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Heat Loss Calculations

Post in 'The Green Room' started by jeffesonm, Nov 25, 2013.

  1. velvetfoot

    velvetfoot Minister of Fire

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    Shouldn't the existing or maybe a new wood stove keep up with that? Could a boiler be overkill, or is it distributing the heat over the 1800 ft2?

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  2. DBoon

    DBoon Minister of Fire

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    Yes, very true. I'm in a Central NY state of mind where 45 degree cellar temps is the norm when the temps get to 0 degrees F.

    Yes, I agree. From yearly usage, it is easy to check the calculations. If the base outside temperature is 20 degrees F, and the interior is 65 degrees F (just to make it a round number, and since this is what Heating Degree Days are based on...), then the difference is 45 degrees.

    Then, if you calculated ~50 kTBU/hour with a 20 degree outside temperature, you could then assume that this situation existed for an entire day - that would be 65-20=45 degrees for one day (i.e. a HDD), and 24 hours * 50 kBTU/hour for the same day (or 1.2 million BTUs). The OP could look up the HDDs for last year for his location at heatingdegreedays.net (let's say it was 5000, as he indicated earlier). Dividing 5000 HDD by 45 HDD = 111, and multiplying 1.2 million BTUs by 111 = yearly heating season BTUs (in this case, about 133 million BTUs).

    If the OP burned 1000 gallons of oil at 140,000 BTUs/gallon at 75% efficiency, that would be 105 million BTUs. If the OP plugged in actual HDDs and oil consumption with boiler/furnace efficiency (use about 70% for an old unit, or 85% for a newer unit), he could back-calculate to get his BTU/hour heat loss based on last heating season's oil consumption and some reasonable assumptions about furnace/boiler efficiencies.
  3. woodgeek

    woodgeek Minister of Fire

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    The OP reported that the previous owner used 1100 gallons for heat, DHW and summer standby. If we assume 900 gals were heat, that works out to 33 kBTU/h at his average daily mid-January temp of ~30°F.
  4. jeffesonm

    jeffesonm Feeling the Heat

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    Thanks for the additional input guys, we do seem to be converging here. Running a separate calc for the floors makes sense... the basement usually cruises at mid-low 50s in the winter. Last year I also had the oil boiler idling away and making DHW... just put in a GeoSpring HWH and the basement does seem a bit cooler without the boiler running, but it could just be me. One of these days I will order some more temp sensors and get the Arduino logging all of this stuff. I also looked at 2011 on wunderground and got a annual HDD of 5400, although this seems less important than the design loss given my nearly infinite supply of firewood.

    I have lived in the house one full year (plus some) but installed a wood insert right away, so I never got a chance to measure a full year of straight oil usage myself. As per the oil company who serviced the previous owners account, he used between 1000 and 1200 gallons/year. Last year with the insert I had the 275 gallon tank filled twice for about 450 gallons total. Most of this was used for DHW and standby, but during the coldest periods the boiler would kick on around 4-5 AM and circulate through the baseboards for a bit as the insert died down and I was asleep. Once I reloaded the baseboards would stay off until the next morning. Keep in mind the thermostat was set to 55 to use as little oil as possible... during the days the stove kept the house in the mid/high sixties but overnight it just couldn't keep up.

    From last year's experience the Matrix did a good job keeping the house from getting too cold. We saved a lot of oil, almost enough to pay for the stove, but it would be a real stretch to say it was warm and cozy. The new Jotul F55 definitely does better which I'm sure is a function of the bigger size and freestander vs flush insert. It radiates more heat, which is nice, especially when the fire dies down overnight and it's just coals in the stove. Closing off an unused bedroom door also bumps up the master bedroom temp by a degree or two. I feel like the stove upgrade has bought me a few more degrees of comfort.

    This past weekend I hosted 40+ people for a party at the house. I didn't want to fuss with the stove so I turned back on the oil boiler for the weekend (and was pleased when it all still worked!). Even with the thermostats set at 65, I was really impressed by how nice and evenly warm the house felt when heated from the baseboards.
  5. DickRussell

    DickRussell Member

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    "This past weekend I hosted 40+ people for a party at the house."

