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I have a programmable thermostat to lower the temp in my home at night and during the day when no one is home (both time periods are 8 hours). Is there a point of diminishing returns as far as how much the temp should be lowered during those times? How many degrees?
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No more than four degrees from where it's currently set.
*Miller, you're out of it -- three degrees, tops.If the question is on the order of, "Do I use more gas idling at stop lights than if I shut the car off and then re-started it," then I don't know how anyone could answer that without knowing a lot about your particular situation.In my home, the lowest night-time temperature setting I use in the winter is the one that prevents diminishing returns from my wife.
*Well, in my underinsulated house...I just set it for 60 degrees. I'm here the odd evening only, and overnight normally. The people before me were using 5 chords of wood and 2000$ in gas per season. Last year, 1 chord, and 1200$ was my cost, with this method. If it's going to be a cold night, I light a fire...and normally don't hear the furnace run.Just my humble opinion. I'm no heating expert.L
*The higher temp differential you maintain between inside/outside, the more work it is for the furnace. Imagine trying to keep the house at 100° all winter. Ours shuts down for the night at 11 and, being forced air, brings the house back to 68 or so in 15 minutes the next morning. Poor as the insulation is the temp doesn't really get below 60 with outside temps around freezing. Now that I'm sealing/insulating the house this should only improve. Something slow like hydronic would be altogether different.Does your thermostat log usage? Ours does, for today, yesterday, and total since reset. With this you could figure out the best settings empirically pretty quick.One other observation: your heat plant is probably most efficient working hard, such as bringing the temp up in the morning. In a long cycle, the heat exchanger will reach its working temp just once; with short cycles it will have do it again and again, each type cooling and losing heat up the flue. (This is true of a car too; if restarting it uses neglible gasoline, then yes you will save gas turning it off at lights ... they actually do this in Europe where gas costs $4/gallon. But then will you burn up the starter? Our car gets horrifying mileage during the winter when used for just short hops.)
*Another important consideration is that newer furnaces operate more efficiently when on for longer periods each time. So trying to keep it 68F overnight is going to use more than letting it slide to 63F, where it won't cycle on so often, if at all.We have multiple settings on our programmable t/stat...4 settings over 24 hrs, plus separate weekend and holiday (no one home). Mine is set to go from 70F at 11:00 pm to 63F overnight, back to 70F at 6:00 am. then down to 65F during the day and back to 70F at 5:00pm. It seldom comes on during the night, but brings it up fairly quickly to 70F in the morning. If you happen to be home during the cooler time periods an override button brings it up to 70F.
*Gee Patrick, haven't I heard that somewhere before? ;-)You keep it at a roasting 70°? Wow, I like about 67° now that I've adapted from my California upbringing. Actually, I just looked up to see it's 64° in here and I'm wearing a T-shirt. Pain is all in your mind you know...
*Everything in the house is a heat sink that stores heat for use when the air cools. So, not only are you reheating the air after a cool period, you are also reheating the interior walls and all the contents.Another factor is your climate zone. The colder the climate the less useful it is to set back the thermostat for periods of time. For example as I write this the outside temp is -40C and the interior temp is +22C. With these differentials the cost of bringing the house back up to temp after a cool down is higher than just leaving it up. Plus this is more comfortable. Plus, in the event of a furnace failure the heat sink will provide a longer delay time before pipes freeze thus allowing a better chance of getting the thing fixed before it gets expensive.There is a similiar effect in desert climates with air conditioning. But without the expensive repair challenge.So, I'm not a fan of setback thermostats except in the most moderate climates.
*FredB,I assume your comments to be solely your reasoned opinion, not based upon other authority.I have never before heard of the concept of using your home's structure as a "heat sink" in case of furnace failure at night. This reminds of me of folks awhile back saying they wouldn't have electric windows on their cars 'cause they'd never get out if they drove into a lake -- something we must all apparently do on a regular basis.
*Where ya been bye. .. Fred makes all his own furniture out of ferro concrete, and Gaby parks in the lake on a reglar basis.To each his own. . .ya know???-pm
*Is it plausible to install finned drywall in your house to increase its utility as a heat sink?
*Good grief! I never expected such sarcastic response to a contribution to a person's query for data.While the interior of the heated structure is certainly not the equivalent of a solar house heat sink there is still a lot of mass that needs to be taken into consideration. That it takes significantly longer for a house at interior temp of +22 to reach freezing at cold temps than one at +15 is pretty obvious to everyone who is using their mental facilities. That mass must also be reheated after a cool-down period.How much energy a programmable thermostat saves is dependant on the particular house, climate factors such as temp and wind and heat plant efficiency. Bfore buying or using one a person needs to do some analysis, not just accept arbitrary numbers that may apply in totally different circumstances. Not knowing where the original poster lives I think he needed some foundation to make a decision, not just arbitrary unexplained numbers that may or may not apply to his situation.
*Heat sink or not, the choice is whether to replace lost heat throughout the night or all at once in the morning. I believe the the latter is more efficient because fewer BTU's are lost and furnace efficiency is increased. But if you have -other- reasons not to set back the thermometer, then you may not care about the extra cost. (I doubt the higher temp will buy you more than an extra hour or two, depending on outside temp./wind & house insulation -- this too could be determined empirically.)
*I'd check into replacing the boiler right off. The efficiency of appliances has skyrocketed since the seventies. A new boiler may pay for itself in as little as two years. I'm amazed at the improvements in heating & AC plants esp.Now, is this steam or hot water heat? Ironically, the relatively slow response of the boiler (in heating or cooling off) plus the new insulation may keep the water at a relatively stable temp, so that the setback thermometer doesn't do that much good. Kind of like how turning off your water heater at night wouldn't make much difference.
*BarryYou're a fricken genius man. .. get to a copyright lawdog fast. . . I see serious $$$$ in yer future.No sh*t!-pm
*Patent, not copyright. :)