Fasten your seat belts...

Jamie Hall

I just read that the DOE has put out a recommendation for people to use 7 to 10 degree (F) setbacks when they are not in their houses. Better begin thinking about what you are going to say…

LRCCBJ

Nothing wrong with a 7-10F setback IF you have the capability to recover in a reasonable amount of time. Most of the time, FHW radiation will NOT allow a reasonable amount of time. Of course, you can use a programmable 'stat to achieve a setback in an unreasonable amount of time, however, that unreasonable amount of time is not fixed. You might need 4 hours to recover when the ambient is 30F. You might need 10 hours to recover when the ambient is 0F.

Additionally, with a mod-con, this approach is directly contrary to fuel efficiency and savings. At the end of the day, you're probably even on cost when the modcon must recover at 84% efficiency rather than greater than 90% if there is no setback.

This large setback approach is generally quite frustrating for most homeowners with FHW to understand and implement.

I will state that I can do a 10F setback on a FHA system and deliver 70K to the space. The recovery is less than two hours. One of the benefits of FHA. I might suggest that the DOE was thinking of FHA systems with they suggested such an approach.

It is also likely that steam systems can typically recover 10F in two hours, under most conditions, due to the elevated supply temperatures and the generally oversized radiation that is typical in steam systems.

So, YMMV and it is strictly dependent on the capability of the radiation.

ethicalpaul

Do you have a link to this? I assume people will react the same way they did when Carter suggested people put on a sweater.

ChrisJ

I can easily do a 10f setback without issue.

I won't but I can.

SlamDunk

If energy prices spike, people would do that without being told to.

EBEBRATT-Ed

The set back you can do depends on the OA temp as well. IMHO 7degrees is a bit much at design conditions. 4-5 is probably OK.

But a set back in some buildings with some heating system will not save any money. You have to re heat the walls, floors, ceilings furniture etc etc. Not much savings and may cost you more.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1819361#Comment_1819361

Reheating doesn't make sense. Yes you need to bring the mass back up to temp but that heat is never lost, you get it all back when the room cools. The objects simply store it.

The cooler the space the less heat loss. A manual j shows this. If the system isn't broke I don't think it's possible to cost more to do a setback.

GGross

https://forum.heatinghelp.com/discussion/comment/1819233#Comment_1819233

It's pretty thorough as far as recommendations go. They even mention heat pump users, and those in severe climates are poor candidates for setbacks. The steam and radiant floor advice was not my favorite lol

https://www.energy.gov/energysaver/programmable-thermostats#:~:text=You%20can%20save%20as%20much,those%20in%20more%20severe%20climates.

ethicalpaul

Thanks for the link, @GGross! That struck me as a well-written, useful guide. Where's the bad part, Jamie?

What was the part about steam and radiant floors that you didn't like, @GGross ? It seemed reasonable to me

ethicalpaul

https://forum.heatinghelp.com/discussion/comment/1819246#Comment_1819246

Reduction of waste is good even if energy prices don't spike.

GGross

https://forum.heatinghelp.com/discussion/comment/1819421#Comment_1819421

Reasonable for sure I just don't like how vague this was.

"However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time."

It sort of feels like its added in there with a little less weight, followed up by suggesting a programmable thermostat and using guesswork. I think the radiant floor setback discussion specifically could be a whole report for itself, it may be more helpful for the average homeowner. But then again they will end up here if the guesswork gives them trouble lol. Who am I kidding, nobody is really going to read this, just some headline on facebook or the like.

Sal Santamaura

Interesting comments, but I expect the entire thread will be irrelevant two and a half months from now.

Revenant

Sal, I get what you are saying. However there are a growing group of people who on their own volition will try to reduce their energy usage and carbon emissions.

So if the DOE wep page goes away in the future, here it is:

You can save money on your heating and cooling bills by simply resetting your thermostat when you are asleep or away from home. You can do this automatically without sacrificing comfort by installing an automatic setback or programmable thermostat.

