How do you Set your Programmable Household Thermostat

[wooferhound]

I have just installed a programmable Thermostat for the household Heating and Cooling system. Let me discuss the System in Heating Mode for now so it's less confusing and that is the season right now in Alabama.

The instructions say to set it so that the System is off when you aren't home, and to reduce the temperature when sleeping. I can see that this would have the system running less but seems like it would actually run a Lot more when it fired up again from being off for the last 8 hours while you are at work. The thermal mass of the house needs to be brought up from such a low point that it would run a lot to catch back up.

I had heard of a method of setting the Programmable thermostat so that the system runs the most during the part of the day that the system would be most efficient. In the winter you would set the Temperature to a high point (say 73 F) during a long period in the afternoon when it is warm and the system can heat better. This builds up the thermal mass inside the house when the system is best able to do it. Then have the thermostat gradually reduce the temperature in steps through the evening and morning (to say 70 F) using the thermal mass to help maintain the temperature and the system works less when it is less efficient. Of course in the Summer you would set the Lowest temps in the early morning before daylight, then gradually increase the temps during the day and early evening till you get to the cool down point again in the morning.

So ,  How do you set your Programmable Thermostat ?

[alibro]

Hi Wooferhound

I set my Thermostats to a low temperature when we are at work and in bed and a higher one when at home. Most programmable digital thermostats have 4 temperature settings per day  i.e. morning, daytime, evening  and night. I just set them for 14deg C and 17deg C (we have a coal fire for direct heat) and manually adjust if necessary. Here in Ireland rain is more of a problem than cold so at the times they are set to 14deg C the heat rarely come on. It only takes 30 or 40 minutes for the temperature to reach 17degC. Cooling is not normally an issue so we don't have any aircon.

Cheers

Alibro

[Sly]

Hi Wooferhound,

I get this magazine and there was a good article in the January 2008 issue. Here is the article:  http://www.ebmag.com/images/stories/PDFarchive/2008/01january2008.pdf

If you don't have high speed just go to www.ebmag.com and surf till you find it.

The article included comparaison between a high effiency house and regular house with programmable t-stats and typical settings.

Hope it helps.

sly

[Sly]

Sorry,

I meant evaluation between two R2000 homes (high efficiency) i.e. one with the programmable thermostats and one without.

sly

[FishbonzWV]

Woof,

I've had one for several years now and it took a couple of seasons to fine tune it for comfort. The wife is now "retired" so the daytime temp is not set back like it once was. You will find that you have to follow your circadian rhythm for the most comfortable settings.

I set mine at these four settings:

                       05:00  69F

                       12:00  70F

                       16:00  71F

                       23:00  69F

You'll find that due to the natural body rhythm you will feel cold the closer to bedtime it is. That's why the last setting is 71F at 4PM.  

[DanG]

The only problem I see with setting afternoon temperatures higher is it may be a no-sun day and your system cranks away to reach 'sun warmed' temperature, and the higher temperature will induce a stronger chimney draft effects so proportionately increase leakage and thus cold air infiltration. If the house wants to warm up in winter time think of it as a bonus but don't spend money reinforcing the trend.

Here in Minnesota if we open the south window blinds up to capture as much sun as possible we end up with three warm sunny rooms and five frigid rooms since the thermostat gets fooled and no air circulation occurs with forced air heat. I know it's just this floor plan, but forget to shutter up after the sun goes down there is serious chill climbing in with us.

On the long firing times from setback recovery I agree with you. This year we raised the setback point from 62F to 65F and have seen a probable reduction in overall gas usage, maintaining the 65F overnight means overall shorter run time than the daily hour plus run to bring temperatures up suddenly. For the 30 day period ending mid-January the average temperature was 12 degrees lower, gas used was just 13% more than previous January for additional 40-cents daily cost with $141 gas used, for 42 daily average heating degrees versus 30 prior year. We were very surprised - nothing much else had changed in terms of insulation etc..

Opening the house up and exchanging air with the cool of the morning works good but in the hottest parts of summer twilight is over about 10PM and that is about the time the suns' heat load becomes most apparent - the heat has worked its way through the insulation and roof & walls and must be dealt with then if there is to be any peace in the house - no matter what happened 12-16 hours before. Programming to use power to cool in the mornings may not be needed if it is overcast or rained, the thermostat can't tell that.

[DanG]

Should read: ...if it forecast to be overcast or rainy or cooler than usual later in the day, the thermostat can't tell that...

[Chagrin]

The "thermal mass" concept as pertains to setting your thermostat is a myth. A greater difference between the temperature of your home and the outdoor temperature results in faster heat loss. That's the only rule that applies as pertains to efficiency.

I'd also suspect that a furnace is more efficient when running constantly versus running intermittently.

[SparWeb]

I moved into a new house in 2004.  At the time it was about 10 years old and did not have a programmable thermostat.  I soon corrected that, and have monitored the heating bills ever since.

Assuming the natural gas meter was at zero when it was installed, I use exactly 1/2 as much natural gas as the previous tenants of the house.  We are all away from the house during working/school hours on weekdays, so the thermostat allows the temp to drop.  It also drops overnight, but not during the day on weekends, when we are around.

The issue of thermal mass is a tough nut to crack.  The variation in house temperatures during the day is only 4-5 degrees C (7 to 8 F).  The daily variation in external temperatures, where I live, is about 10-15 C (18-27 F), and in winter it falls in a range far below the house's mean temperature.  At -20C (about 0F) there is a wide gap between the house temperature range and the outside, no matter what time of day it is.

Tweaking the timing of the house's temperature changes according to the sun's schedule, instead of the family's schedule, may lead the "gremlins" to make adjustments of their own.

Unless away on vacation for several days, I wouldn't set the thermostat below 10C, because there are many subtle consequences of reducing the house temperature.  Pipes under the house hover between ambient and house temp, so reducing the house temp too much might allow them to freeze.  Plants, electronics, perhaps other things that don't come to mind right away, might be affected by long periods of cold.

Oh yeah, some houses have humidifying systems.  If the absolute humidity of the house is high, and the temperature drops, then the relative humidity can quickly go to 100%.  If this happens in the winter, ice can form on the insides of the windows.

You say you live in Alabama.  I live in Alberta.  Nothing that I've said is necessarily going to apply to your situation.