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Community and Q&A

Heating load vs. electrical load … all ends up as heat anyway?

jinmtvt | Posted in General Questions on

Would like to debate about the fact that most ( read all ) of our electrical energy usage ends up as heat during heating season, and thus cannot be accounted as for seperate expanses from the heating loads.

I read alot about watching all small electrical loads from mini appliances, chargers etc..
Water tank standy heat losses .. computer let turned on all day long.

But during heating seaons, doesn’t it all gets convereted to heat at the end ??
Ok we might loose some light energy through windows, some excess heating could end up being generated during daytime if SHG is high enough already etc…

Water heater tanks with ~100w standby losses cost in the vicivnity of 90-100$/year of stanby power,
but during almost 50% of my local climate time, it all ends up heating the room where the tank(s) are located.

computers are fairly efficient at converting 80-90% of their energy use as direct heat

Wanted to point that out for some who might worry about all the losses,
worry about them during cooling season…else focus on something else 🙂

( in hope i am not wrong on the situation .. )

Also some product manufacturers are using their product consumption reduction to advertise yearly saved costs, but never take into account that in some sitation, 50% of the savings need to be cut off, bringing the payback terms to double ..which is not something to take lightly

example … lighting industry
LED VS CFL VS INCAN … i am all for LEDS ( i personally only install LEDS on all new )
But the advertised paybacks are completly off ..

a 100W incan puts out what..90W of heat ??? and even most of the light output ends up as heat when getting absorbed by difference surfaces … so an equivalent 20W cfl /10w led
uses less energy … but does not contribute much to the heating load

in most of the northern climate this has a pretty large impact on payback because lights are usually on only when dark, where heating loads are higher.

my 0.2 kw/h 🙂

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  1. davidmeiland | | #1

    Right. In heating climates, waste heat contributes to space heating part of the time.

    It's an issue during the non-heating season, and a bigger issue in cooling climates. In parts of the southern U.S., air conditioners are already on, and in some places they never go off.

  2. GBA Editor
    Martin Holladay | | #2

    Building energy modelers have long understood the fact that waste heat from electrical appliances and lighting (internal gains) reduce a building's space heating needs while increasing a building's cooling needs. This is not news.

    Of course, not all electrical loads occur inside your thermal envelope. Exceptions include outdoor lighting, well pumps, sewage pumps, and garage door openers, among other loads.

    Using your electrical loads to heat your home isn't particularly efficient. You get the same efficiency as electric-resistance baseboard heaters. You'd be better off heating your home with a ductless minisplit than with 100-watt incandescent lightbulbs.

    And if your home has an air conditioner... all those electrical appliances work against you during the cooling season.

  3. jinmtvt | | #3

    Martin : i wans't implying of using it for heating !! :P
    and i know it is not news, only wanted to point it out because i haven't seen a single mention of it here,
    and some are still discussing about losses from all electrical usage and using it for calculations.
    I believe that a difference in the "double" is an important one when considering paybacks.

    Also, do you not HEAT your garage ?? :p

    David Meiland: AC already one ? phew ... at least it costs much less than heating with current mini splits equipement and the detalT difference.

    i'm sorry if i sounded like i was announcing something new..was not my intent... :p
    wanted confirmation and pointing out to the ones that might not have included it in their works.

  4. GBA Editor
    Martin Holladay | | #4

    You wrote, "I haven't seen a single mention of it [internal gains] here."

    A few examples:

    Comment by Michael Blasnik: "The use of base 65 for heating degree days was developed decades ago when internal gains were much lower and buildings were less insulated than they are today. It has only stayed in existence due to momentum. Internal gains (solar, plug/appliance, and occupants) typically provide about 10F in "free heat" (aka temperature float)."

    Michael Blasnik: “If you are building super-efficient homes, the heating usage will be dominated by hard-to-model factors, including internal gains like light bulbs and plug loads.”

    Martin Holladay: "Internal heat gains are generated by pets and people (who emit body heat and moisture), lighting, electrical appliances, and combustion appliances (like kitchen ranges and water heaters) located inside the building’s thermal envelope. ...Energy-efficient appliances and lighting produce less waste heat than inefficient appliances and lighting."

    Martin Holladay: "While cold-climate designers have to worry about heat escaping from the envelope in all directions, the heat-gain concerns of hot-climate designers are overwhelmingly dominated by just three major factors: windows, ceilings, and internal gains."

    Comment by Doug McEvers: "Internal gains are not what they used to be with cfl's and higher efficiency appliances, unfortunately this is often offset with a house full of electrical gadgets."

