Maintain temperature or turn off completely

TeachMeSteam

What is the most efficient? Turning off your boiler when you leave for work or keeping it on at a low temperature and having the programmable thermostat turn it on an hour before coming back from work?



I am getting conflicting opinions on this from google but most seem to favor turning it off. And, intuitively, it would seem that there can be no reason that keeping the equipment on would be the better idea.



But, recently, an HVAC talked to me with respect to an A/C system. He told me that it's better to keep the A/C on at a low temperature and then turn it up when you need it. He was very adamant that when it's a very hot day, the condenser will overwork to get it back from such a high temperature all at once and burn so much energy. He was so sure that you save more energy by maintaining a low temperature.



I am assuming that this question applies similarly to boilers and A/C units. What is the correct answer, should I turn off or keep it on?

icesailor

Maintaining the difference:

There will be conflicting opinions.

On many occasions, I have sat in my chair in the living room for the day when it is cold out. Like a few times in the teens. My set back thermostats have a high of 68 and a set back of 58. They turn off at 8:00 am in the morning and come back on at 4:30 PM. There is a big digital indoor/outdoor thermometer on the table in view. I have a sweat shirt on and warm clothes because I have been outside early. The clock trips. The burner never starts for the entire time. At 4:30PM when the clock jumps up, the burner starts. The temperature in the room is still above 60 degrees. Regardless if I had shut off the switch, in my case, the boiler/burner would not have run.

My home is a 10 year old Cape on Cape Cod.

When I leave home in the AM, I switch the thermostats off or down to their set back setting. It's always warm when I come home. I'd rather be warm. I'll spend the pennies.

TeachMeSteam

I'm thinking setback is better

I found this link which suggests that turning off the boiler or putting it to a setback is best:



http://www.energy.ca.gov/releases/1999_releases/features/1999-feature-08.html

Gordy

Setback Savings

The savings from setback assumptions are all over the place. Way to many variables to consider type of heating, weather, condition of the envelope, length of time in setback. Bottom line if it makes you think your saving money then by all means go ahead.



 Personally I think its not that much if your home envelope, and heating system is efficient. If you set back 10* for 8 hours, and your house actually cools down that much I would say the envelope needs tightening up a bit.



 When your house cools all that mass needs to be heated back up which will take more energy than maintaining the same temp. That cooled mass will lag in getting reheated also which will result in lack of comfort. Furniture, walls etc will give off a chilling effect. ( the cold 70 we call it).



 I can see a benifit if going on vacation of course.



IF I could save 10 % a season that would be 50 bucks.



Gordy

Gordy

interesting

This graph actually shows that the rate of supposed saving goes down as outside air temps go down.



Gordy

nicholas bonham-carter

off or on?

if you had an hour-meter for the burner on time, and another for the thermostat call for heat time, then you could leave the thermostat set for the higher temperature, and turn the boiler off in the morning. when returning, i think you could compare the run-time of the boiler [after you return, and it is recovering] and the thermostat while the system was off] to see what the difference was.

true economy of course is a result of pipe insulation, good venting, and low pressure.--nbc

Jean-David Beyer

Setback savings.

I agree with someone earlier in this thread who remarked that there were so many variables in this issue that we cannot come up with a one answer fits all response.



I have outdoor reset on my hot water boiler (mod-con boiler) and heat my house mainly in my downstairs zone that is radiant heat in a slab at grade. I do not know if the slab is insulated or not. My walls are solid urea-formaldehyde foam, the ceilings are a lot of fiberglass. My windows are Marvin thermopane type with argon gas between the panes and optically coated.



My reset curves are set very carefully so that on cold days, the heat tends to run "all the time"; I have had it run for 18 hours non-stop according to my thermostat that keeps track of how many hours it calls for heat. Of course, the thermostat has no idea how often the boiler runs.



