AC vs heat

[kdm31091]

I hear conflicting reports. Which one ends up being cheaper?

I would think AC is cheaper, because when the outdoor temp is 95 and you're cooling it to about 70 inside, that means the machine changes the temp by 25. If it's 10 degrees and you're heating to 70, the machine has to change the temp by 60. Not sure if this matters, but it seems like AC is cheaper. Could be one pro of me going to Florida, if that's the place I choose!

[Wyoming53]

Originally Posted by kdm31091

I hear conflicting reports. Which one ends up being cheaper?

I would think AC is cheaper, because when the outdoor temp is 95 and you're cooling it to about 70 inside, that means the machine changes the temp by 25. If it's 10 degrees and you're heating to 70, the machine has to change the temp by 60. Not sure if this matters, but it seems like AC is cheaper. Could be one pro of me going to Florida, if that's the place I choose!

kdm, it's called efficiency. haha You are correct in your thoughts. But, it, just, don't, work, that, way. haha

I have central air. Live up in Wyoming so we get the -40 and we get the 105 in the shade. Like you, I would think that to lower it by 20 degrees is much cheaper then raising it by 100 degrees. Not necessarily so.

Air conditioners are engergy hogs. Running that big compressor for long periods of time is costly. Running that squirril cage in the furnace, is relatively cheap in comparison.

It's funny, they have a program here where they will average your bill for one year, divide it by 12 and then you can pay a fixed amount. (it varies a little when they make adjustments by not a significant difference. That way you can kind of plan your bills a little easier. My bill last summer with the AC on, was about $150 a month. This winter, about $154 a month.

Now the reason I say it is more costly is that in the winter, again, I'm raising it by at least 80 degrees. In the summer, I'm lowering the temp by 20 degrees. So your price by degree is much more expensive. Also, in the winter, I'm using gas and electric to heat it. In the summer, I'm only using electric. Well, and of course, gas for the stove all year.

[Wyoming53]

kdm,

I forgot to mention something. A friend of mine has a comperable home. Same size, almost the same layout. Only his house is all electric. He actually pays more then I do. Course, I don't know if he's winterized or insulated his home like I have done to this one.

[the dufferz]

Originally Posted by kdm31091

I hear conflicting reports. Which one ends up being cheaper?

I would think AC is cheaper, because when the outdoor temp is 95 and you're cooling it to about 70 inside, that means the machine changes the temp by 25. If it's 10 degrees and you're heating to 70, the machine has to change the temp by 60. Not sure if this matters, but it seems like AC is cheaper. Could be one pro of me going to Florida, if that's the place I choose!

It's a weird one to compare. In Washington it a luxury, in the south it's manditory.

One factor that most people don't think about is the effect of radiant heat. Here is how to look at this. All day long the sun is drenching the roof, walls, windows, everything with pure radiant heat. After the sun goes down, the house envelope is still saturated with heat, like a rock that was next to a fire is still warm to hot for hours. Once the radiant heat penitrates the interior envelope, then all your interior walls and ceiling becomes a heat source to the inside of the house. this can takes hours to overcome with an A/C unit.

While the temperature is less than you have in the winter, comparing indoor to outdoor comparison, If you go into your attic on a day when it is 95 degrees, the attic very well can exceed 160 degrees. That's a 90 degree difference between that and a 70 degree interior temp, so it like having a winter time low of -20.

Sorry for the less than encouraging news.

[scirocco22]

Originally Posted by the dufferz

It's a weird one to compare. In Washington it a luxury, in the south it's manditory.

One factor that most people don't think about is the effect of radiant heat. Here is how to look at this. All day long the sun is drenching the roof, walls, windows, everything with pure radiant heat. After the sun goes down, the house envelope is still saturated with heat, like a rock that was next to a fire is still warm to hot for hours. Once the radiant heat penitrates the interior envelope, then all your interior walls and ceiling becomes a heat source to the inside of the house. this can takes hours to overcome with an A/C unit.

While the temperature is less than you have in the winter, comparing indoor to outdoor comparison, If you go into your attic on a day when it is 95 degrees, the attic very well can exceed 160 degrees. That's a 90 degree difference between that and a 70 degree interior temp, so it like having a winter time low of -20.

Sorry for the less than encouraging news.

Yeah, I concur with what you're saying.

A good example is when I moved to desert Nevada from western Washington, I was amazed that I didn't need to use the furnace on these winter nights where it gets into the low 20s --even 18 one night early in December.

Why? Because since it's sunny out during the day with temperature getting up into the 60s, it heats the inside of the house enough to keep in the 70s practically all night long. That, in addition to the insulation they use down here while keeping in mind the 115 degree summer days, helps to keep all that warmth in the house.

I just shake my head when I think it's the middle of winter and I look at the thermostat in the middle of the day and it's reading 85 degrees!

--'rocco

[the dufferz]

I know what you mean. We experiance that all of the time in western washington! hehehe.

[RodFarlee]

Originally Posted by the dufferz

While the temperature is less than you have in the winter, comparing indoor to outdoor comparison, If you go into your attic on a day when it is 95 degrees, the attic very well can exceed 160 degrees. That's a 90 degree difference between that and a 70 degree interior temp, so it like having a winter time low of -20.

Sorry for the less than encouraging news.