    There are lots more references to internal gains on this site.

  5. jinmtvt | | #5

    ok well i guess you guys mention internal gains often then,
    but i was more reffering to the implcations it has toward calculus and paybacks.

    i stand corrected :p

    ( do we delete the threa now ? hahaha )

    So during heating season, can someone use the total ( or near total ) electrical bills to report heating loads ( if no other heating sources ) ??

    We often read about using load meters on the heating appliance(s) , but it then does not take into account all of the remaining electrical loads generated heat.

    Probably has less of an impact on houses with minimum insulation , but on high performance
    buildings, the % of the gains grow larger toward the heating appliances use ?

    How could one calculate possible internal gains while in design stage ?

  6. GBA Editor
    Martin Holladay | | #6

    Q. "How could one calculate possible internal gains while in design stage?"

    A. Here is some information from one of my articles: "Internal loads can be significant in homes and must be calculated. The sensible heat gain (body heat) emitted by one occupant is usually assumed to be 230 Btuh (67 watts). The default assumption for a home’s appliances is usually 1,600 Btu/h (469 watts); lighting is assumed to add another 1,600 Btu/h (469 watts). These default assumptions can be adjusted up or down if necessary. If a house has an unusual number of appliances or equipment — for example, a home business that includes a computer server room — internal loads will be higher than these default assumptions."

    More information here: Calculating Cooling Loads.

  7. jinmtvt | | #7

    Ok super will read through this later ...

  8. Expert Member
    Dana Dorsett | | #8

    I'd like to see the data behind Blasnik's assertion:


    Comment by Michael Blasnik: "The use of base 65 for heating degree days was developed decades ago when internal gains were much lower and buildings were less insulated than they are today. It has only stayed in existence due to momentum. Internal gains (solar, plug/appliance, and occupants) typically provide about 10F in "free heat" (aka temperature float)."


    Maybe in a house with 3Tivos and a collection of game machines and all-incandescent lighting, or in tight, higher than code house would the balance point be 10F below the heating setpoint. (Sez, me, my gut, and 25 years of unlogged but measured heat loads using the nameplate efficiency of the space heating equipment. :-) ) Base 65F is still pretty close to reality in any house that I've actually tracked, (or at least closer to 65F than base-60F).

    But my view on that could be moved by actual field data, (models don't count, unless vetted by real world measurements.) Heat load calculation tools are still pretty crude, but fuel use per HDD base-65 seems to track within a 5% window over a wide range of heating season outdoor temperatures, for most houses. (Moving to base 60F wouldn't work at all in my house, but we're not power-pigs compared to the average, nor are we at current code-min.)

    Mind you the heating load offset by power use is typically ~3x as expensive as the heating fuel it displaced at typical MA fuel pricing & efficiency.

    At 15 cents/kwh electricity you're getting about 22,750 BTU/$ .

    At $1.25/therm gas in an 80% efficiency cast iron pig of a sub-code-legal boiler you get 64,000 BTU/$ of heat into the home. (Condensing boilers do better, at ~76,000BTU/$)

    The cost of pumping that sensible heat out with crummy window air-conditioners during the cooling season is about 1kwh to every 3-4kwh of plug load too, and that's not free. (With high efficiency mini-split cooling it's a heluva lot less of a burden, maybe 1kwh for every 6-8kwh of plug load, at New England summertime outdoor temps.)

    The "payback" on heating energy offset from plug loads is really piss-poor, and does not significantly reduce the payback of higher efficiency lighting etc. If every buck of plug load only offsets 35 cents of fuel use during the heating season and adds 25-35 cents of cooling power during the cooling season, it's a measurable factor, but doesn't change the basic equation. It's a not-very high secondary factor.

    But run your own spreadsheet model on your real heating fuel, utility rates & heating/cooling efficiencies, since clearly YMMV. (In some places resistance electricity is on par with condensing propane for the heating season.)

    BTW: A 100W incandescent puts out nearly 100% of heat. Yes, something like 10% of the energy escaped the bulb as visible light, but only a small fraction of that light escapes the HOUSE before being absorbed by the surfaces it reaches. Even when the incident surface is a window, a good fraction of that is reflected back into the room. Unless you live in a clear-glass house, light leakage out of the windows that was more than 10% of the light output (==1% of total energy dissipation) would be rare. Call it 99%. (But so what? It's still wicked-expensive heating, and a 340BTU/hr cooling load.)