Back when I did not know what I was doing, I tried using setback with that slab. I started turning the heat down at about 10 PM and back on at 6AM. Well the temperature would go down a few degrees overnight on very cold nights, and it would take most of the day to get the slab hot again. To get it to cool down in the late evening, I had to have it set back about noon, and turn the heat back on about 10 PM to get it warm again by the time I woke up. When I understood what was going on, I abandonned setback in the radiant heat slab zone.



I do use 4F setback in my other zone that is heated by fin-tube baseboard. But the reset there is pretty extreme as well, so it takes several hours to recover from the overnight setback. The boiler controls for that zone are such that it follows the reset curve for 2 hours and if it has not recovered, it raises the supply temperature by 10F in an attempt to recover faster. I just enabled that feature last week, and it has not gotten really cold out yet. It appears to be effective, though.

Gordy

heating system type

    It sounds as though the OP has steam, or Baseboard/ Radiator heat. As I said before type of heating system plays a role. Rads, Baseboard, Scorched Air all have low mass emitters. Cast iron rads have a medium amount of mass. But the mass of the home still plays that cold 70 role, even if emitters are quick to dump heat into the home.





Gordy

John Mills_5

Overheating?

I grew up in a house with a converted gravity system. We only dropped a couple of degrees at night. If the radiators got cold, it took forever to get all that water hot, then the radiators, then the air. Then by the time the radiators were cooking and the thermostat satisfied, the house would keep warming well above setpoint. So seems to me, with steam or large old radiators, leaving the stat alone would be the wisest move. If you have baseboard that warms quickly and plenty of it and are running 180° water. probably could warm the house fairly quickly.



Remember with any setback, heat or cool, you are having to condition everything, not just the air. Furniture, drapes, carpet, everything gets cold and as the air heats up, heat from the air gets used to heat all of the surfaces & objects in the house. Same with summer, stuff warms up, humidity rises, a minimal setback in hot weather is about all you can do.

Jean-David Beyer

Furniture, drapes, carpet, everything ...

Yeah! If you have some musical instruments, such as real pianos, harpsichords, and the like, they absolutely hate temperature changes. They do not much like relative humidity changes either. Not only do they go out of tune, but sound boards can check (expensive to replace), felt on the hammers deteriorate or come unglued, and so on. I do not know if they prefer any particular temperature, but they do not like changes.

nicholas bonham-carter

Fuel use during recovery fro setback

I have been thinking about setback benefits/drawbacks, since all the hype for the nest thermostat hit the news.

I think the key is to know how much fuel will be used for a recovery from setback. This easier for a gas system than oil.

So, when you setback the thermostat , note the gas meter reading, and after a few hours at the lower temperature, note it again and set up the temp to the normal point. As soon as the temperature has recovered, then once again take the meter reading.

Somehow these readings can be compared to show you if there is any saving for short periods of setback. Obviously, a vacation setback is going to be more beneficial.

I don't know whether this will guarantee programmable thermostats re-entry into the energy-star hall of fame.--nbc

Jamie Hall

Sort of the perpetual debate...

And one which, I think, pretty well has to be answered on an individual basis, by experimentation.



In the main building which I superintend, the setback is only 3 degrees -- steam.  That seems to work well.



I would add to some of the above comments, though, that in some cases there are considerations other than pure comfort or energy use.  These have to do with the impact of varying temperatures on the building itself, or on things in the building (keep in mind that I am in the museum business here!).  We have found that daily temperature swings of more than a few degrees are very hard indeed on older furniture (and in fact can be catastrophic) and on musical instruments (for example, to pay only for keeping the pianos in tune with more of a setback I would have to save at least 10% on my heating bill -- no hope).  Oil paintings are less affected, but can be damaged.  So can genuine plaster (not plaster board or sheetrock, but those don't last anyway).  These various oddments don't really mind slow, seasonal changes such as might be seen in an unheated house; it's the daily up down up down up down which causes problems.

nicholas bonham-carter

setback or not?

i agree jamie, and i use no setback; but i am looking for a procedure for others to follow, if they wish to see with their own eyes what works, and what does not save fuel.--nbc