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Did a heat loss.....does this seem right

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by MaverickM23, Feb 15, 2013.

  1. MaverickM23

    MaverickM23 New Member

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    Following others advice on here I downloaded a program and did a heat loss calculation. I used the slant fin software. Put in all of the data to the best of my knowledge. My home is a 1950 sq ft main floor, with an 1885 sq ft basement with poured walls, built in 2003 living in Central PA. I used the average temp we had this year in January which was 28 degrees and I got a heat loss of 52,989 an hour. My question is does this seem right? I also calculated the fuel I used in January to February, 200 gallons in 36 days, and from that using 139,000 BTU's per gallon found that I used 32,175 an hour. I know some days were colder than others but is my figuring correct. And also if this is my heat loss how do I apply this to boilers I am looking at?

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  2. maple1

    maple1 Minister of Fire

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    What do you have for a boiler now - and what is its rating?

    I didn't do any heat loss number crunching at all when I decided on my new setup. I just tried to find out as best I could what my old boiler did on wood (which was pretty +/-, I couldn't find any wood rating on it and pretty well only guesses at it), and my new one was double that. And I think maybe 50% more than my old ones rating on oil. That was good enough for me. Then with storage able to take any extra heat, I figured I was pretty safe. It's worked out even better than I was hoping for - the house has been warmer than it ever was and I think I'm only burning half the time than with the old one.

    There was a heat loss done on the house 17 years ago when we built, but I have no idea what it came up with or where it is. I think the heating guys kept it back then. I just knew that the old boiler could satisfy it on wood (barely), and with room to spare on oil (if you kept the oil truck coming).
  3. MaverickM23

    MaverickM23 New Member

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    According to my boiler Im running at 130,000 BTU per hour with a net of 113,000 per hour, I think according to the website for EFM. Im running an EFM VT1000E with a 1.00-80 H nozzle.
  4. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Wow, just my two cents but that seems to be way oversized heating system. My heatloss on around 1250 sq ft is 40000 btu/hr at -40 with a full finished basement kept at the same t-stat set point as the main floor. At around 53000 btu/hr loss in your climate you could probably derive some quick ROI on insulation upgrades. AFA is this accurate, folks will need more info on home construction window size & type, insulation values etc to give you a reasonable estimate of the accuracy of your heatloss calc.
  5. ihookem

    ihookem Minister of Fire

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    This is just my opinion though, but 32k btu per hr doesn't seem too bad for January. A lot of things matter like your temp in the house. 66* will use a lot less than @ 72*. High ceilings, cathedral, on a hill top, kids leaving doors open, bath fans, ect. have an effect. For a 2003 home 32k btu seems a bit high though. My home is 2200 sq.ft ranch / 9ft. ceilings and believe I use about 20k when it's about 0* When it's above 32 and sunny my furnace doe not come on for a few hours @ 66*.
  6. maple1

    maple1 Minister of Fire

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    Just my off-the-cuff opinion, but that sounds like more boiler than you need.

    Mine was rated at 107,000 BTU on oil, using a Riello F5 with .75x80 nozzle. I was guessing that on wood it didn't put out much more than 70,000 BTU. I'm now using a 140,000 BTU wood boiler that heats my house with ease. House is 18 years old, 2700 sq. ft. in two stories over a 1500 sq.ft. basement - which I would expect to have a bit more heat loss than yours just from their configurations & ages.

    Kinda wish I had my heat loss calcs from 18 years ago, although doesn't really matter much now.
  7. MaverickM23

    MaverickM23 New Member

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    I tried to follow the heat loss program the best I could and enter the correct values. My basement isn't finished it is just 10 inch poured walls. The house is built into a bank so three sides are below grade. It does have rather large windows, most of them being 62 inches tall and the house is on top of a hill that the wind really blows at. I figured the more accurate would be the actual fuel I used. I keep the house at 58 degrees expect for one zone that is programmed to go up and down when Im there. January was very cold here, not -40 but did get to 0 or below a few nites. Im not sure the numbers on my current boiler are right there are a bunch of BTU values on it. Also I used 139,000 as the value of a gallon of oil, but then read that most boilers will only net 115,000 based on efficency, is that right?
  8. MaverickM23

    MaverickM23 New Member

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    Im thinking it might be. By the way how do you like your Varm 40? I have been in contact with smokeless heat and they recommended the Vedolux 37 for my house. I was thinking about going with them and a 500 gallon storage tank
  9. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Yep thats right, tough to get oil anywhere near nat gas or propane. Not enough water in oil to condense out for that last bit of gain in eff. Good oil burners may get high 80's.
  10. MaverickM23

    MaverickM23 New Member

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    Well then I used about 25,000 BTU an hour in January if I figure it on what I actually used.
  11. STIHLY DAN

