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New approach to furnace sizing?

AlanB4 | Posted in Energy Efficiency and Durability on

Here is something i just heard about, i wondered the expert’s opinions, the page is gone so the internet archive version is linked

http://web.archive.org/web/20130628061152/http://www.cmhc-schl.gc.ca/en/co/renoho/refash/refash_018.cfm

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Replies

  1. charlie_sullivan | | #1

    I think that using measured fuel consumption as described there has the potential to be much more accurate than using Manual J or approximations to Manual J. Some problems are:
    1) Knowing the fuel use for other purposes such as hot water heating. You can guess that that's independent of outdoor temperature, and use the summertime fuel consumption rate, but it's hard to be sure--for example, do people take longer warmer showers in the winter to warm themselves? Or do they shower more frequently in the summer after getting hot and sweaty or going swimming?
    2) In that example, they somehow jump from 40% oversizing is permissible to concluding that 40% oversizing is a good idea. How oversizing matters varies with the type of system, but better would be to say that the range of good size choices is from 100% to 140% of the calculated load, with the bottom end of that range preferred.

  2. GBA Editor
    Martin Holladay | | #2

    Alan,
    The described method of furnace sizing is certainly useful, and is usually more accurate than the typical Manual J calculation. However, the method is not a "new approach."

  3. AlanB4 | | #3

    @Charlie, I agree you have to subtract other usage, if you have nothing else gas then no correction would be necessary, many places i have lived in have only a natural gas furnace, some have natural gas hot water, and even fewer have natural gas stove (and i've yet to see a natural gas dryer in the wild though i know they are available).

    @ Martin, your correct, i should have worded the title better, its new to Alan ;)
    I was trying to ask is it an accurate method which you answered, thanks

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