Science-types - I have a curiosity about heating a home

[Inchworm]

Kind of a weird question, I admit, and probably easily debunked, but...

If your house is well insulated, wouldn't the cost of maintaining an internal temperature be the real close for a large range of temps?

Hmm, once the inside temp is set, wouldn't the furnace kick on just as much to maintain that temp?

:shrug:

[CreekDog]

1. it will take more energy to maintain a temperature farther from the outside temp

...than one closer to it.

[Inchworm]

2. But if the house is shut off from the outside

Doesn't that make it basically just maintaining a temp?

:D

I know it seems silly, but in my head.. it's tilted somehow.

:)

[NYC_SKP]

12. Lemme give it a shot.

This is up my alley...

In theory, you are correct.

Houses lose or gain heat (to or from the outside) in two ways:

1. Conduction through materials (this is where insulation comes in).

2. Convection through cracks, leaks, and opening doors, windows, the chimney, etc.

No home is completely "shut off from the outside" due to the above phenomena.

A super-insulated home that is also well-sealed would need very little energy to maintain the temperature even when the indoor/outdoor difference is great.

The more poorly insulated and sealed a home is, the more you're using your equipment to heat or cool the outdoors.

No home is completely shut off.

Building codes and practices through the last century have reflected the cheap cost of energy to heat them.

Other really effective design features like passive solar design and passive geothermal heating and cooling can make a home that stays comfortable for free or for very little cost for energy.

:patriot:

[Inchworm]

15. I see

That even clears my foggy brain a bit more (see post 14).

Even if the convection part is good on the exterior walls, that doesn't mean it is between floors inside :D

Thanks!

:hi:

[pokerfan]

25. Think of it as trying to maintain a water level in a leaky bucket

The more water in the bucket, the more pressure and the greater the rate of water loss. Like the water in the leaky bucket, the rate of heat loss from your home is proportional to the internal temperature. The higher the temperature, the greater the heat loss. Moral of the story: dial the thermostat down when you don't need it.

[Rabrrrrrr]

3. What do you mean "the real close"? Insulation as a selling point? i don't get it.

[Inchworm]

5. If your house is perfectly insulated

Is that like cutting it off from outside and making the inside its own air(?) that you are simply maintaining a temp of?

I'm asking here, because I really don't know the right question to ask so I can hunt the answer down needed to get the idea out of my skull.

:hi:

[Rabrrrrrr]

6. If your house is perfectly insulated, then it cannot be entered or exited

and whoever is on the inside will die of suffocation since there is no air exchange.

But, on the plus side, the body will never, ever rot.

[Inchworm]

8. ok

I'll leave a wee crack to allow the exchange of air if there are people inside.

Does that make a difference to the question? So what if people die in the house hehe.. would the energy use be the same at 60 degrees as it would be at 70 degrees once the temp is reached the first time?

:P

[Rabrrrrrr]

9. The simple answer is this - the better its insulated, the less energy it takes

to maintain a temperature versus a home that is lesser insulated. That is with making a lot of assumptions, though: the furnaces have equal efficiency, the houses have the same volume and geometry, the sunlight hitting them is the same, their roof area is the same and roofing material is the same, and so on and so on.


Now, the amount of energy that it takes to maintain that temperature depends on a number of things:

1) the efficiency of the furnace
2) the ductwork
3) the temperature you want to maintain
4) the outside temperature
5) the outside wind
6) outside sunlight and materials the house is made from and how they react to sunlight
7) how many times you're opening the doors and/or windows (that is, how often people or animals go in or out)
8) humidity outside, and humidity inside
9) how much air exchange the furnace does (which varies by geography, as cities/counties/states all have different standards about this)
10) the shape of the house, number of stories, and its location in relation to the land it is on (that is, under ground, above ground, partly both, elevated)

and, of course,

11) the insulation

[Inchworm]

14. Darn - that all is clear now

I have had the furnace set at 55 since daughter moved out (years). After she left my brother moved upstairs (years).

He is now gone (woohoo), and I thought about closing off parts of the house to be more efficient. I also wanted to raise temp to about 65 for a month or so to test cost/use.

I tried it for a day or two and what sucked was that the cold air coming in was coming in from the new closed off areas in the form of a cold ass breeze. I assumed this was all that heat rises thing.

I was just thinking the space between what I access and the outside walls as insulation (the closed off upstairs). I see that was where I was screwing up in my head. :P

I went back to 55.

Thanks.

