Greetings to all from a long time lurker and 1st time poster.
I own a brick Chicago Bungalow, built about 1920 with gas fired hot water heat and cast iron radiators. I get all kinds of different opinions on whether to use a ‘set back’ thermostat to lower the heat when we are away. Some claim it is a good idea, others say that hot water boiler is most efficient when the temp is kept constant.
Any thoughts?
Thanx much for your opinions.
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Replies
Your boiler will not operate any more or less efficiently if you use a setback thermostat. The combustion efficiency is not going to change significantly in properly operating boiler.
The concern with a non-condensing boiler is that the set back is too great and allows the system to cool down to the point that regular condensing is occuring in the cast iron sections. This may or may not be a concern with your boiler/piping arrangement/controls.
If the inside air temperature is lower, for a given outside air temperature, the heat loss is less and the fuel required to heat the house is less, all other factors being the same. Within the limits of the capacity of your boiler to "catch up" and the consistencey of your schedule, etc., set back thermostats will save you some energy, in most cases. A lot of factors come into play as to whether or not the savings will be significant.
You may or may not like setback. I personally like the house cooler at night. You will also have to learn the reaction of your house. If you like it at 70 and set back to 62, how long does it take to get back to 70?
A setback thermostat is not an overly expensive item, and if you decide that you do not like it, they also operate in a "set it and forget it" mode.
The better Honeywell's, and I think some others, have adaptive controls so that they ramp it up so that the it will reach the new programed tempature at the set time.
Growing-up in Chicago, we had hot water heat controlled by a "bagel" Honeywell thermostat. It was quite simple to turn it down, a tad, at night; but bumping-it-up in the mornings was a different story.
When we moved to Texas, the house had nearly the same thermostat, but it controlled the central AC and forced air heat. Within a week or two, I bought the Sears entry level set-back thermostat for heat/AC for something like $30.00. It worked well for 18 years. About 10 or so years ago, we replaced the worn furnace and upgraded the AC. I must have been in quite a good mood, as I sprung for the Top-of-the-line Honeywell ChronothermIII thermostat for an additional $130.00.
Like adding insulation to the house, this is an expenditure that actually has a payback to it. The thermostat has four "periods" to be set. Wake, leave, return and sleep. These are set for the five weekdays, and once again for the weekends. If at any time the scheduled setting is uncomfortable, there is also a facility to temporarilly override it.
The thermostat does need two or three days to acclimate to a new seting, then it has the capability to "sense" when it should come-on to reach the set temp at the time you have chosen. Of course, this ability works both with cooling and heating.
I do not know if these are compatible with hot water systems, but if they are, or a different model is, I highly recommend them. As long as you don't go overboard on the "set-back" the system can attain the desired setting within a reasonable economical time. I have definitely seen an energy $aving$ by only a 5 or 6 degree offset.Arlington, Texas (The dash in Dallas-Fort Worth)
Practice...'till you can do it right the first time.
There are few valid generalizations, but one is that a set-back will ALWAYS save you $$$, for the reasons listed in prev. posts. Own house has set-back on heating and HW heater.
A setback thermostat will always save you money if you use it. There is less heat loss from a house in winter if the inside temperature is cooler. The more hours per day you are cooler the more you will save.
I recommend a 7 day thermostat so you can set it to not drop the daytime temperature on weekends.
Be very careful which thermostat you choose. Many setback thermostats run on battery power, and if the battery dies you loose all heat. A stupid but common design among setback thermostats. Many also loose the program when you change the battery, so you have to reprogram the thermostat often. None of these shortcomings are advertised on the package, so you have to read the instructions carefully and return the thermostat to the store if the instructions reveal these deficiencies.
Carrier is one brand of thermostat that doesn't have these problems. It uses no battery, it will retain the program for a week with no power, and even if you go beyond a week without electricity and the program is lost it defaults to a constant setting of 70° so as soon as electricity to the building is restored you get heat. When you pull the wiring for it, it requires an additional conductor in the bundle than standard thermostats.
