Keeping the Gas Bill Down

Kevin Adams

Is it possible to keep the gas bill down by keeping the thermostat set at one temperature 24/7 instead of moving it up and down? Also by using a digital thermostat?

Plumb Bob

No, not really.

Brad White_150

It depends

on what that single 24/7 temperature is... and what your basis is.

Setbacks work best for longer periods but this depends on the mass and insulation of your house. A well insulated high mass house is your best bet regardless of what temperature you set your thermostat to.

Reality says, "That's nice but not what I have to live in".

One rule of thumb I have seen posted here recently (sorry, I forget who did), was to see what temperature your house settled to after two hours of shutting off and to use that as the setback temperature. I suppose it depends how long you would be away and how long the system takes to recover.

The best bet in any case IMHO is outdoor reset with very limited setbacks, say 5 degrees. (OD Reset can, without a "boost" cycle, hobble the recovery time by limiting the available temperature.)

Whether a thermostat is digital or analog matters not. It is still a switch activated by temperature. Digital may be more accurate in theory but not in a way you could feel. So I agree with Mr. Cricket.

Gordy

type of heat

More important what type of emmiters? Slab radiant, suspended tube, underfloor plate, sleeper plate, radiators, base board, forced air?

Agreeing with what Brad has said, I believe if one has a radiant slab. Set it and forget is in order, as compared to a faster responding emmiter. Unless you are out of town for extended periods of time.

Personally I think deep set backs more than 5* are a waste of time. What you think you gain, is lost comming out of set back bringing all the masses in the house back up to temp. Depending on the r value of the structure, and outdoor temps your milage may vary.

Gordy

D107

many outdoor reset controls don't seem to offer a 'boost cycle'

which as you say, hobbles recovery from a setback of more than a few degrees--especially on a design day. The boost cycle that is available is usually used for DHW priority. So perhaps one has a choice of where to boost. But why not both? Considering the relative sophistication of some of the controls out there--intelligent recovery, dhw purging, etc. boost from setback seems an obvious shortcoming. Even our old mechanical 1980 heat timer we had in the city had a morning boost pin. It must be available with Tekmar etc--probably just have to pay for it.

David

Brad White_150

A few comments- similar experience.

My 1986 vintage Centra controller had this, OD reset, 4-way valve, constant circulation with my TRV's on radiators. During AM warm-up or before returning from work, the temperature would boost (using parallel shift of the heating curve) until occupied setpoint was reached. Then it would go back to "maintenence" at a much lower temperature. Common then and I am not sure how prevalent this is today. If not, why not? If so, I must be missing it somewhere.. just me.

One point of clarification/disagreement is that the boost of temperature I see as more of a problem on a mid to warm day when temperatures are depressed with OD reset. At a design day the output would be as warm as the design calls for.

It is an interesting conundrum as to why this would be, particularly if the supply temperature is proportional to the loss being proportional to the OD temperature....A gap in logic maybe?

My thinking as to "why" is that, if a space is setback to say, 60 from 68, it does not matter what the OD temperature is. The degree of indoor temperature rise is the same. A hotter water temperature would take less time to achieve this.

Mike T., Swampeast MO

While I'll generally agree with J. Cricket's answer of "No, not really" there are some possibilities...

If you use a constant setpoint somewhat lower than your current "high" setpoint, you may well find that general comfort is unaffected or even better and fuel consumption might even drop slightly.

The main thing I can say is that if your boiler or furnace does not typically run at least once during the setback period on an "average" mid-winter day, then you are using too much setback and almost certainly are using a higher "high" setpoint than you require for comfort.

D107

e.g. Logamatic R2107

set at outdoor reset default curve: 167 deg supply temp at 14 deg F ; 70 deg day indoor temp and 63 night temp. running with indoor t-stats:

So at 14 deg, night supply temp is, let's say 140. By 2am house temp is at 63, and is kept at 63 until day temp starts at 6am.

Assuming outdoor temp is still 14 deg, supply temp now ramps up to 167 degrees. But that is the supply temp needed to maintain 70 degrees, not boost from 63 to 70. So it will take a long time to get to 70. Maybe til after 7am--not comfortable if you have to be up and about by then. You could set the morning temp to kick in earlier but then you're losing some efficiency. While the pipes may be warm at 6am from the 140 night supply temp, the 7 degree indoor temp rise is still substantial. Therefore the hobbling you spoke of. That's why techs recommend no more than 3 degree setback or setting the Logamatic night setpoint at 2 degrees above the night thermostat to make sure you can maintain at least the 63 degrees in case you figured the curve wrong.

On a 45 degree night, it could conceivably take just as long to get from 63 to 70 degrees inside temp given the supply temp of the daytime curve. I think another thread speaks of the Tekmar TN4 having a morning boost ability.

Aside from the long-standing wall debate on setback savings, it is a matter of comfort. Some people like a 60 degree sleeping temp (air and noses may also seem less dried out at lower temps.) Of course no one likes a 'cold 70' either.

Anyhow just thinking out loud.....

David

Darrell

We played with a computer heatloss program once when we were trying to save money at church by setback stats. At least on the computer...there was no significant savings unless the temp was set back more than 5 degrees for more than 72 hours. 10 degrees setback cost more money to pick up for occupancy than it saved during down time. In the long run adding insulation to the attic was a better way to save gas than setback...but, we went with setback stats anyway! The problem then was a "warm" sanctuary filled with cold pews! So the sensation was of a cold sanctuary and the people complained! We had to bring the heat up soon enough to heat the furnishings as well/

One thing I notice here in Alaska...most residential freeze ups happen during the time that the setback thermostat is allowing the structure to cool resulting in a longer time between heat demands. Put another way: At a setpoint of 70 degrees, the system calls every 45 minutes or so, (just a number out of thin air!). At a lower setpoint of 65 degrees the system call every 55 minutes or so, (probably pretty accurate in comparison to 70 degrees). But, during the time that the structure is cooling, there is no demand for several hours or even most of the night allowing the cold creepies to sneak in and get the piping in the corners!
Bet you wondered why the freeze up calls always happen at 2AM!

ny homeowner

I have 1 pipe steam. I found that setting the thermostat back at night and in the mid day resulted in the house being feeling cold alot of the time. I found that leaving the temp at the same setting 24/7 resulted in more comfort and only a slight 5-10% increase in gas usage. By leaving the thermostat at the same setting, the boiler seems to get "in a groove" and cycles regularly--never running for that long. The radiations get real hot, then gradually get to a warm temperature, then the unit kicks on again.

Mark_46

Here's what Uncle Sam says

Below quote and link are from the DOE's site. Of course its a bit generic and probably doesnt take into account outdoor rest, but you get the idea.

"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. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save".

http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12720

Mike T., Swampeast MO

When that was written for Uncle Sam, condensing/modulating boilers were just a twinkle in some engineers eyes. With condensing/modulating boilers, efficiency does decrease slightly as output increases. ALL manufacturers agree on this fact. Since it takes more energy to increase space temperature than to maintain space temperature, it does take a bit more fuel to recover because the condensing/modulating boiler is "working harder".

Do however notice that this statement from the DOE makes a VERY important observation, "You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed.

The savings from daily setback come ONLY if the lower level temperature is maintained for some period of time! How long does it take for the lower level temp to stabilize?

Good question, but extremely difficult to answer with anything from "a few hours to a couple days"--even in the exact same structure!

David Sutton_6

That says it all

Its all about how comfortable do you feel,
i have a 1998 crysler town and contry lxi all the bells and things you could possibly get with that car, all wheel drive heated seats ( bun warmers ) all of it.
had a problem with the motor, so i put in a new motor, car is great!, if you decide to buy a new car..wait one year then buy it all the money you will save will keep your t-stat at 72*

when i get home i want to be comfortable, not have to wear that stupid sweater my mother-in-law got me for last christmas to be warm in my own home.

so I will change the way i spend my money to FEEL comfortable, t-stat set at 72*all winter
IMHO i'm cold outside and in the custermers house but at home? nope! home is all i have.


David

Mark_46

Good enough for government work : o )

No question! Although it was last updated in Sep 2005, you can be pretty sure ODR and mod/cons where non existant in the US when it was originally published. But the general idea it addresses is still true.

Mike T., Swampeast MO

Generally true? Yes, but from all the research I've done that statement harkens back to a mathematical study of setback in the 1970s and had MUCH to do with poorly insulated and leaky older homes heated by forced air furnaces.

Given two identical looking structures in the same exact climate, the one with better insulation and/or less infiltration will take longer to drop in temperature.

Then, for the same given structure, the warmer the weather the longer it will take to drop in temperature.

With a hot water hydronic system using true constant circulation setback of the supply temperature can at least make space temperature drop in the structure quite consistent regardless of the weather. Again, this is a completely different concept of setback compared to withholding all heat until some lower air temperature is reached.

Uni R_2

Results of a Canadian Study on Setbacks

They said, the deeper the better.

