Setback temperature?

ansky

For those of you that use steam, do you set back your thermostat during the day when nobody is home?  If so, how many degrees?  I have been keeping my thermostat at a fairly low constant temperature 24hrs a day.  I have heard that steam systems are not designed for large setbacks.  I figure that if the burner is off most of the day, the water in the boiler will cool to room temperature and a lot of energy will be wasted in the evening when trying to boil that water again and raise the temperature of the room a few degrees.  Or am I wasting just as much energy maintaining a constant temp all day? Opinions?

BobC

Setback

i keep my thermostat at 62 during the day and have a 4 degree setback at night. I don't think a large setback agrees with steam systems.



At this time of year the system comes on at about 7AM and that's it for the day unless it's windy out. I can isolate the upstairs by keeping the hall doors on the first floor closed during the day so any heat from cooking tends to stay downstairs.



When it does get cold it usually comes back on around 3PM and maybe again before the setback at 10PM.



Bob

Jamie Hall

Ah yes...

the great setback debate!  The general consensus -- at least from last year! -- is that anything much over 3 to 5 degrees is actually going to use more oil than it saves.  That was thinking about night setbacks only.  I would think, based on nothing more than thinking at this point, that if you are also running a day setback (so you have night low, morning up, day low, evening up) anything much over 3 degrees is going to be a waste.  You are right, though -- in general steam systems (and gravity hot water, if there any of them left out there!) don't really get along well with setbacks.

Jean-David Beyer

don't really get along well with setbacks.

Radiant heating with slab-at-grade does not get along with setbacks either. For my house, the delay is so great as to make it difficult to program. If I wanted setback at night, I would have to ensure that the heat went off at about noon, and to have it warm by 7AM, I would have to make it start around 10 or 11 PM.



Instead, I set the outdoor reset to match the needs of the house as closely as I can. The system runs about 18 hours a day when it is really cold out. Right now, it runs about 8 hours a day with water in the 80F to 90F range.

jpf321

i don't recommend....

any setbacks .. mine is on constant temp although the thermostat has a built-in, non-configurable 0.5degF SWING. at least that is based on my old 1948 fitzy .. i have no data of any kind yet with my new 2010 slant fin. it could be that the low water mass will change my mind.



it comes down to this, and I think you get it .. how long does the burner run to "recover" from setback vs. how long does it run to maintain temp. there are many variables .. dwelling heat loss and outdoor climate conditions being the main ones. i found that my boiler ran about 20-30% longer to recover than if I had simply left the temp constant.



It turns out that the Energy Star people actually started removing Energy Star approvals on thermostats for a while (perhaps still) .. I'm not sure they even understand the situation .. but i'm not too keen on the thermostats that come out of the box with preprogramed "energy saving" time/temp settings. since I just want it to be constant, but most people use the preprogrammed settings believe that it is saving them money.

ceikey

I've been wondering too...

about setback. I just got a new SlantFin and on a cold start (night time setback to 62 and morning heat to 70) there is steam in the header in 6mins. It seems worth it to me with a new boiler that makes steam quickly. It hasn't been cold enough yet to experience continuous heating to see how fast it makes steam when the water hasn't cooled. I'm guessing a couple minutes max. My house is pretty leaky too so I think the heat would come on 1-2 times at night without a setback this time of year. We'll see how much it runs at night with a setback in January. If it saves me one heating cycle it should be worth it.