damper and walk away. No smoke after the first 15 or 20 minutes--sometimes a lot quicker.

    About the only routine maintenance with a boilers is emptying the ash pit out periodically. Probably about once a week at most in your case.

    I'd say it's easier than a wood stove, on balance.
  3. Eric Miller

    Eric Miller New Member

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    Thanks Eric, I will search around for schematics and see what I can come up with. Is there a formula that will tell me how many btu I can extract from a given amount of water at a given temperature? Also, what efficieny loss should I use to calculate for water to air heat exchangers?
  4. heaterman

    heaterman Minister of Fire

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    Formula: Temperature drop x GPM x 8.33 x 60 = BTU/hour

    Heat transfer capability is not so much an efficiency question as it is simply a function of area of the heat exchanger. A water to air HX will simply do what it does based on air flow CFM on the outside and GPM/temp on the inside.
  5. Eric Miller

    Eric Miller New Member

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    Thank you for the formula, unfortunately I didn't ask the right question. Based on my 65,000 btu heat loss calculation, I'm wondering how long I can heat my house just on storage without adding heat. For example, a 600 gallon tank at 180 degrees.
  6. atlarge54

    atlarge54 New Member

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    If you can assume usable heat at 130 deg. 180-130=50 deg delta. 600galx8.33lb/galx50=249,900btu in tank or approx 4hours at 65k btu/hour. Are you an experienced wood burner? When I hear "I want to load once a day" alarms go off in my feeble brain. You've come to the right place for help, lots of brains in the boiler room.
  7. antos_ketcham

    antos_ketcham Member

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    How often you have to fire the boiler depends on many things. How much heat you are pulling, how cold it is outside, the efficiency of your home, type and quality of wood, etc. etc.

    I have found with my Greenwood 100 that I have to load it twice a day or every 8 to 12 hours. When it is warmer, say high 30's or 40's I can go with one filling per 24hrs.

    It really depends.

    Pete
  8. Eric Miller

    Eric Miller New Member

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    No, I've had my stove about six months so I'm still learning. It sure is fun though.

    Thanks again for the formula, that is pretty neat. So, I could theoretically heat my entire house for about 4 hours just from storage ... that seems pretty good to me. My 65k btu is based on 0 degree outside temperature, our avergae winter temperatures are usually much warmer - mid 20s to mid 40s. Also, I normally do not try to keep the entire house fully heated to 70.

    If I invest time and $ into this system I want to make sure I have realistic expectations on what it can do and how much work is involved. If I have to feed the boiler more then once a day on daily basis then it just isn't going to be pratical for me.

    Could a boiler like an EKO 40 recharge the 600 gallon tank from 130 to 180 on a single loading?

    At what water temperature does a water-to-air heat exchanger cease to be practical for a forced air system? Is 130 deg. about there?
  9. Eric Miller

    Eric Miller New Member

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    Pete, thanks. I can imagine there are a myriad of factors that influence how these systems operate. Living at a more southern latitude I'm sure will work to my advantage. It sounds like once-a-day loading is not unreasonable to expect as long as the system is sized and designed corrctly. I'm sure there would be days when I'd have to fire more then once a day, I just don't want that to be the normal daily routine.
  10. Nofossil

    Nofossil Moderator Emeritus

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    The 65k number seems a bit high to me. I heat 3500 square feet with a peak heat load about half that at -20. My actual average load is more like 10-15k per hour.

    Is this an existing house with some heating history (oil / gas consumption, for instance)?
  11. Eric Miller

    Eric Miller New Member

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    I've been told it seems high and told it looks low but I agree with you that it seems a little high to me. Of course, it is worst case right? And if one ton of HeatPump equals 12,000 btu then it seems to match up pretty close to my current and planned heat pump capacity.

    I don't have any real data to look back on. We've only been in the house a couple of years and last year I started a major remodeling project. I still haven't completed the remodeling so we are not occupying all the space yet but that will be completed soon I hope. The house originally had a 3 ton heat pump, it will be rezoned to just supply the basement and first floor. I have a three quotes to install a Heat Pump for the second floor. One quoted a 2 ton unit, one a 2.5 and the other a 3 ton.

    I noticed in Pete's post in this thread that he is a Greenwood owner. Some additional research I did today seems to be pushing me to a Greenwood so I've also started another thread soliciting input on the Greenwood units (http://www.hearth.com/econtent/index.php/forums/viewthread/16464/).
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