Forced air, modern construction (R2000 spec - tight with an HRV) unfurnished homes were used in the comparison.

I'm still not sold on deep setbacks, but this may be an interesting read for many of you.

Mike T., Swampeast MO

THANKS!

Will have to study further. Do however note that they found no demonstrable setback savings (in this study for these houses) with outside temps above 32F.

Mike T., Swampeast MO

Quite interesting. Both good and bad.

--------------------------------------

Good:

1) Carefully controlled study with two identical homes with one used as control.

2) Different setback strategies and magnitudes used.

3) Solar gain (or lack of such) found to be a HIGHLY contributing factor.

Bad:

1) Forced air.

2) No furnishings and no gains from appliances or human occupancy.

3) Heating systems found to be "50% oversized". YET ANOTHER CONFIRMATION!!!!!!! I can only presume that the furnaces used were sized to best, most efficient conventional practices but found that WHILE MAINTAINING temperature even a "properly" sized furnace was still 50% oversized.

4) CYCLIC space temperature variation close to DAILY temperature variation in a hydronic system with TRVs driven by a DIRECTLY connected condensing/modulating boiler.

David_40

I have kept therm usage records on my home for 18 years and since the rapid increase in NG costs I had to take drastic measures. I have an older home with 70's insulation and single pane windows so a super insulated house may not benefit from my approach. I have two oil filled electric heaters in two bedrooms on timers. Our beds have electric heating pads-very nice and much better than the blankets. I have an electric heater in the kitchen on a timer for warm breakfasts on work days. At night the furnace goes totally off at 9pm and comes back on at 5pm the next day. I'm in NM where the sun always shines so 'winter' here is 40-50H to 20-30L. Once the sun is up winter is no big deal here. In the den for movie nights I have a kerosun heater-love it. Kerosene is expensive but the heater is well worth the cost because my hard to heat den gets up to 80F fast. Well my NG costs are next to nothing now and of course electric is increased but my monthly gas and electric is very moderate. Oh this is old fassioned but I'm glad I have them. Our bathrooms have tripple heat lamps in the ceilings. The house can be 60 degrees but with those on the bathrooms are fine. By the way if my furnace shuts off at 9pm and the house is 68F and the outside temperature drops to 30F my house will be about 60F at 6am. I don't think that is too bad of a drop for an old house. I will probably look into double paned windows this coming spring even though I will never see payback. I think it will help some but will look better and perhaps add value to the house.

Gordy

Rigamero

Sounds like you don't mind going through all the rigamero of turning on, and off different supplemental heating devices. Plus buying kerosene for another. So you are saying that your TOTAL heating bill between electric, kerosene, and NG is cheaper than just letting your furnace maintain even temperature?

What type of Main heating do you have? For me its all about COMFORT. The minimal extra cost, if any of maintaining a comfortable enviroment 72* for us all day, and all night is worth it. I work outside year around the last thing I want to do is come home to my castle, and put a sweater on.

I think the point trying to be made is that with radiant heat you are being more economically efficient buy letting things stay at an eqaullibrium. This is what I have found to be working the best for me.

Gordy

David_40

Well it is simple because my local electric heaters are on timers so I never touch a switch. Timers can handle 15A line limit but all my heaters are set to half that. The kerosene provides a very nice radiant heat aside from warming the air so my wife likes it a lot. We used to crank the main furnace up all the time to try and get her comfortable now with the kerosene she likes it because the den gets to 80F fast. I buy about 10 gallons of kerosene per season nearby so no biggy. The main furnace is gas. I agree with radiant being left on all the time since the lag time is long. Also, I have to stress that NM doesn't really have winter. I grew up in Buffalo area and spent some time in Maine which is real winter.

David_40

Based upon physics heat flow is directly proportional to the temperature difference across the material. The idea of setback is to decrease that difference while asleep or away from the house and reduce the conductive losses. If infiltration is the domininant loss factor in a dwelling then setback probably will not matter. If your house is tight then it will but just dropping the thermostat from 70 to 68 is in the noise. Set the furnace back to 60 at 10pm then if you can stagger the ramp up in the morning such that you don't get back to a setpoint of 68 or 70 until the sun is up on the house and you'll save a lot. Of course if your in Alaska forget about the sun coming up.

Carll

Continually running furnace almost!

Is it possible for a house to be so drafty, built in 1909 2 floors plus basement for the furnace fan to continuously run and for the 6 gas jets to only kick off for less than a minute before they are kicking back on again? Filter is new and I tried adjusting the gas pressure, what am Ilooking for there also in that adjustment? Please help!