    STIHLY DAN Feeling the Heat

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    When you do a heat loss calc. You need to use the coldest temp you may get. That should have been an option in your program. PA should be around 0. Also oil has 144,000 btu's per gallon. With an average unit running 85 %. Your basement is your big heat loss. Would you be heating that area? If not, redo your calc with out it. If you are, time for some insulation.
  12. MaverickM23

    MaverickM23 New Member

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    I will be heating it, just not as warm probably as the upstairs. I could see in my program that the basement was my major heat loss. But if I get the right sized or slightly larger I will keep it warmer too. Im just trying to figure out what size BTU's I need to be looking for in a boiler. Im planning on going with at least 500 gallons of storage as of now but maybe I should go 1000 and just get a larger boiler. There is another building, a shop right beside it that I might try to heat in the future.
  13. VT_Bubba

    VT_Bubba Member

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    Maverick,

    I read a lot about suggested heat loss calcs on this forum, which makes total sense on new construction and complete house remodels.

    When you are just replacing a boiler, the real issue is what radiation you have installed in the house. The Heat Loss calc's are used to size the amount of radiation required to heat a given space, but I'm not sure that calculation makes much sense on a boiler replacement. If your existing House Radiation (BaseBoard and DHW) is staying the same, I would add up your existing radiation and then calculate the Max BTU's needed to support that radiation loading.

    In my case, I have about 2000sqft, living in VT where below-0 is very common. I have 2 Heating zones (60ft and 40ft of BaseBoard) and my Indirect DHW Tank, which get's priority over the heating zones. So my Max Boiler loading is 100ft of BB at approx 600BTU/ft=60,000BTU Max Boiler load. The DHW could consume another 30,000-50,000 BTU's, so without priority control I would need (60K + 50K = 110KBTU's) to handle my max heating load. With the priority control on my DHW tank, and 100ft of BaseBoard, the most my house could ever consume from ANY boiler is 60,000 BTU's (regardless of the house insullation or temperature outside) !!! Buying a larger boiler without water storage, will only cause short-cycles on the boiler and lower your overall efficency ! So, I purchased an 80K-BTU boiler (larger for future expansion), and then down fired the Boiler with a 0.5gph nozzel = 60K BTU's. The 60K BTUs heat my 2,000sqft house better than my old 110KBTU Boiler with the DHW Coil, and my energy costs have gone way down.

    Also, when you calc BTU's of needed Heat, you need to consider the boiler efficency. Real BTU's of Heat = 139,000 BTU's/gal x 0.85 boiler efficency = 118,000 BTUs of usable heat energy.

    In summary, Heat Loss Calc's are not as important for boiler replacements, when the radiation stay's the unchanged. If your existing house radiation services your home heat loss OK, then just calculate the Max BTU Load your boiler will ever need to service at one time,using your existing radiation that is installed (using 580-610 BTU\ft for Base Board). Make sure you include any DHW loading too, if DHW is required when all heating zones are in use.

    Just my humble opinion, which has worked well for me at my house (110K BTU boiler was replaced with a 60K BTU Boiler).

    VT_Bubba
  14. logger6644

    logger6644 New Member

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    Hi, I'm a mechanical engineer and I can tell you that heat loss calculations are very tricky, too many variables. Wind exposure, air changes non-uniform insulation, etc. Just treat the calculations as ballpark. Your oil burn is probably a better estimate, but since efficiencies are involved, I'd round it up to 40K per hour average. Since you are using a 40 degree delta T (28 to 68) you may want to make that 50 degrees or use a 50K per hour design rate. Most 100K rated boilers will actually give you in that ballpark for 8 hour burn, as they rate them for peak output not average output. People that like a lot of storage may want to oversize the boiler, and park all that extra heat in the storage so they don'[t have to tend the unit as often. So besides the heat loss calculations you need to decide what kind of system you want to put together.
    Taylor Sutherland and heaterman like this.
  15. heaterman

    heaterman Minister of Fire

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    Good answer here.
    Taylor Sutherland likes this.
  16. rkusek

    rkusek Minister of Fire

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    +1 on using it as a guide. The slant fin came up with 35k btu for my main floor (2200sqft) and about 30k for the basement also with has 2 sides above ground for a +10 F degree design day. The backup electric heat only has a 15k btu of strip (~50,000 btus) which one would think would be sized for worst case scenario. FYI, I can keep the home at 70 and a 30x60 pole barn at 65 for 8 hrs with a load of good wood in my EKO40 during single digit cold weather when the barn is already up to temp. If the barn is cold (~45F) or so the load will burn out in about 5 hrs. Bottom line is the heat loss calcs for me seem to be worse than worse case.
  17. slowzuki

    slowzuki Feeling the Heat

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    Err, its not the water in the fuel that a condensing boiler is condensing, its the water produced by burning the fuel with air. Gas fuels are clean enough to do this with reasonable materials. Oil can't burn clean enough, the condensate is too aggressive for conventional materials.
  18. Frozen Canuck

    Frozen Canuck Minister of Fire

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    Good catch Slow, my bad.

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