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Old 12-16-2010, 12:14 PM   #1
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Furnace size required for 1100 sq ft house.


Hello,

I have a slight concern and would think this forum can answer my question since you all have a lot of experience with furnaces.

My question is what size of furnace is required for a 1100 sq ft house with R12 walls (basement and upper level) and R40 in Attic it is a bungalow and the basement is completely finish with heating.

Heating main level and basement, basement have cold air return vents and all rooms in main level.

I have a GMVC95 - 0704
Hi-fire output: 67k Btu
Lo-fire output: 47k Btu.

This is a multi-position, two-stage, Variable speed gas furnace.

What do you think is it sized correctly?
Any help, comments would be appreciated.

Live in Winnipeg, lows are -29 in winter



richard

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Old 12-16-2010, 12:26 PM   #2
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Furnace size required for 1100 sq ft house.


I'd think it'd be sufficient. Others may have other opinions.
Don't envy you the cold, though we see our share of the - temps here too.

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Old 12-16-2010, 03:05 PM   #3
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Furnace size required for 1100 sq ft house.


It is the correct size. Next size down is 45,000 Btus and way to small and next size up is 90,000 and too big. I have a 70,000 in a 1360 sq ft with R20 walls and R40 attic and better windows than you.
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Old 12-16-2010, 04:16 PM   #4
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Furnace size required for 1100 sq ft house.


thank for the reply,

I will explain how the furnace comes on.

-current temperature inside: 64deg-F, set furnace to 70deg-F
-Furnace starts on low for a min then cycles on high (like a hurricane blower very powerful) till it reaches 70deg-F this takes about 15min then shuts off for 5~7 min
-Starts back on low for 7 min, shuts of for 5~7min then starts back on low
-This continues through out the entire day is that normal, I would think it would stay on instead of cycling on and off, don't get me wrong it provides enough heat just cycles a lot.
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Old 12-16-2010, 04:24 PM   #5
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Furnace size required for 1100 sq ft house.


What's the FE rating? 90% or higher?

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Old 12-16-2010, 04:36 PM   #6
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Furnace size required for 1100 sq ft house.


it is a 95% HE furnace, goodman, 70k-btu's

I have a GMVC95 - 0704
Hi-fire output: 67k Btu
Lo-fire output: 47k Btu.

I will explain what I mean if a little better about my situation. If the house is 65deg-F and I set the furnace to 70deg-F then the furnace starts on low for a minute then goes to high (like a hurricane blower very powerful) for 15 min then shuts off.

It will start back again in 5~7min to main the 70deg-F but it only lasts for 7 min then shuts off again this continues. I am not sure if this is normal but I would except the furnace to stay on all the time instead of cycling. Don't get me wrong I get enough heat in the house just worried about what effect the cycling is having on the house and furnace.

Thanks for you replies, but I know you all have come across this before just wanted some clarifications.

This is a multi-position, two-stage, Variable speed gas furnace.
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Old 12-16-2010, 05:26 PM   #7
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Furnace size required for 1100 sq ft house.


It is normal for a furnace to cycle while maintaining the set point. To reduce the amount of cycling some thermostats allow adjustment to the hysteresis (allowable amount of deviation between set point on and off) The larger window for deviation the more you will feel the temperature swing.

Another thing to look at is where your thermostat is located, does it truely sense the average temp of the home, or is it in a location effected by cold air drafts.
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Old 12-16-2010, 05:55 PM   #8
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Furnace size required for 1100 sq ft house.


What type of thermoststat / brand and model do you have (post a pic)/ If it is a true 2 stage tstat with a wire on the W2 terminal on the circuit board it will go directly to high fire close to startup as it has dropped more than 1.5 to 2 deg F and the stat will allow high fire. Normally when up to temp it has to drop about 1.5 deg F or 2 to go to high fire. If it is a single stage stat then it uses a timed on 7-10 minute delay on low fire to go to high fire unless Goodman has gone with the algorithym system Carrier uses. I have not seen their new ones as I do mostly Lennox. Sounds like your tstat is faulty anyway. Not sure if you can buy a 2 stage tstat at any big box stores in Wpg and they are more expensive.
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Old 12-17-2010, 10:53 AM   #9
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Furnace size required for 1100 sq ft house.


Thank you for the reply yuri, you seem very knowledgeable about HVAC.

I am going today and check how much cycles I am getting per hour, I will also give check the outside temperature and post the results later on.

In the mean time I have another question I am pondering, if the blower fan is to powerful can it harm the house? How can a house become over pressurized? My blower fan goes on like a hurricane blowing my curtains all over the place, I don't mind the noise except that it is powerful.

Is there a problem with this.
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Old 12-17-2010, 11:05 AM   #10
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Furnace size required for 1100 sq ft house.


The blower should not pressurize the house. That's what the cold air returns are for. Po)
It just makes it a big 'loop' for the air to circulate.

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Old 12-17-2010, 03:46 PM   #11
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Furnace size required for 1100 sq ft house.


It should be setup properly on both stages to get the proper temp rise thru the furnace. Too high or too low IS NOT good and can damage the heat exchangers.
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Old 12-17-2010, 04:18 PM   #12
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Furnace size required for 1100 sq ft house.


Netminder,

"My blower fan goes on like a hurricane blowing my curtains all over the place, I don't mind the noise except that it is powerful."

You either have too many duct taps shut-down (damper closed), branch runs that aren't big enough to allow for slower air velocity or too few branches to distribute the air being moved by the fan.

You can either open dampers, increase the size of the branch runs or add branch runs and lastly you could add vents in the basement or crawl space.
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Old 12-18-2010, 12:05 PM   #13
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Furnace size required for 1100 sq ft house.


Jackofall1, thank you for your comment that solved my problem. The ducts that run to the basement was closed off I opend the dampers on (2) of them and BINGO, blower fan noise vanished, now the system runs good. I guess all the heat vents in the basement was closed off I open (2) in the living room basement, the ones opposite to the cold air return vents, now when the fan goes on it don't sound like a hurricane upstairs and even cycles longer.

thank you all for your help.

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Old 12-18-2010, 12:08 PM   #14
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Furnace size required for 1100 sq ft house.


Yay! We so love happy endings here, thanks for letting us know! Po)

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Old 12-18-2010, 01:21 PM   #15
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Furnace size required for 1100 sq ft house.


Quote:
Originally Posted by netminder View Post
Jackofall1, thank you for your comment that solved my problem. The ducts that run to the basement was closed off I opend the dampers on (2) of them and BINGO, blower fan noise vanished, now the system runs good. I guess all the heat vents in the basement was closed off I open (2) in the living room basement, the ones opposite to the cold air return vents, now when the fan goes on it don't sound like a hurricane upstairs and even cycles longer.

thank you all for your help.

just opening one damper did it ....hhhmmmmm

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