:)

[TreasonousBastard]

4. The more insulated your house is...

the less energy (ok, money) it takes to maintain a given temperature. So, yeah, all things being equal, you would find a larger range than with a less insulated house.

But, all things are not equal and everything from the design of the house to its orientation and how it catches the sunlight affects things.

[Inchworm]

7. hmm

My use of the word range may have been wrong hehe.

You are agreeing with me it seems.

A well insulated home's energy use to maintain 60 degrees would be very close to the energy use to maintain 70 degrees.

A poorly insulated home's energy use to maintain 70 would be way higher than maintaining 60, right?

:)

[hobbit709]

10. Nope!

The higher you set the thermostat, the more energy it will take to keep it at that temperature because the heat loss has to be compensated for. The difference between inside and outside temperature coupled with the leakage factor, is what determines how much heat you have to replace.

[Schema Thing]

11. yes

why do you ask?

[Inchworm]

16. see 14

:silly:

[TreasonousBastard]

13. Well, yeah, close, but...

by how much?

I'd say "closer" than the uninsulated house, and installing good insulation and fixing the leaks (windows, door cracks, switchplates...) would possibly make it cheaper to keep the house warmer than the leaving it uninsulated.

All other things being equal, though-- and only a good energy audit will show you what will be really cost effective.

[applegrove]

17. That is an interesting question. I hear the Amish make great heaters. Try asking them.

[Inchworm]

20. Is there an Amish Group on DU?

It is where I ask all the tough questions :D

:hi:

[applegrove]

23. LOL!

[jmowreader]

18. Insulation just slows down heat flow

You know that insulation efficiency is rated in R-values. How these are measured is real simple to understand: they have two metal plates, one slightly warmer than the other. They stick a piece of insulation between them, then measure the temperature of the cooler plate. The number of hours it takes to cause the cooler plate to go up in temperature one degree Fahrenheit is the R-value.

[Inchworm]

21. SuhWEET!

I learned something else today!

Thanks!

:woohoo:

[BarenakedLady]

19. Just put some damn pants on.

:rofl:

[Inchworm]

22. LoL

Ya see.. that's why I tested the 65 setting. I realized I was getting to resistant to cold.

:rofl:

[quakerboy]

24. So, what you are asking is

if you have 2 identical very very well insulated homes, and you kept one at 65 and the other at 85, wouldn't they have close to the same energy usage to maintain that temperature, after achieving that temperature initially?

If that is your question, I would say no. First, your home, however insulated it is, is not that well insulated.

Second, as I recall from HS experiments, temperature change moves on a curve. The further away from the ambient, the quicker the energy tries to either enter or leave to bring about equilibrium. More insulation will alter the curve, but it is still a curve rather than linear. So if its 45 outside, your hypothetical matching houses are much more eager to dump the extra energy at +40 than at +20.

[Inchworm]

27. Zactly what I was asking

and you defined it well.

When I was thinking range I think I messed up a bit.

Now I wonder if a house itself has an "R" value. Also if that +20 part could play into thermostat settings.

Say 55 is what you set thermostat on when it is 0 to 20 outside. Would you use the same energy setting thermostat to 65 when it is 20 to 40 outside? Would tyhe "R" value of the home determine this? hehe

The more and more I think about it the more confuseder I get :D

:hi:

[quakerboy]

29. I think

again, basing it off of the good old fuzzily remembered HS experimentation and what I know of physics, via all too many chemistry classes and not a single actual physics class, that you would get a similar energy usage if its 20 out and you set it to 55, and if its 40 out and you set it to 65. Things try to reach equilibrium, a uniform condition throughout, and generally the further that they are from that, the harder they try to get to it(pardon my anthropomorphizing the forces of physics, please).

In my mind your houses are leaky water balloons. Heat is the water. If you fill it up(high heat), it sprays out all the holes rapidly to achieve pressure equilibrium. But if you don't fill it much(lower heat), it just kinda drizzles out. If you just barely fill it(lower heat), and put it underwater(higher outdoor temp), it doesn't even drizzle out so much.

[NJmaverick]

26. no (sorta), there are two basic factors that effect heat loss (or gain)

how well the home is insulated and the temperature difference. The greater the temperature difference the more heat is transfered (in or out, depending on the season). The amount of insulation will reduce the heat loss, but it will still happen.

That said, if you could super insulate your home, it's possible to make the temperature driven changes negligible.

[Inchworm]

28. Gotcha

Thanks.

I understand that now. I'm just a tad slow :)

:hi: