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Old 12-11-2009, 04:50 PM   #1
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Is it a bad idea to keep house too cool?


Since there's only a small portion of the time where I actually need a comfortable temp, I tend to keep my furnace at around 12C (even thought of going lower) and have it set to go to around 20 during certain periods such as my lunch and in the morning when I get up. I may also manually override based on my needs. But in general I tend to keep it low, then it just heats up to 20 or so all in one shot if needed. I'm just wondering if extreme inside temp changes like this are bad for the house.

I just do it mostly to save on heat as I don't need the heat on when I'm in bed or when I'm at work. Now that we are getting in the very cold climates without the furnace on the temp drops fairly quick in the house.

Also what is really more cost efficient, keeping it at a fairly steady temp or moving it up only as needed so it runs longer non stop? I'm guessing power cycling on/off costs more as it probably takes a while for the furnace's temp to reach it's full potential so each time it starts it has a period of time where it's not at it's peak. Am I correct in this assumption?

My cat also hates me right about now. Just got home a while ago and it was 11 degrees in the house LOL.

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Old 12-11-2009, 04:59 PM   #2
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Is it a bad idea to keep house too cool?


I also cycle my temperature, leaving it off all night, and only starting the furnace up in the morning. At least I did it that way before I got a wood stove, not I don't use the furnace at all, but temperature cycling never hurt may house, and your cycle of 8 degrees C is not that much.

As for efficiency, you lose heat at a rate proportional to the temperature difference between the outside and the inside of the house. Therefore, the warmer the house, the greater the rate of heat loss. Maintaining a constant temperature of say 68 degrees F will result in a greater heat loss than cycling the temperature down, then up. The amount of energy needed to heat up the furnace is irrelevant to the computation, since you are ultimately going to have to "replace" all the heat that is lost through your house envelope, the more heat you lose, the more it costs.

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Old 12-11-2009, 05:02 PM   #3
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Is it a bad idea to keep house too cool?


I'd be more worried about the cat getting even.

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Old 12-11-2009, 06:23 PM   #4
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Is it a bad idea to keep house too cool?


I'd be worried too. Looks like "Dirty Harry or Harriett" to me. Make my Day
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Old 12-11-2009, 06:30 PM   #5
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Is it a bad idea to keep house too cool?


My last house I heated mostly with wood
Gas cooking, dryer, hot water & heat & my monthly bill was $30-40
I kept it at 50-52 most of the time, never home much
I'd kick the heat on while I started a fire...then the heat was off

Downside is that if the heat fails...and you are not home
The pipes are going to freeze a lot quicker
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Old 12-11-2009, 06:36 PM   #6
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Is it a bad idea to keep house too cool?


You start dropping your temps drastically in Canada and you may get cold and mold spots on your walls. Older homes don't always have good vapor barrier and pink insulation can settle and you will be sorry. If it has a chimney that may also get very cold and could start to freeze up from an extended off cycle. Would never even think of doing what you are doing in Winnipeg.
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Old 12-11-2009, 09:16 PM   #7
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Is it a bad idea to keep house too cool?


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Originally Posted by Daniel Holzman View Post
The amount of energy needed to heat up the furnace is irrelevant to the computation, since you are ultimately going to have to "replace" all the heat that is lost through your house envelope, the more heat you lose, the more it costs.

I'll toss a bit of a wrench into that calculation:

My heatpump will automatically engage "emergency heat" when the temperature differential between the set point on the thermostat and the room temperature is greater than 2F. So if I take the temperature up 2F at a time the emergency heat will not be used, which has to be more efficient.

There is one possible negative to allowing temperature swings -- when temperature drops, R/H increases. Mould requires a pretty high R/H. So if you have a marginal mould problem, it can become a lot worse if you turn off the heat at night. I read about that on the epa.gov.
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Old 12-12-2009, 03:48 AM   #8
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Is it a bad idea to keep house too cool?


