One Pipe steam, Thermostat temp swing recommendations?

rrg

I have a 7 day programmable thermostat for my millivolt and want to know what is the preferred or more efficient settings for the house using steam, when people leave for the day.



I have read to let the house temp drop and warm it back up in the evening. The material I read did not say what type of heating was used in their recommendations.



For evenings should I set the temperature down at night and bring it up in the early AM?



I do like using one temp setting most of the time but can I be more efficient going up and down in temp?



Thanks.

BoBoBoB

setbacks

If you search for old threads, you'll find there's a lot of handwringing over this topic. As far as I can tell, here are the pros and cons:



Pro-setback:

* In an ideal system, saves fuel because the house loses less heat

* Allows cooler sleeping temps, which may be more comfortable

* Long boiler burn times during recovery are more efficient than shorter burn times



Anti-setback:

* Overshoot common, burning more fuel than necessary and impacting comfort

* Long recovery times needed, lowering duration of setback

* Hard to balance system for both maintaining constant temp and recovery--some rooms wind up too hot or too cold after recovery

* Boiler will cycle on pressure, with potential for short cycles

* Boiler will operate at higher pressure, which is less efficient



I would decide this way: if you can use a setback that doesn't result in overshoot, and doesn't require you to crank up the recovery temp to get a comfortable temperature, you're probably going to save fuel. If you get uneven heat, overshoot, or have to crank up the thermostat higher than your normal setpoint to get comfortable, you probably won't save fuel.

Jamie Hall

It's as BoBoBoB says...

If you talk to five people here on the Wall, you'll get at least six opinions...



The amount of setback which is comfortable and which is economical depends on a lot of different factors.



The first of these is the type of heating system.  A forced air heating system -- particularly a high volume one -- will recover to a given level of setback much more quickly than any hydronic or steam system can, simply because it is taking all the air and running it through the furnace.  This is where you see recommendations for large setbacks -- seven or ten degrees or more -- and for setback arrangements where it's cool at night, warm in the morning, cool during the day and warm again at night.  This may or may not be really comfortable; this is also where you see that the "warm" temperature may be around 70 or 72 (F).



Steam or hot water heat responds more slowly.  It may take -- depending on the heating system and the building -- an hour or so to recover from a 4 degree setback.  However, there is a curious side effect: many folks I have heard from say that they are comfortable with the "warm" temperature at 68, rather than say 70 or 72.  There is a reason for this.  There are two parts to being "warm enough"; one is the air temperature which your thermostat reads.  The other, however, is the temperature of the materials of the building -- the walls, the floors, the furniture, whatever.  That temperature will be very close to the average temperature you keep the building at.  It won't change much with the setback.  Thus a steam or hot water system running at, for example, a 64/68 cycle may feel just as comfortable as a forced air system running at a 60/72 setback.  Which is more economical?  One has to experiment to see.  The 64/68 setback arrangement will, however, be much easier on the building and the furnishings than the 60/72 setback will be -- which may be a consideration (in the museum I care for, there are objects which would be seriously damaged by the wider setback, for instance; some of the furniture, the pianos, some of the art work).



If saving energy is your criterion, rather than saving money, even there you may not save much with a wider setback, as the system will have to run for a while to recover, and so long as the temperature of the air is more than the temperature of the structure it will have to run slightly harder to keep the air temperature up -- which may or may not be compensated by having to run slightly less hard during the cool times.



Radiant heating systems are the slowest to respond; with those a good size setback may never recover during the warm time.  They will tend to be much closer to the average of the two temperatures.



So... as I said at the top, talk to five people and you'll get at least six different opinions.

AlexR

I use a setback

I use a 5 degree setback (60/65) on my system; down to 60 at night and during the day on weekdays.  Unless it's very cold for a long time, that means my boiler never runs at night or during the weekday.  I figure I should run the heat when I'm there to appreciate it.



The long boiler-off periods also mean the boiler and pipes cool down to and stay at their base temperature for a long period and I'm only "dumping" two boiler's worth of heat per day.  That is, my basement is unfinished so the heat loss of my boiler and pipes cooling is basically all wasted.  If there were 4 thermostat calls for heat per day, then I'd probably be wasting twice as much energy in the basement unless 2 of them were close enough together that the boiler+pipes were still pretty warm.



When I replaced the 0-30psi gauge on the boiler, I got one that has a temperature reading too.  So it's interesting to see how long it takes the boiler to cool- there's a substantial (212 -> 120) temperate drop over a couple of hours.  So I want my cycles to either be very close together or much farther apart.



 But like the other posts said, some of this will depend on your house (how fast and evenly does it cool), your system, and your preferences.

rrg

Thanks for confirming my suspicions

JamieHall,

The more I thought about it you are right on.

I have heard some neighbors mention that the air heat is quick to heat and quick to cool now that you mention it.



The rooms are more comfortable at 68 with steam. I could never imagine hitting 72 on our steam system. It would feel like a bath house.



60 or 62 sounds like a good number to try for evenings and unoccupied times.

Thank you.