Home>Discussions>INSULATION & HVAC>to "turn" or not to "turn" down thermostat to save $$$
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Lin
to "turn" or not to "turn" down thermostat to save $$$

Was recently listening to one of the a.m. news networks, and they gave some tips to help homeowners to save on energy costs.

http://www.cbsnews.com/stories/2011/01/10/earlyshow/living/home/main7230719.shtml

One was:
"For each degree they lower the temperature (from a default of 70 degrees) over an eight-hour period, consumers can expect to cut their bills by one percent to two percent, according to Energy Star at the Environmental Protection Agency."

Makes sense and its what many of us have been told over the years - and why programmable tstats are so popular:confused:.

But its contrary to what I've been told recently re: my Buderus boiler - I was turning down the tstat during day, and turning it back up in evening, but was told this practice actually "confuses" the logamatic computer that governs the boiler. Have been told to set the tstat and leave it alone. "That" will save on energy costs.

HoustonRemodeler
Re: to "turn" or not to "turn" down thermostat to save $$$

If you elect to lower and raise your thermostat to save on costs, do not make the difference in change more than 7 degrees. After 7 degree differential, a heating or cooling system generally becomes less efficient in overcoming the temperature spread than leaving it set at one temperature all the time. This 7 degree spread has been known for 30 years.

hvhehcca
Don't Turn it Down

If the boiler is utilizing the Logomatic/Ecomatic Control and a Buderus Thermostat. Your contractor is correct it will confuse the boiler.

That therm is learning the heating cycle of the room/area and providing feedback to the boiler control. The boiler takes this into consideration in it's water temp calculation in conjunction with the outdoor reset. Allowing the boiler to send the correct water temp out to the system to overcome the heat loss for that particular day.

LeonardHomes
Re: to "turn" or not to "turn" down thermostat to save $$$
HoustonRemodeler wrote:

If you elect to lower and raise your thermostat to save on costs, do not make the difference in change more than 7 degrees. After 7 degree differential, a heating or cooling system generally becomes less efficient in overcoming the temperature spread than leaving it set at one temperature all the time. This 7 degree spread has been known for 30 years.

I would disagree when refering to setting back the temperature in general terms.
I don't know where you get the 7 degree figure.

-- Any amount of temperature set-back (either done manually or through a programmable thermostat) will result in energy savings because the less the temperature difference between the indoors and the outdoors, the less the heat loss.
-- The longer the set-back time, and the greater the set-back temperature, the greater the resulting savings.
-- Furnaces do not work harder, but output heat at a constant temperature until the thermostat senses the target temperature. The greater the difference between the actual temperature and the desired temperature, the longer the furnace will run, but it will be less than if it maintained the higher temperature all day or night long.
-- However, water radiator heated houses are slower to catch up the set-back and have to be started earlier in the morning -- giving you less total savings. Houses with great thermal mass inside have the same problem. Standard houses with thin drywall between the inside air and the insulation will catch up a set back the quickest and allow for the greatest savings with furnace set-backs.
-- The amount that you set-back your furnace is best determined by your comfort level and not at a threshold of 7 degrees.
-- General rule of thumb: for an 8hr setback, = 1% energy savings for every 1degree F set-back

With regards to the OP , I would go with leaving things alone since there is a comparator control system involved with a boiler.

hvhehcca
Re: to "turn" or not to "turn" down thermostat to save $$$

[QUOTE=LeonardHomes]
-- Any amount of temperature set-back (either done manually or through a programmable thermostat) will result in energy savings because the less the temperature difference between the indoors and the outdoors, the less the heat loss.

The difference in the heat loss. Is it really that significant. Yes it is. To figure out the heat loss through an outside panel the formula is simple

Ti-To divided by RV = btu sqft

Ti = Temperature Indoor
To = Temperature Outdoor
RV = R-Value of the Outside Panel

I live in a climate that has a zero outdoor temp so I'll use o degrees as my outside temp. I'll also use R-19 as my r-value you can stick whichever r-value you want.

(70 - 0)/19 = 3.68 btu's sqft
(65 - 0)/19 = 3.42 btu's sqft
(63 - 0)/19 = 3.31 btu's sqft
(60 - 0)/19 = 3.15 btu's sqft

As you can see the heat loss through the panel does change as Leonard has said. The use of setback with a traditional heating system can produce significant savings. But setting back a heating system that relies on indoor temp feedback and utilizing outdoor reset is not a good thing. Your basically fighting against each other and can expect huge swings in the ability to provide comfort.

canuk
Re: to "turn" or not to "turn" down thermostat to save $$$

I absolutlely agree , generally speaking , setting back temperatures has a great benefit. I don't know where the 7 degree figure comes from either , and the HVAC efficency is not compromised by a greater set back.
Bottom line---- the lower the temperature ( that your comfort allows ) for a longer period the more benefit of fuel savings ( $$$ ).

jim hankinson
Re: to "turn" or not to "turn" down thermostat to save $$$

Temp setback can save fuel if not done to excess. If you have a heating system that is accurately sized to your heat loss then on a design day the temp may not recover. If you have hot water heat sometimes having the heat off for too long can result in frozen pipes along outside walls or in areas that may have air infiltration from outside. The plumbing repair will be considerably more expense than the fuel saved.

pomer
Re: to "turn" or not to "turn" down thermostat to save $$$

here is the answer to the old snake oil question so you can answer your own question buy an hour meter wire it in to your boiler/furnace burner monitor it both ways!!!!
mine runs better picking temp and leaving it alone.
everybodys application is 100% different

HoustonRemodeler
Re: to "turn" or not to "turn" down thermostat to save $$$

I was told about the 7 degree setback rule by my late father-in-law who was an engineer for PE&G for 40 years. Since he was more of a practical in-the-field kind of guy, I took his word for it.

Your home and preferences will be different than the house next door. Do some monitoring, write down the usage, track the results, and make an informed decision.

Sten
Re: to "turn" or not to "turn" down thermostat to save $$$

It's not to hard to figure out, all you have to do is find out how many times your furnace cycles in an hour, one the coldest day mine fires three times in an hour and runs for about 8-10 min. per. Then I figured the amount of time it was off x 3, so if it was off for 5 hours I would multiply 3 x 5 = 15 cycles, then 15 x 9 (or the mean of the cycle time) = 135 min. So if my furnace takes more than 135 min. to get back up to temp after being off for 5 hours then wouldn't it be more economical to let it run all night? :confused:

I should have added that those nos. are with my stat turned down to 62 degrees at night and up to 69 when I get up.

canuk
Re: to "turn" or not to "turn" down thermostat to save $$$

Geez --- I would hope it doesn't run for 135 minutes straight to get up to temp.

I have my night time temperature at 60 and day time at 66 and at our cold temps ( -30 , -40 , -50 ) this results in about 35+% savings if I have the temp set at 70.

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