"A setback thermostat will always save you money if you use it. "Not ALWAYS.It does require that the thermo time constant be significantly less than period of the setbacks.HOmes with high mass construction or high mass radiant systems won't becuae the house might be hours or even days behind the thermostat.
HOmes with high mass construction or high mass radiant systems won't becuae the house might be hours or even days behind the thermostat.
You mean that our house, which normally only changes 2º (sometimes less) in a 24 hr period, wouldn't benefit? Not that we have a thermostat now...
They control active heating or cooling systems, right? <G>PAHS Designer/Builder- Bury it!
I was thinking the same. Here in Miane on radio WVOM, in bangor, they have a saturday HO advice show. one of the main players is an old energy professor who is always up on the studies and doing experiments on his own houses.he claims that there are several objective studies that edemonstrate that in a well insulated house, setback thermostats don't save any moneyI have no direct experience myself, but his reasonnning seems logical to me - that the energy saved during the night is used up to regain normal temp in eraly AM.Now if you are gone all week, and do setback for the five weekdays, and warm up on the weekend, that would be another story, as would an older house with lower quality insulation that loses more heat at night.
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"I have no direct experience myself, but his reasonnning seems logical to me - that the energy saved during the night is used up to regain normal temp in eraly AM."No is a "normal" lossy house and the thermostat set backs are set correctly.The idea is that that the thermostat will lower the setpoint BEFORE the time that you want it to cool off so that the stored energy is used to keep the house semi-warm. And likewise the set it up so that it reachs setpoint when you want it to be warm.So the stored energy that you got out of the house and one end put back at the other.However, the head losses are propertional to the difference in temps between the inside and outside. So during the time period where temp is lower then there are less losses and the furnace runs less.
"...that in a well insulated house, setback thermostats don't save any money."
I have performed some informal information gathering with my own home and system over the years. What I have found out confirms that statement, under some conditions. I have a two-stage furnace so the "usage numbers" aren't exact. (By that I mean that I can only track when the thermostat call for heat, not how much is on the 1st stage oe the 2nd stage).
I have found that in mild heating conditions (for me that is with low temps above 10 degF) that with a semi-well insulated house (walls at R-25, roof is R-50) the setback thermostat on a gas FA system, the run times are slightly less than set a steady temp , if the the setback was 5 degrees or less.
When the setback was greater than 5 degrees, in mild conditions, runtime about the same as no setback.
In temperatures below 10 and nearing my design conditions of -10, setback would result in longer runtimes. Take into consideration that my system is marginally sized, intentionally, but at 10 below, my furnace cannot maintain 70 degrees in the house. Through in the setback on 15 below day and it cannot catch back up. So in very cold conditions, I maintain at a steady temperature.
Only 'not always' that could be is if the house is so well insulated and the thermostat so expensive that the interest lost on the thermostat cost is more than the small set-back savings. Is that what you mean? Overall BTU loss for heating is lower in all set-back cases, may be small, but is there - would love to see a thermodynamic model in Maxwell 3D or other FEA program that says otherwise.
"Only 'not always' that could be is if the house is so well insulated "That brings up 2 points.First while I said it will have little affect if the house has a large thermo mass a more acurate statement would be if it has a large thermo time constant. Which can be had with either a large thermo mass or a large thermo resistance.But as you mentioned if the basic losses are very low to start with whatever you save might not even cover the cost of the batteries.
"I recommend a 7 day thermostat so you can set it to not drop the daytime temperature on weekends."
The basic programmable t-stat is called "5 + 2" where there is a weekday program and a weekend program. Don't confuse this with a real "7 day" program, where each day of the week is prgrammed individually. This is unnecessary for most residences and waste of money.
A better way to save money is to control the water temps based on the outside air temps. Also known as outdoor reset. For every 3 degrees you drop the water temp, you save 1%. tekmarcontrols.com has lots of info and the best controls in the industry.