    Wow, at around 100 watts of heat output per adult, just sitting around (dull party), that still would give you around 18% of your heat load (75K at 20 F), a nice reduction. Crank up the music to get them all dancing vigorously, and you're at over half the heat load; not bad (what's the $$ tradeoff between heating oil and beer?). In some houses, 40 people dancing at a winter party would mean some windows would be thrown open.
  6. jeffesonm

    jeffesonm Feeling the Heat

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    Ha! It was a post-Thanksgiving turkey [plus everything else] deep fry party... with 40+ people at moderate activity plus the oven, and two table top fryers, there were quite a few windows open.
  7. jdp1152

    jdp1152 Minister of Fire

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    Unless you've tightened the envelope up, 1 air change in 1957 construction is way off. Even with a lot of DIY effort I've read where 1.5 is about as reasonable as you can expect without a deep energy retrofit. I've busted my back side and got to 2 on 1953 house.
  8. woodgeek

    woodgeek Minister of Fire

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    I'm gonna disagree with this one. I bought a drafty 1960 split level, and have been estimating its ACH_nat through a combination of heat loss calcs (like upthread), humidifier water demand, and most recently, actual blower door. I started out (no airsealing) around 1.3-1.5. A weekend of cleaning up the weather stripping on the 1960 windows (and adding v-strips) dropped me to ~1.0. Sealing all the 'big holes' in the attic (plumbing vent, open cavities, interior chimney) got me to ~0.7. Sealing most of the top plates (the ones I could reach under a 5/12 roof) got me to 0.5 (this verified by blower door). Calling in some pros who spray foamed the last top plates in the attic, and who airsealed ~70% of my rim joists with densepak cellulose (the rest is inaccessible) got me to ACH_nat < 0.3 (again, blower door ACH50 = 4-5). If I go any further, I would need to power-vent. As it is, we crack a window 24/7 in the shoulder seasons for fresh air.

    DIY time, maybe 50 hours total.
    Contractor charge for final airsealing: $1500
    NOT a deep energy retrofit.

    Going from 1.3 to 0.3 ACH_nat reduces the seasonal heat loss in my climate by ~35 Million BTUs. With oil heat that would be ~$1200/year in savings.
    Frozen Canuck likes this.
  9. TradEddie

    TradEddie Minister of Fire

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    Can you suggest one of these, I've been looking for one at a reasonable price?

    TE
  10. woodgeek

    woodgeek Minister of Fire

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    Something like this.... http://www.amazon.com/Hour-Meter-120-AC-Volts/dp/B0027NLO8K/ref=pd_sim_hi_1

    or this: http://www.amazon.com/Ostart-Electr...ronic-Counter/dp/B00BKWAY62/ref=pd_sbs_misc_1

    I hooked it across the 120VAC burner motor so it counted burner run hours. With a 1.1 gph nozzle, gallons used is just 1.1*hours, of course. Not resettable, so I had to keep a written log sheet nearby.
  11. velvetfoot

    velvetfoot Minister of Fire

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    My ecobee thermostat and I'm sure others, tracks runtime.
  12. TradEddie

    TradEddie Minister of Fire

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    Thanks, I was thinking of something more complicated, at work I use dataloggers costing tens of thousands of dollars, so I never thought about something so basic. One of these will likely be added to my next amazon order. Better yet, I see low voltage versions I could wire through my thermostat or now unused humidifier contacts. Unfortunately I should be in the region of diminishing returns with my air sealing and insulation, so I won't see much benefits.

    TE

    Edited when I realized the thermostat and humidifier are 28vac.
    Last edited: Dec 5, 2013
    woodgeek likes this.
  13. woodgeek

    woodgeek Minister of Fire

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    Yar. For me I found them useful for tracking standby oil usage during summer vacation, and added usage from DHW, etc. With the boiler scrapped and a logging stat on my HVAC, my 'hour meter' is now sitting in a drawer.
    Last edited: Dec 7, 2013

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