Is turning down the heat worth it?

[nate379]

I have radiant heat in my house. I know common sense would say the colder the house, the less energy needed to heat it... but here is my dilemma...


Last night, I set my thermostats to put the house at 60* when I'm not home and 67* when I am.

So 10PM it kicks down to 60* and at 7:30AM it kicks back to 67*. The paperwork that came with the T Stats said it would fire the boiler prior to that time so at 7:30 it would be at the right temp.

Well I got home at 8 and it was 64* in the house. It's 9:45 now and it's right around 67*. So the heat has been running more or less running for 2hrs.

Does 2 hrs of non stop override 8hrs of not running??

 

[rieferman]

I have the same capability with my thermostat... but at the time I schedule a certain temp, my house is that temp.. exactly. And it never takes anywhere near 2 hours of constant running to get there. I'm not saying yours is working incorrectly, I'm just giving you another point of view to reference against.

 

[nate379]

Takes a while for the slab to warm back up I guess. I could kick up the boiler temp a little bit though.

 

[rieferman]

ahh, didn't realize you were on a slab, that'd change the equation I'll bet. My house is on top of a basement, forced air heat. I can get from 60 to 70 degrees in about 15 - 20 minutes or so.

 

[nate379]

Fixed the thread, thought I had that in there that is was radiant heat.

 

[D KRAGER]

I would think with forced air only does it really help. On a system with slow recovery time system, I wouldn't change it. My parents have a new geothermal system, you set it and forget it!

 

[litljay]

It's usually cheaper to maintain a temperature than to either reduce (summer) or heat it up.

7 degree swing is fairly large and it may be in your best interest to reduce the difference between your "away" temp and your "home" temp.

 

[tdkkart]

I would say that a slab is a way different situation than regular radiant under floor. Once you loose the heat in a slab it takes a LONG time to get it back, burns alot of BTU's to raise a slab.
Forced air is a different story, I'm a firm believer in setback thermostats with forced air.
Years ago a neigbor and couple other friends were complaring gas bills month to month. I installed a setback 'stat, comparing to everyone else based on previous months,I saved 30% the first month.

 

[jeff5295]

I've always heard that you don't want to try and vary a slab temp. Radiant slabs are most efficient when operating at a constant temp. My guess is you're wasting more energy taking your temps up and down vs just setting it at 67. Or, as said earlier, try a smaller temperature swing. It takes a lot of energy to raise the slab temp, but not much to maintain a given temp (assuming you are properly insulated).

Give the smaller swing a try and let us know how it goes. Maybe just do 3 or 4 degrees.

 

[HoosierBuddy]

Set back t-stats can save a lot of money in some situations.

They are the highest bang for the buck improvement you can make in your energy use IF you use them properly AND it's the right application.

I don't think the OP's application is one of those that would benefit greatly from a setback thermostat though. They don't work well with heat pumps in general either, as if the resistance heat comes on they will eat up all the savings and then some.

Probably the place a set back t-stat will help the most is with a fuel burning forced air furnace. The less exterior insulation, the more the benefit would be.

Phil

 

[ixlr8]

In a forced hot air system, or a hot water radiator system, a set-back T-stat used properly is an energy savings device. A radiant heating system is not the place for a set-back T-stat. In a radiant system... set it and forget it. You will waste too much energy heating the slab/flooring back up and it will cost you more.

 

[southpier]

.....Once you loose the heat in a slab it takes a LONG time to get it back, burns alot of BTU's to raise a slab.....

the good news is that once you're up to temperature it takes a while for things to cool off. it's considered a "slow" building. usually an hour should do it but depends on loops of tubing in the floor. doesn't sound like there's a backup air handler w/ 2 stage thermostat. that way the hot air kicks in when the radiant isn't keeping up.

 

[Chetter]

I use a set back t-stat in my house and honestly, if you vary the high and low more than 4-5*, it negates any savings you are trying for since the furnace works longer to warm the air and furnishings to the high. I run only a 3* differance between my low at night and daytime high when I get home in the afternoon. I have seen savings from doing it that way and no savings when I went higher between my high and low temps.

 

[srmofo]

What I really want to know is how you reliably prove any savings. Theres just too many variables to consider from ambient outside airtemp, to wind speed and direction, to how many clouds are in the sky. It all makes a difference. How do you reliably compare?

I guess if you tracked all that and compared actual usage on the meter from similar day to similar day it would work.

 

[Gary S]

I have a setback thermostat, but I don't know if it saves any money or not. In the daytime I run it at 67 and at night we set it back to 63 because we can't sleep well with it at 67. It is too warm to be really comfortable.

 

[Blstr88]

I've always been under the impression, and have a great friend whos a mechanical engineer (not that that makes him a professional by any means, but he knows a little about heat/energy transfer) who swears its always in your benefit to turn the heat DOWN. Turning it down will save you money.

 

[tdkkart]

What I really want to know is how you reliably prove any savings. Theres just too many variables to consider from ambient outside airtemp, to wind speed and direction, to how many clouds are in the sky. It all makes a difference. How do you reliably compare?
I guess if you tracked all that and compared actual usage on the meter from similar day to similar day it would work.

