Turn thermostat down or leave steady?

Page 1 of 6  

Please forgive me while I troll for a moment.....
Is it energy saving to turn the thermostat down, when leaving the house? I mean, the furnace has to run to catch up when I get home. I have a way of looking at the matter. I'll explain my point of view after the argument is underway.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Oct 29, 8:22 am, "Stormin Mormon"

Yes, you save energy turning it down. In balance less heat is lost.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

To elaborate, heat loss slows as the house cools (delta T is lower) so it takes less energy to maintain the house at a lower temperature and then heat it back up again. Especially so if the house is not well insulated.
That said, I have not noticed any drop at all in my gas bills since installing a programmable thermostat :(
nate
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No, it takes too long to re-heat the boiler and all the water in the pipes, radiators, and floor tubing. It is always best to set it once and leave it there all winter. Too much energy is lost when all that water is asked to re-heat all the surfaces again. For example when I feel the return manifold from the coils under my concrete slab after the slab was allowed to cool, the return water is ice cold, all that energy to reheat the slab. No, bad asvice, best to keep it warm and leave it there, saves tons of energy.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
RickH wrote:

I hope that you were just kidding because obviously you are wrong! Just think for a minute.....if you were going to be gone for three months don't you think you would save energy if you turned your thermostat down? Well, the same would be true for a few hours, just not to the same extent.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

We use warm water here to shower. I'd say that a higher % of people use heat pumps or gas to heat rather than water. In your case, MAYBE it is cheaper to leave it on, but I think you are only quoting yourself, and no analytic studies by any testing agency. Can you find any said studies? I don't doubt that you believe what you say is true, I just think that it is not.
Steve
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Boiler installers never put daily "set back" thermostats on boilers, only forced air systems get those, and they tell you to set the thermostat once and leave it there.
The rules are completely different for radiant heated buidings vs air heated buildings.
In an air heated building you heat the air, in a radiant heated building you heat the building materials and that in turn heats the people. When you lose all that stored energy it costs a fortune to recover it back in boiler usage. There is nothing quite like the warmth of a radiant-heated house.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 29 Oct 2009 11:05:16 -0700 (PDT), RickH

Why did you assume the Mormon had a boiler?

It costs that same fortune and more to keep it hot without interruption. Maybe it's also unpleasant becuase it takes hours to heat up, but that's another story.

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hot water heat is very popular here.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Boilers are typically left hot, so there isn't a bunch of humidity in the boiler, rusting it out. And, boiler systems often do take a LONG time to recover temp.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Stormin Mormon wrote:

I usually think, forced hot air. Boiler, I don't know but imagine water in tank would keep fairly hot if not circulated. Thermodynamically, turning temperature down saves energy.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 30 Oct 2009 08:18:35 -0400, "Stormin Mormon"

Yeah, but do you have one? His first answer assumed you did.

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
My heat source is a 90% downflow hot air furnace.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

So the laws of themodynamics are different from system to system?
Heat its lost to the environment based on the difference in temperature between the heated space & the unheated space. As the temperature of the heated space falls, the heat loss also fails. When the temperature of the heated space falls to that of the unheated space, heat loss stops.
I believe you are confusing the "time" it takes to recover with "huge amounts of energy are required to re-heat everything".
If you were correct in your thinking (& oyu are not) the whole concept of temperature setback would not work (& it does).
cheers Bob
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I think part of this is because we tend to think of the heat needed to heat something from the outside temp to what we want inside. But what the furnace does most of the time is just replace heat that is lost to the outside. And still it runs a lot.
So it runs even more when it has gotten colder than normal inside, because it was on setback. But it has run not at all perhaps or much much less the entire time people were out and the thermostat was set back.
Looked at another way, the furnace is usually just raising the temp one or two degrees, from the temp at which it turns on, 67^? to where it turns off, 69^?, and still it runs a lot when we are home
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If left alone the boiler kicks on maybe once every 4-6 hours for only a short 5-10 minute period (maybe 4 or 5 recyclings of the entire water load).
If you let the house cool for 10 hours while at work, the boiler will have to run several hours to get all the floors (and house contents) heated again. This run is more than the sum amount of time the boiler would have been fired if you had just left it alone. You've never lived with a boiler have you? Air is low mass, it heats up very quickly, radiant heating of the building mass itself takes longer from the same starting temp as the air entering a forced-air system.
Yes, the "rules" are different for forced-air vs under-floor radiant heat, in practice, but not the laws of thermodynamics are not.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry Rick, you're mistaken...setback always saves energy, you're confusing recovery time, inconvenience & comfort with energy use.
Run the numbers, I'll give you a starting point.
Are we talking CI radiators, baseboard units or in floor radiant heat? Tube material? Estimate or determine the total amount the water in the system. Estimate the weight of the radiators & delivery system. Calc the thermal capacity of the water & the delivery system. Hint: The specific heat of water is 1 btu/lbm degF .... it is left as an exercise for the reader to determine Cp of the other materials in the system.
I think you'll be surprised how little heat is "contained" in the system.
So by your logic I should leave my mountain home heater thermostat set at 68F ALL the time? Day, night and when unoccupied because re- heating all the insulated mass of the house; drywall, flooring, floor framing and furnishings would take a "bunch of energy" ?
I don't think so...my fuel bill is high enough with the set back technique is play.
btw I have lived with boiler / steam heat :)
cheers Bob
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 30 Oct 2009 07:50:56 -0700 (PDT), RickH

Are you sure. You just said that the boiler it runs 5-10 minutes every 4 to 6 hours. So if you are gone for 10 hours, the maximum that the boiler wouldn't run would be 20 minutes.) Yet now you say it would take several hours to get the house heated again. Plainly it would take 20 minutes or less to get the boiler heated to it's normal temp, instead of just pretty hot for lack of 20 minutes of heating.
I don't have a boilerIs there more to the cycle that you think would delay heating the house?

No, it's not. You just assume that it is. Or it seems like it.

Of course it takes longer to heat up. It also takes longer to cool off, so it isn't as cold as the air is when you get home.

Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If left alone the boiler kicks on maybe once every 4-6 hours for only a short 5-10 minute period (maybe 4 or 5 recyclings of the entire water load).
If you let the house cool for 10 hours while at work, the boiler will have to run several hours to get all the floors (and house contents) heated again.
<<<<<
Your numbers cannot be correct.....
"left alone" it runs 10 minutes in 5 hours but "setback" for 10 hours ("let the house cool") and "the boiler will have to run several hours"
nonsense
cheers Bob
btw did you do those thermal mass / heat capacity calcs?
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 29 Oct 2009 11:05:16 -0700 (PDT), RickH

Sorry, but no matter what you do, if you lower the AVERAGE temperature over a long period, you save energy. That's the beginning, middle, and end of the facts. Your average temp over the entire heating season is what counts. Lowering the temp for a period each day results in a lower average temp over the course of a heating season.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.