Using a programmable thermostat, you can adjust the times you turn on the heating or air-conditioning according to a pre-set schedule. Programmable thermostats can store and repeat multiple daily settings (six or more temperature settings a day) that you can manually override without affecting the rest of the daily or weekly program.

Thermostat Operation

You can save as much as 10% a year on heating and cooling by simply turning your thermostat back 7°-10°F for 8 hours a day from its normal setting. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates. 

The smaller the difference between the indoor and outdoor temperatures, the lower your overall cooling bill will be.  You can easily save energy in the winter by setting the thermostat to around 68°F to 70°F while you're awake and setting it lower while you're asleep or away from home. 

In the summer, you can follow the same strategy with central air conditioning by keeping your house warmer than normal when you are away, and setting the thermostat to a setting as high as is comfortable for you when you are at home and need cooling and to ensure humidity control if needed.

Although thermostats can be adjusted manually, programmable thermostats will avoid any discomfort by returning temperatures to normal before you wake or return home.

Avoid setting your thermostat at a colder setting than normal when you turn on your air conditioner. It will not cool your home any faster and could result in excessive cooling and, therefore, unnecessary expense. 

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. In fact, as soon as your house drops below its normal temperature, it will lose energy to the surrounding environment more slowly.

During winter, the lower the interior temperature, the slower the heat loss. So the longer your house remains at the lower temperature, the more energy you save, because your house has lost less energy than it would have at the higher temperature. 

The same concept applies to raising your thermostat setting in the summer -- a higher interior temperature will slow the flow of heat into your house, saving energy on air conditioning. Check out our home heating infographic to learn more about how heating systems and thermostats interact.

Limitations for Homes with Heat Pumps, Electric Resistance Heating, Steam Heat, and Radiant Floor Heating

Programmable thermostats are generally not recommended for heat pumps. In its cooling mode, a heat pump operates like an air conditioner, so turning up the thermostat (either manually or with a programmable thermostat) will save energy and money. But when a heat pump is in its heating mode, setting back its thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed programmable thermostats for heat pumps, which make setting back the thermostat cost-effective. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems.

Electric resistance systems, such as electric baseboard heating, require thermostats capable of directly controlling 120-volt or 240-volt circuits. Only a few companies manufacture line-voltage programmable thermostats.

The slow response time -- up to several hours -- of steam heating and radiant floor heating systems leads some people to suggest that setback is inappropriate for these systems. However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time.

Alternately, a normal programmable thermostat can be set to begin its cool down well before you leave or go to bed and return to its regular temperature two or three hours before you wake up or return home. This may require some guesswork at first, but with a little trial and error you can still save energy while maintaining a comfortable home.

Choosing and Programming a Programmable Thermostat

Most programmable thermostats are either digital, electromechanical, or some mixture of the two. Digital thermostats offer the most features in terms of multiple setback settings, overrides, and adjustments for daylight savings time, but may be difficult for some people to program. Electromechanical systems often involve pegs or sliding bars and are relatively simple to program.

When programming your thermostat, consider when you normally go to sleep and wake up. If you prefer to sleep at a cooler temperature during the winter, you might want to start the temperature setback a bit ahead of the time you actually go to bed. Also consider the schedules of everyone in the household. If there is a time during the day when the house is unoccupied for four hours or more, it makes sense to adjust the temperature during those periods.

Other Considerations

The location of your thermostat can affect its performance and efficiency. Read the manufacturer's installation instructions to prevent "ghost readings" or unnecessary furnace or air conditioner cycling. To operate properly, a thermostat must be on an interior wall away from direct sunlight, drafts, doorways, skylights, and windows. It should be located where natural room air currents–warm air rising, cool air sinking–occur. Furniture will block natural air movement, so do not place pieces in front of or below your thermostat. Also make sure your thermostat is conveniently located for programming.