Results 1 to 9 of 9
  1. #1
    Join Date
    Jan 2006
    Posts
    32
    Just clocked my furnace over the past 6 hours. 4500 sq. ft. Stone faced ICF house, lots of south facing glass. Nicely sheltered from northwest winds.

    Todays conditions: 60 km/h WNW wind, 10 F. Cloudy. Snow and blowing snow.
    BTU required to keep house at 70.5F is 20.2 kbtu per hour.

    How's this compare with other calculated or measured values that people have ? Just curious how my house stacks up against conventional (or other designs) on this coldest day of the winter.

  2. #2
    Join Date
    Nov 2000
    Location
    Memphis TN USA
    Posts
    6,945
    How did you detirmine 20,000 BTU?

    Best to go to the source and clock the gas meter
    If the superheat ain't right it ain't charged right.

  3. #3
    Join Date
    Jan 2006
    Posts
    32
    3 ways.

    1. From the knowledge that it's a 59 kBTU gross output Buderus boiler.
    2. From the Gas meter.
    3. From the time it takes the air handler to cool the series buffer tank 24 F (which is the differential I am running on my Tekmar 262).

    The Buderus heats the buffer tankroughly 20 mins per hour on a day like this. That's roughly 20 kBTU. The buffer tank plus the water in the air handler coil, piping and boiler is about 45 gallons. Convert to pounds, see how long it takes to drop 24 F and you have another estimate. And of course the gas meter. Convert cu m to cu ft and use a 1025 BTU per cu ft number that the gas company uses.

    All 3 give me between 19kBTU and 21kBTU. Close enough.

  4. #4
    Join Date
    Nov 2004
    Posts
    2,927
    you are probably going to win the contest

  5. #5
    Join Date
    Jan 2006
    Posts
    32
    Originally posted by jacob perkins
    you are probably going to win the contest
    Yeah, perhaps. But I wish I could find a modulating boiler that would work for me. Anything out there is going to be effectively "bang-bang" at my typical winter space heating requirements of 8-10 kbtu per hour.

  6. #6
    Join Date
    Dec 2003
    Posts
    2,360
    Can you get a bigger buffer tank?

  7. #7
    Join Date
    Jul 2005
    Posts
    75

    Cool

    try looking at a munchkin boiler very eff 96%

  8. #8
    Join Date
    Dec 2005
    Posts
    117
    The smallest modulating boilers that I know of are the Munchkin T50 - between 16,000 BTU and 48,000 BTU output, the Lochinvar Knight KBN080 - between 14,500 and 73,000 output, or the Weil-Mclain Ultra 80 - between 14,500 and 71,000 output.

    Michael

    [Edited by aemeeich on 02-19-2006 at 12:43 AM]

  9. #9
    Join Date
    Jan 2006
    Posts
    32
    Thanks for the responses. The buffer tank is to prevent short cycling on my Buderus and allow outdoor reset modulated water temps all the way down to 85 F. If I had a modulating boiler that would modulate down to a few kbtu per hour, I wouldn't need the buffer tank. But as long as I need the buffer tank, I'll stick with the 9 month old Buderus which appears pretty bulletprooof.

    In general, we need at least 60kbtu for the indirect DHW for decent recovery times in the winter. In the summer, the solar preheat reduces that requirement. But the DHW requirement in the dead of cloudy winter set's the minimum size boiler unfortunately. But we need no more than 20kbtu and more typically 8kbtu for space heating. It's almost like we need a 2 stage boiler, where the lower stage is modulating from 2-20kbtu and the higher stage is for DHW when needed.

    Somebody get on that, would ya !?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event