Gents it has been established by ASHRAE that a set back in excess of five degrees F will do nothing but burn up the energy you saved in longer recovery time.

If you are using an occupied set point of 68*F you should not set back further than than 63*F. The colder it is out side the more fuel you will use to come back to your 68*F occupied set point.
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Old 12-12-2009, 03:59 AM   #9
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Is it a bad idea to keep house too cool?


There is one possible negative to allowing temperature swings -- when temperature drops, R/H increases. Mould requires a pretty high R/H. So if you have a marginal mould problem, it can become a lot worse if you turn off the heat at night. I read about that on the epa.gov.


You got some thing wrong some how.

The colder it is the less moisture the air can hold and would tend to dissuade the growth of mold.

How ever in a situation where room air heated and humidified meet a very cold surface, say a void in the insulation, the moisture would participate out
as the surface would be at below dew point of the RH.
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Old 12-12-2009, 05:18 AM   #10
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Is it a bad idea to keep house too cool?


Quote:
Originally Posted by hvaclover View Post
There is one possible negative to allowing temperature swings -- when temperature drops, R/H increases. Mould requires a pretty high R/H. So if you have a marginal mould problem, it can become a lot worse if you turn off the heat at night. I read about that on the epa.gov.


You got some thing wrong some how.

The colder it is the less moisture the air can hold and would tend to dissuade the growth of mold.
The amount it can hold becomes less. Which is what makes the RH increase.

EG: A house at 68F(20C) with 35%RH, at 35.6035 grains of moisture per pound of air. Cooled to 54F(12C) with 35.3035 grains of moisture per pound of air will be at 57%RH.


Although I would think it would be more of a problem on a tight house, then a loose house.
I'll bowl to Yuri on it, since he lives in a much colder climate then I do.
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Old 12-12-2009, 07:41 AM   #11
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Is it a bad idea to keep house too cool?


We are selling HRVs to people because the lower and corner areas of walls tend to have poor air circulation because of beds and furniture. Poor airflow=lower temp =sweating like a window. Impossible to boost airflow to the point where that does not happen as lots of people won't run a continuos fan or it is drafty. Older homes have R12 in the walls and if it settles or is improperly installed will have blank or void areas. Homes with electric baseboard heaters are especially bad for cold corners and mold. Ya gotta live here to know what happens and it is all about thermodynamics and airflow and drafts, negative pressures etc. Thats why I am da Top dog in my shop. Plus no one else seems interested, just in it for a cheque $$.

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Old 12-12-2009, 10:38 AM   #12
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Is it a bad idea to keep house too cool?


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Ya gotta live here to know what happens and it is all about thermodynamics and airflow and drafts, negative pressures etc. Thats why I am da Top dog in my shop. Plus no one else seems interested, just in it for a cheque $$.
You got much colder temps there, then I do here.
We don't have that problem as much, since most houses don't have enough humidity. And we ain't at -30F.

Only the homes that try and maintain 40 to 50%RH have that problem in the corners. Around her.
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Old 12-12-2009, 10:48 AM   #13
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Is it a bad idea to keep house too cool?


We/ I try keep my humidity between 35-40% RH. Any higher and the windows sweat. Any lower and you get static and nosebleeds, and dry fizzy hair.
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Old 12-12-2009, 02:59 PM   #14
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Is it a bad idea to keep house too cool?


Posted by Beenthere:The amount it can hold becomes less. Which is what makes the RH increase.




My post was meant too apply to normal home temps.

But, yes if your home is TIGHT and not exchanging enough air per-hour, than of course course the home would retain the moisture and the RH would stay high.

But in the homes that I service the air exchange is more than adequate the air would need HUMIDITY ADDED, not removed as you suggest Been.
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Old 12-12-2009, 03:06 PM   #15
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Is it a bad idea to keep house too cool?


Our house it has just dipped down below 40%
Basement is down to 60%
Our basement stays higher due to high water table
We have a dehumidifier going quite a bit in the summer
Nice to finally have it off in the winter

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