Natural Gas Useage

[RagTop]

I can't seem to get a straight answer from anyone on this subject, so I'll throw it open for discussion. I live in Placer County, CA and I have gas service from PG&E. I am told that the responsible thing to do is to keep my thermostat at 68* to minimize my gas utilization and attendant costs. At 68* this house is like a big ice box. 72* is far more comfortable. My house is a single story with 2,489 sq. ft. of floor space and 9' ceilings. I believe that calculates to 22,401 cu. ft. of volume. My thermostat is a programmable set back type and, for the purpose of argument, comes on whenever the house drops below 68* by, say, 1. My contention is that the only difference between being set at 68 and 72* is the cost of raising the house from its nighttime temperature setting of 50* by an additional 4. I also contend that, whether the thermostat is set at 68 or 72, the cost of heating the house during the day and evening should be the same since, in either case, it is heating 22,401 cu. ft. of air by 1F and the house loses heat at the same rate whether the interior temp is 68* or 72. I have looked at several sources and I have determined that air weighs 0.075 lbs. per cu. ft. and that it takes 0.24 BTUs to heat a pound of air by 1F. By my calculation it would mean that I am using 403 BTUs to heat my home by one degree either way, and an additional 1,612 BTUs every morning to get to the 72* level in the morning. Am I missing something obvious here? I have no idea what PG&E charges for a BTU of heat but I do know that natural gas is in glut supply with the boom in American oil production.

 

[crustycurmudgeon]

the house loses heat at the same rate whether the interior temp is 68* or 72.

I'm certainly no expert, but it seems to me the house would lose heat at a faster rate from 72° than from 68°. As the temperature approaches the outside temperature, the rate of cooling would slow. I don't know what effect this would have on your calculations, though.

 

[RagTop]

Since the house has a finite number of "leak" points, they won't get any bigger whether the house's internal temp is 68* or 72* and, if the thermostat kicks in at the same point relative to the set temp, how would it cost more to heat 22,401 cu. ft. from 67* to 68* or from 71* to 72*? It still uses the same number of BTUs to do that.

 

[Horseplay]

I think at some point particular laws of thermodynamics come into play and the temperature variance from inside to outside temp do come into play, I believe. it should be noted, I'm not a thermodynamic physicist in real life but I do occasionally stay at a Holiday Inn Express so take it for what its worth.

On another note, 72?! I live in Midwest where we have seen temps in the -20s this winter and I set my thermostat at 69-70 in the winter. 72 is too warm an indoor setting. Put on a sweater or something!

 

[B67FSTB]

DRAFT is the word I think.
Beside insulation , you should look for draft and minimize it. It doesn't have to be zero draft cause then you need a ventilation system.
In a passive house , a house with a vent system , 68°f is very comfortable.
2 eurocent

 

[stangg]

Eliminate drafts for sure! If the air is dry and you heat by forced hot air, as soon as the heat shuts off you almost immediately feel a chill. A humidifier helps. I gave up on trying to run thermostats low and infrequently. I now set the heat to come on early so that it's easier to get out of a comfy bed, and actually helps keep the temps at a comfortable range throughout the day. It's 20 degrees outside today, and the furnace has only kicked on about 4 times through the daytime hours. It seems that it's harder in the early part of the cold season to keep the house warm. but once it gets warmed up, it seems the furnace works less to keep it at temp due to all the heat soak into things like gypsum, tiles, brick etc...
We were/are considering replacing our forced hot air furnace with forced hot water baseboard radiators to reduce the variation. Baseboard radiator are slower to heat the house, but much more comfortable. In any event, set the temp to what feels comfortable. I don't trust the actual readings on most thermometers. Its not uncommon to set our different zones with different set points.

 

[Midlife]

Bah! Heat transfer is a function of the flow rate of air from hot to cold, and the temperature difference. If the flow rate is constant (e.g. due to drafts), then heat loss is greater when the temperature difference is higher (i.e. hotter inside than colder outside). The gas usage to replace the heat loss will thus be greater to accommodate the greater heat loss. So yes, your gas bill will be lower if you set your thermostat at 68 vice 72.

That being said, if you could control the outside temperature to be 4* higher outside, then you can raise the thermostat to 72.

 

[JeffTepper]

Ken:

As I understand it, heating and cooling is a function of the transfer of heat from one area (the inside) to another area (the outside). The differential between temperatures in those two areas effects the rate at which the temperature is raised or lowered during normal furnace operation. That rate is variable and the calculations needed to project energy use can probably be found in Title 24 of the building code or in some HVAC design software program.

Since PGE maintains the pipeline delivery system but does NOT produce the natural gas itself, PG&E is a customer in the open market and passes on its cost plus mark up to the rate payer. Keeping profits up requires keeping costs down which generally requires conservation. Consider that the rate charged per unit of natural gas (therms) varies by volume, and the cost to you, the rate payer, goes up as your use rises from base line to Tier 1 to Tier 2 and so on . Essentially providing a disincentive in the way of tiered rates serves to discourage the rate payer from setting the thermostat solely on the basis of comfort. With most rate payers the choice amounts to a balance between cost and comfort. Only you can decide where on that spectrum you prefer to reside.

Lastly, if rate payers are too good at conservation, the revenue projections from operations will fall short and the utility will be seeking a rate hike from the PUC to offset that "lost" revenue. At least that is how is works with the local water company around here.

Regards, Jeff

 

[Horseplay]

There is something just so basically wrong when the volume user pays more than the minor. Where else do you pay more to get something in bulk?

 

[msell66]

There is something just so basically wrong when the volume user pays more than the minor. Where else do you pay more to get something in bulk?

And what other "business" tells its customers to use less of its product. What the fuck is wrong with Kalifornica?? BTW, I keep the house at 74* during the day and 68* at night. Burning the precious at c2.