To Run furnace at 72 degrees all night or not

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Old 12-16-16, 02:36 PM
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Question To Run furnace at 72 degrees all night or not

Coldest day yet 20 - 30 degrees with added wind-chill. House temp set to 64 at bed time and read 64 at 6am. It took until 3pm to reach 72. Now this may or may not indicate other problems with my furnace, however, "She who must be obeyed" asked me if it would be better to just keep the temp at 72 when Very cold instead of lowering the heat to 64 since it takes so long to raise the temp. What do you think.
 
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Old 12-16-16, 02:43 PM
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8 degrees is a bit of a large setback. I wouldn't do any more then 4-5.
Depending on how the furnace was sized, that may be getting close to design conditions.
 
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Old 12-16-16, 02:51 PM
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I'd be more inclined to be looking at doors and windows, for air leaks or old single pained windows, not enough insulation, in walls, ceiling and under the floors.
https://www.energystar.gov/index.cfm...sulation_table
 
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Old 12-16-16, 03:23 PM
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You nailed that. Old house and I need to put in new windows etc...
 
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Old 12-16-16, 03:54 PM
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Not necessarily.

Setting back the thermostat by 8f is okay. Two to three hours to recover is okay, 8+ is not.

Setting back does save energy.

If you have a gas or oil furnace it shouldn't take all day to recover unless there's a problem. Heatpumps and electric furnaces are a different story.


Furnaces have a heck of a lot of capacity and shouldn't struggle to keep up like heatpumps and ac units.

Many problems can go un-noticed including low airflow causing the limit to cycle the burners off during a call for heat.

Furnace can be under-fired, other issues can cause it not to keep up.

What's the brand, model number and capacity of this system?

You'll have to open access panels to get this info.

Furnaces and air handlers have name-plates with the info.

You could blow thousands on new windows and not fix the problem. Changing windows and doors is often the most costly way to reduce heat loss. If you already have double pane windows, low e windows will save 10% if you're lucky. Heat loss through windows may not be more than 30% of heat loss and that's with really crappy windows.
 
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Old 12-16-16, 04:03 PM
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8 is a reasonable setback if you can recover from it quickly. At the moment, I agree leaving it at 72 is probably a good idea if you are in the house while it's trying to warm back up. Once you resolve the reason this is taking so long, I would not hesitate to set it back again to your preference.
 
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Old 12-16-16, 05:03 PM
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An inexpensive programmable thermostat would give you the ability to set it back and automatically move it up several hours earlier. You could also use 70 or 68 instead of 64 while you are working on the insulation.

Insulation and other even easier improvements are frequently discussed right here, just ask.

Bud
 
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Old 12-19-16, 07:27 AM
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What's the brand, model number and capacity of this system?
Sorry about that I should know better Muggie.
Carrier Weathermaker 9200 Model # 58MXA060-12112

If I have it right (at least part of it) the most likely culprit is somewhere in airflow. Whether intake or Exhaust. This seems to coincide with another problem I have been having. I will post more info later today as I get it.
 
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Old 12-19-16, 08:16 AM
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I'm not sure on the capacity. I will look it up and post it later.
 
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Old 12-19-16, 02:36 PM
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Sorry about that I should know better Muggie.
Carrier Weathermaker 9200 Model # 58MXA060-12112

If I have it right (at least part of it) the most likely culprit is somewhere in airflow. Whether intake or Exhaust. This seems to coincide with another problem I have been having. I will post more info later today as I get it.
oh, ignore the stupid screen name, i've had this account for a long time and have tried to get it changed. no luck.

Anyhow, it appears to be a 60 000 btu gas furnace.

There are a few things to check...

1. When you turn the stat up, make sure the burners run continuously and don't shut off while the fan stays on. Monitor the furnace for half an hour of continuous operation -> you can listen or take off the top cover to see the burners.

Burners cutting out is most likely overheating - safety switch shuts them down. in that case you need to look at airflow issues. could also be overfired.

2. If that's fine, you need to see if the furnace is underfired. Turn off all appliances and clock the gas meter.

Follow the instructions here -> How to Clock a Gas Meter — HVAC Tech Hangout

If the furnace is burning the right number of BTUs per hour and running continuously, the issue is with the duct system (major leakage/disconected runs - especially if u have attic or crawlspace ductwork) or the house, or the furnace being undersized.

undersized furnace is exceedingly unlikely.

If underfired, you need to call a technician to check and adjust the gas pressure.
 
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Old 12-19-16, 04:22 PM
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oh, ignore the stupid screen name, i've had this account for a long time and have tried to get it changed. no luck.
Is that why you are hitting your head, or is it just the computer? Been there done that.
 
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Old 12-19-16, 07:25 PM
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neither. but with frustrations over the crap going on in the world and worry about the future, maybe it's a good representation.

or maybe i need a change of avatar/profile picture as well.
 
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Old 12-21-16, 04:08 AM
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I have a new blower motor coming. I will go over the system once it is in. Hopefully that had some thing to do with this issue.
 
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Old 12-21-16, 04:14 AM
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My furnace took 5 hours to bring up temp from 65 to 72. I suppose that is good?. I set my t-stat to a 1 degree swing, and it fires 12-13 minutes on, and then 11-12 off. My stat keeps track of "furnace time" and it consistently comes out to around 50% of the time running. This is keeping steady 72 around the clock. I have tried the other way with a setback at night and what happens is that 50% number goes up.
 
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Old 12-21-16, 08:33 AM
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How much does the percentage go up? One or two percent versus 20 or 30 would be a big difference.

FWIW, I have a part time house of about 2,000 square feet which I turn down 14 when I'm not there. I have yet to see it need more than an hour to make up that difference (we were at -23 F at one point this past weekend, so it has been cold outside when I'm doing this).
 
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Old 12-21-16, 01:08 PM
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My furnace took 5 hours to bring up temp from 65 to 72. I suppose that is good?. I set my t-stat to a 1 degree swing, and it fires 12-13 minutes on, and then 11-12 off. My stat keeps track of "furnace time" and it consistently comes out to around 50% of the time running. This is keeping steady 72 around the clock. I have tried the other way with a setback at night and what happens is that 50% number goes up.
Every house is going to be different.

it's going to depend on how the furnace was sized relative to heat loss.

Most furnaces are oversized, it's possible that yours was sized much closer to design heat loss.

Having long cycles is a good thing, provided that they can't be attributed to a problem with the furnace, duct system, or excessive heat loss.

I recommend that you do the tests I posted before to make sure that the furnace is running at rated capacity.

If it is, you can move on to the duct system and house.
 
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Old 12-23-16, 09:47 AM
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A few percent. More than 5, less than 15.....

That is a very small sample size, though.
 
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Old 12-23-16, 12:12 PM
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Received and installed new motor, $80 w/shipping and a Cap. Installed like a dream. It may have taken care of my slow heat rise issue or not. For now I have heat and will monitor things for the next few days.

Merry Christmas
 
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