In our case 3 or 4 of us were comparing bills monthly. With amazing accuracy, when one went up or down they all went up or down the same percentage.(3 of the houses were within 1/2 a block of each other, all in the same orientation) At the time all were using standard thermostats. The month after I installed my setback thermostat everyone else's bills went up 30% while mine stayed the same as the previous month. We even went back and re-compared billings.
Hardly a scientific test, but we all agreed that it showed a significant difference. The thermostat paid for itself in one month.

 

[olds70supreme]

Blstr88 Re: Is turning down the heat worth it?

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I've always been under the impression, and have a great friend whos a mechanical engineer (not that that makes him a professional by any means, but he knows a little about heat/energy transfer) who swears its always in your benefit to turn the heat DOWN. Turning it down will save you money.

I'm no expert in radiant heat systems, but going by the fundamentals your friend is absolutely correct. Regardless of what type of heat you have, heat transfer occurs at a greater rate with a greater temperature difference. If you keep the house at 80 degrees constantly, you are always losing heat energy at a greater rate than when you have it set to 70. One example mentioned earlier stated that the boiler/heater was running continuously for two hours, leading to the assumption that more energy was being wasted than if the temperature had been maintained for the last 8 hours. However, keep in mind that the boiler did have to maintain that temperature because the slab/house/whatever was loosing energy to the cooler surrounding environment during that time - aka the boiler did operate during the 8 hour period. The higher temperature over a period of time will lose more heat than a lower temperature over the same period of time, and since it takes energy/money to replenish the heat you lose more money at the higher temperature.

Please note that although the above is true, I don't know if a setback thermostat is correct for a boiler system on the grounds that it might be hard on the boiler to cycle up and down so frequently. Also, as the poster noticed, the amount of time previous to when the high temperature is desired may be tricky to find.

 

[sneezer41]

You do not setback a slab

You could do it for a few hours in the middle of the night, but it probably would not be worth the trouble.

 

[nate379]

I have it going down to 62 now and 67 is the high, I'll see how that works.

What I'm going to do is see how much gas I use in 24hr setup like that, vs leaving it at 67*.

 

[Chetter]

What I really want to know is how you reliably prove any savings. Theres just too many variables to consider from ambient outside airtemp, to wind speed and direction, to how many clouds are in the sky. It all makes a difference. How do you reliably compare?

I guess if you tracked all that and compared actual usage on the meter from similar day to similar day it would work.

That's the best way to see any savings, track it from previous years and if you have done nothing else to change things, such as insulation, etc. you'll have a good idea if it's working for you.

 

[HoosierBuddy]

I was at a meeting where utilities were comparing how various conservation programs were working, both in acceptance by the customer and by how much it actually saved.

They were really down on the set back t-stats, not because they DON'T WORK, but because they WON'T WORK if people don't program them and use them properly. It turns out that most people use it for a couple of weeks, then at some point they get cold so they set it on manual and enter a temperature and then the NEVER go back and turn it back to program mode.

The old set back t-stats had to be reprogrammed summer and winter (or your a/c would be "set back" to 65-degrees when you weren't home (I actually had that happen to me...and I'm supposed to know what I'm doing around the stuff).

My new setback t-stats have seperate settings for a/c and heat, which means you can pretty much program them and forget them. BUT...I've got mine at home set to manual because our schedule is so hectic that we don't know when we are going to be coming home AND our old house's upstairs bedrooms are colder all the time than I'd really like, so we can't even comfortably set it back at night.

So...my read on this after talking with "experts".

Setback t-stat = GOOD for a lot of people
a lot of people = BAD for set back t-stat because they use it improperly

All of that being said...if you have an old mercury t-stat...you will LOVE a new digital t-stat (set back or normal) because they control the temperature much more acurately. That should save you money too, because you are not overheating the home towards the end of the "heat on" cycle.

 

[nate379]

They are all digital T Stats. 1 for the living room, dining room, kitchen, 1 for the 2 bedrooms, 1 for the master and 1 for the garage.

No one is in the 2 bedrooms so I keep the doors closed and the heat at 45 in those. Garage is at 45 as well. (plenty warm to work on stuff and not break a sweat)

 

[redsky49]

All of that being said...if you have an old mercury t-stat...you will LOVE a new digital t-stat (set back or normal) because they control the temperature much more acurately. That should save you money too, because you are not overheating the home towards the end of the "heat on" cycle.

Hey, don't 'diss the mercury thermostat. A well made example will provide perfectly adequate temperature control, as far as accuracy is concerned. Many even had dual setpoints with two mercury capsules. As for convenience, the digital wins hands down. The closest that the analogs ever came was the old pin-on-the-timer versions such as Honeywell marketed for a number of years.

As long as you don't lose the Operating Manual for the digital thermostat, you'll be good to go. They all seem to have different requirements for programming - some easier than others.

That being said, I kinda miss the old pneumatic thermostats
(Inside joke I guess)

As always, offered only as opinion