Attic ventilation should be improved if the attic temperature is more than about 20 F higher than the outside air temperature. Such high temperatures as that (160 F!) will substantially shorten the life of asphalt roofing and plywood roof sheathing.

Homes built before modern building codes mandated adequate attic ventilation can benefit. It is relatively easy to accomplish in a variety of ways. Convective cooling using ridge vents, added soffett vents, even a cupola or wind turbine vent will in nearly all cases keep the attic temperature no more than 20 F above the outside air temp. In particularly difficult cases, thermostated, powered exhaust fan vents may be needed. The effort is quickly recouped in lower air conditioning costs.

[RodFarlee]

Originally Posted by kdm31091

I hear conflicting reports. Which one ends up being cheaper?

Kevin, suggest you look up heating degree days and cooling degree days.
Maps of heating degree days and cooling degree days as well as additional maps and animations are available from the NOAA.

[Wyody]

Originally Posted by kdm31091

I hear conflicting reports. Which one ends up being cheaper?

I would think AC is cheaper, because when the outdoor temp is 95 and you're cooling it to about 70 inside, that means the machine changes the temp by 25. If it's 10 degrees and you're heating to 70, the machine has to change the temp by 60. Not sure if this matters, but it seems like AC is cheaper. Could be one pro of me going to Florida, if that's the place I choose!

Kev, you might recall I was pushing for you to select the coast. I rarely used the A/C because the coastal breezes coming thru the hurricane-windows (make sure you have them) was enough to keep my place cool enough. That's something to consider in your comparisons also as, when it's hot outside you can open your windows to catch breezes but when it's cold - opening your windows will not assist your heat-making machines!

[Curious George]

Hey woody I like the new avatar

[Wyody]

Originally Posted by Curious George

Hey woody I like the new avatar

Thanks! Got a million of 'em.

"... what's in that pipe that he's smoking?
Why do blue skies rain on these guys"? A. Guthrie - the Pause of Mr. Claus

And it helps that I'm Irish ... no wait, not s'posed to admit that 'cause I'm a Scot ... no, wait, more Welsh than either .... no, wait, French too ... well, wait a daggummed minute - I've got 5 English knights in my different lines so I must be a Briton? .... no wait - three Cherokees rambling thru my veins - I'm a Red man! .... well, as I say, got a million avatars and each one suits me!!
Thanks again,
Copy this Freq?

[the dufferz]

Originally Posted by RodFarlee

Attic ventilation should be improved if the attic temperature is more than about 20 F higher than the outside air temperature. Such high temperatures as that (160 F!) will substantially shorten the life of asphalt roofing and plywood roof sheathing.

Homes built before modern building codes mandated adequate attic ventilation can benefit. It is relatively easy to accomplish in a variety of ways. Convective cooling using ridge vents, added soffett vents, even a cupola or wind turbine vent will in nearly all cases keep the attic temperature no more than 20 F above the outside air temp. In particularly difficult cases, thermostated, powered exhaust fan vents may be needed. The effort is quickly recouped in lower air conditioning costs.

If the attic ventilation is passive, then other than convective currents, it takes a breeze to make the ventilation work. I have been in attics that were at code (our code, 1 sq. ft. vent to 300 sq. ft. attic, 1/2 intake, 1/2 exhaust) and even in washington it sweltering hot. The only other option would be to use active ventilation. In our area that is mostly wired for humidity, not tempurature.

When I replace my roof, I went with a ridge vent, and that helped.

[deeptrance]

My 2 cents on this:

In Texas, summer is the expensive season if you have gas or wood heat. But when I lived in a place with electric heat, my winter bill was higher.

Consider the physics and thermodynamics of heating vs. cooling: to heat something up is easy because heat is basically "wasted energy" that comes from normal processes. Cooling, however, is a much more technically difficult process to achieve. Merely having the lights and TV on in your house will heat it up. There is no such thing for cooling because the waste generated by energy use is almost entirely in the form of HEAT.

However, electric heat, at least the central forced-air system I had in my house, can be VERY expensive because you're basically using perfectly good electricity for nothing more than "waste." It's a very inefficient way to heat your home.

[RodFarlee]

Originally Posted by the dufferz

If the attic ventilation is passive, then other than convective currents, it takes a breeze to make the ventilation work. I have been in attics that were at code (our code, 1 sq. ft. vent to 300 sq. ft. attic, 1/2 intake, 1/2 exhaust) and even in washington it sweltering hot. The only other option would be to use active ventilation. In our area that is mostly wired for humidity, not tempurature.

When I replace my roof, I went with a ridge vent, and that helped.

Yes, the code is a minimum requirement. The minimum isn't adequate for low-pitched (3/12 prefab truss) roofs with dark shingles. Experts recommend double the vent area required by code.

I mentioned it because it can really make a dramatic difference rather easily, and it is a relatively easy DIY project.

I had an overheated attic, so put in one 12" wind turbine. It did the job of keeping the attic not more than 20-25 F above OAT, and kept the entire house about 10 F cooler in summer. Then 20 years later, I reroofed with lighter colored shingles, and installed additional soffet vents and full length ridge vent instead. That also worked. So "code" isn't necessarily good enough (or let's say it might be in Seattle, but not in Pasco).