Run time vs right-sizing

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At -10C, which is also my design temp, my condensing gas furnace runs for 20 mins every 2 hours to maintain a setpoint of 18C with a spread of .5C, obviously it is theoretically oversized, however, if sized 'correctly' it would run continuously at -10C and use significantly more KWH's. Which would be the better scenario, almost continuous run times to improve comfort at the expense of higher electricity usage or the shorter cycles with less wear on the blower and draft inducer fan?
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wrote:

WRONG! If it were sized correctly, it would have longer run times using a smaller KW heater. Thus balancing out the electric consumption. It is always better to properly size a furnace. Bubba
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There are no heat strips in this application - gas only. A smaller furnace would cost more to operate and maintain due to much longer run times. 20 min run times are certainly not short cycling nor reducing the efficiency of the furnace.
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Interesting how you "use significantly more KWH's" as you point out. KWH's would be Kilo-Watt-hours. Those would be electric numbers junior. A smaller furnace would NOT cost more to operated and maintain. 20 min run times per 2 HOURS at design temperature IS definately over-sized. You're an IDIOT and/or TROLL. Bubba
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You are either uneducated, misinformed or both.
Let me expand on "Those would be electric numbers":
KWH is a standard symbol representing power usage usually in the form kWh which is 1000 watts used for a period of 1 hour. If the smaller furnace has a 1/2 HP motor drawing 4A it will consume 1452 kWh in a 6 month heating season (4*120*24*30*6*.7/1000) with a 70% duty cycle whereas the larger furnace will consume only 207 kWh with a 10% duty cycle. At 20cents/kWh the difference will heat my home for 4 months. This does not even take into consideration the inducer fan or increased wear and maintenance costs.
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You've forgotten the fan laws. A smaller furnace will move less air. If you take a given motor and move 1/2 the air that motor will use 1/4 of the electricity. Since you're putting less heat into the air it takes fewer CFM to move the heat.
If you move to a modulating furnace with a variable speed the numbers drop further. Or better yet move to a mod/con boiler with constant circulation and the electricity consumed is less yet.

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Nope. Neither. Let me help you out just a bit. In the world of heating and cooling there are two different worlds: One, happens to be the world you live in. Its called the "Labratory World". The other world happens to be called "The real world". That happens to be the world I live in. If you even remotely think the difference in those two furnaces will heat your home for 4 months for free (compared to the smaller one) then you need to put your tinfoil hat on and go out in the middle of a busy highway and lick a window in your diapers. You can quote all the numbers you want. It just "aint" goina happen. Get it sized right and get it done the first time. Bubba
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I'd prefer a longer run time. So the heat doesn't all dump into the home at once. As you have only a half degree temp swing, you've aparently got good insulation, though. You could replace the furnace, and see if it's more comfortable next year. And then consider put the other one back.
Let me guess... you're an engineer?
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Stormy, try to be original

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I don't remember ever hearing that advice. Please remind me.
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You mean "Let me guess....you're an engineer?" that's what I was referring to. that's been said by at least 2 guys already including Bubba.
Some guys tease you because they know you are an idiot. I don't know enough about the trade to know you're an idiot for sure, but it sure sounds it.
I tease you because I enjoy it, and I am doing it just in fun, no malice intended. Tease me back on something. hey, check out my name!
Anyway, I don't know what made Bob Loblaw mention your religion, but I do agree with him. You mention your religion in every post and say stuff that the experienced trades people think is stupid. That is not good.
Enjoy your evening Chris
DIMwit

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You mean "Let me guess....you're an engineer?" that's what I was referring to. that's been said by at least 2 guys already including Bubba. CY: oh, that! Yeah, that's not original. Sorry about that.
Some guys tease you because they know you are an idiot. I don't know enough about the trade to know you're an idiot for sure, but it sure sounds it. CY: Well, hang around me for awhile and you'll find out after awhile.
I tease you because I enjoy it, and I am doing it just in fun, no malice intended. Tease me back on something. hey, check out my name! CY: Thanks, I'll do that some day.
Anyway, I don't know what made Bob Loblaw mention your religion, but I do agree with him. You mention your religion in every post and say stuff that the experienced trades people think is stupid. That is not good. CY: Only cause it's in my screen name. Can't remember mentioning my religion in a long time on this group. OK, so the trade guys think I say stupid stuff. Many times they flame the home owners, call em names, and tell em to go call someone qualified. I havn't kept score, but I'd have to guess that half to two thirds of the replies on this group contain no useful information beyond "call a repairman". At least I'm trying to answer their questions.
Enjoy your evening Chris CY: Thanks. I'll keep you posted. Going out to visit some friends. One elderly lady in the old age home, a friend and I visit her on a regular basis.
DIMwit
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Yeah, the old ones will let you cop a feel and not complain, especially if they are in a coma.
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Oscar,
you know, I was going to say something mean like that, but I had a moment of compassion. Glad it was said. LOL. Actually, ROTF-LMAO
Bob
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One of the rare moments when I mention religion on this NG. Last night another fellow and I went to the nursing home. She had some family visiting. We chatted, and met some folks. We brought bread, and sacrament cups. Got some water there. Blessed and passed the sacrament for her. Guess that my nursing home is a lot less exciting than yours.
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On Thu, 07 Dec 2006 14:33:24 GMT, "Stormin Mormon"

Let ME guess......... Stormy is a clueless twit. My crystal ball told me so. Bubba
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Bubba posted for all of us...

My magic underwear told me I have it on backward.
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Vance wrote:

You make similar decisions/tradeoffs when choosing between a pickup truck with a 4 cylinder engine or an theoretically oversized 10 cylinder engine... some people like the short cycle, other don't, regardless of the energy cost, it's whatever you prefer.
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Troll

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