  9. user-1135248 | | #9

    Another exterior load to think about is HVAC compressors. They
    have a little overhead when running, but that's not all. Modern
    systems generally include some way to keep the compressor warm even
    when it's not running, either by resistance heat or using the inverter
    drive to bleed a little "waste" current through the motor coils in
    standby. My 1.5T Daikin uses on the order of 2 kwh/day or a little
    less than 100W just when it's sitting there "doing nothing". Even
    though the compressor is wrapped in a cozy little blanket, it's
    still trying to heat the outdoors. The top of the unit housing
    makes a nice bright spot on the IR camera...

    But aside from that and the aforementioned pumps and lights and
    EV chargers and whatever else might be outside the envelope, in
    theory every kwh that comes into the place eventually turns into
    heat. Reading your own meter and/or examining electric bills,
    coupled with creative turning-off of exterior loads during known
    periods, can help calculate how much.


  10. nvman | | #10

    I know that two 60 watt incandescent bulbs can heat up a small bathroom pretty quickly. At -20 C, our inefficient home cools off pretty quickly especially when you set the temp back to 16 C but those two bulbs allow me to get ready for work at 5 AM without having to turn up the heat while the rest of the family sleeps in until 7 AM.

  11. jinmtvt | | #11

    AARON : man you are a "cheap" dude :p
    my main bathroom as heated floor and i leave it at ~23C at 42"h ... it costs..but i love it :)
    only 1 life, comfort comes first in bathrooms... ( if u can afford it of course )

  12. user-943732 | | #12

    I'm a little surprised that you think HDD65 is still a good estimate. The problems with HDD65 were noted back in my `989 edition of ASHRAE Fundamentals which includes degree day correction factors to use when doing calculation based on HDD65 due to base 65 no longer being very good. If you just do any sort of rough calculation for how much temperature float you should expect in a typical home, I think you'd find a number between 8 and 15F. Now if you keep your thermostat at 72 and have low plug loads then HDD65 might be a good estimate. But not for the typical home.

    But you don't need to trust any sort of modeling or calculation, I've done some analysis of utility bills where I statistically find the best fitting degree day base based on the billing data and weather. I've done this for a fairly large number of homes around the country -- mostly when evaluating energy efficiency programs. I keep finding that, in heating climates, the best fit to degree day base is typically around 60F. I find slightly higher values (e.g., 62F) when looking at low income housing stock and other high use homes. I find lower values (56F-58F) when looking at newer or higher efficiency homes.

    I just poked around some on my computer and quickly found the following datasets that include statistically derived HDD base temperatures.from billing data:

    1) Entire residential customer base of mid-western gas utility: 1.1 million customers, average HDD base = 60.4, just 15% were >=65F

    2) Another entire gas utility in Mid-west:, average HDD base= 59.6 in 650,000 homes

    3) two retrofit evaluation studies in the Pacific Northwest: 59.6F in 6,700 homes for one program, 58.7F in 15,000 homes for another program

    4) low income weatherization study targeted at high use homes in the mid-Atlantic: 63.8F in 1000 homes. As expected, if you focus on poorly insulated high use homes, you start to get closer to the 65F degree day base.

    5) More low income weatherization studies-- Mid-western statewide: 62F in 2200 homes, Mid-Atlantic utility: 61.1F in 6500 homes, Mixed-Humid Southern utility: 62.6F in 21,000 homes, Rocky Mountain statewide: 59.4F average from 38,000 homes.

    6) new home study in Mid Atlantic: 59.8F in 120 homes -- somewhat higher than I would expect for new homes, but still around 60F.

    7) Hot Humid climate new homes (gas heated): 64,7F in 30,000 homes. It's only in hot climates where i find HDD base temperatures near 65F often. I have other data to indicate that people in hot climates set their heating thermostats much higher than people in cold climates -- they aren't used to the cold and it's inexpensive for them to keep their homes very warm.

    I've got many more studies to go, but I think this demonstrates my point fairly well. If your home's heating use fits much better at HDD65 than HDD60, then I'd guess you either live in a hot climate or else you have some combination of a high thermostat setting, low internal and solar gains, or inefficient home. I'm wondering how you estimated your own HDD base temperature?

  13. user-1135248 | | #13

    So is the float basically from the electrical base load? Does
    it also stem from solar gain [thus implying that when one is
    tracking HDDs, one should also track how sunny/windy/etc each
    day was]?


  14. user-943732 | | #14


    It's waste heat from electric use plus solar plus waste heat from gas baseload (hot water, cooking) plus occupant body heat plus any other regular source of heat input to the space that doesn't come from the heating system.

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