Need help tracking down high energy use

sjmayeJanuary 11, 2011

I bought a new home. It was built in 1996. Electrical energy use seems much higher than my previous house of about the same size. Is there an easy way to isolate where the energy is going?

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Haven't a clue where you live. A lot of things effect energy use. Different provider with higher rates. Less energy effecient windows and doors. Any idea of insulation
rates in various areas of the home. Perhaps you did things to your old home to mediate energy use. Just guesses with very limited information.

    Bookmark   January 11, 2011 at 8:29AM
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I live near Nashville, TN. My other home was a two story home. Total about 3000 sq ft. This is a single story home about 3000 sq ft. Other home had flat 9' ceilings. This one has 10' - 12' ceilings. Many tray ceilings and cathedral ceilings too.

I did nothing special building the other home. Pretty much about 8.5" fiberglass blown insulation. This has the same, but areas between the tray ceilings and eaves have almost no insulation. Appears the really did not try to cover these areas. In some places I see the drywall ceiling. I know this is obvious, but just trying to understand the other potential issues.

Power rates are the same for both homes. Both are heated with gas and cooled with electrical AC. Both homes were built about 1996.

    Bookmark   January 11, 2011 at 8:47AM
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I'd recommend finding an insulation contractor to tighten up the attic insulation. Otherwise, your new house has twice the ceiling area, so I'd expect it to perform poorly in comparison. There aren't many details here, but on first glance, I don't believe this is related to electrical efficiency or malfunction.

    Bookmark   January 11, 2011 at 9:02AM
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I thought the same thing. I have an estimate from a contractor. Seems reasonable, but not really sure what depth of insulation I should be asking for. He was basically talking of adding another 8.5" to the current 8.5".

    Bookmark   January 11, 2011 at 9:14AM
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You should ask him what R value that will give you and what R value is recommended for your area. Higher R value is better, but there are diminishing returns once you get above the recommendation.

If you really want to find where the power is going, you can do it systematically. Turn off all the circuits. Turn one on. Check the meter to see if/how much it is moving. Turn that back off. Repeat.

Really though, there are about a million things that impact electricity usage. You might want to google search energy efficiency etc There are lots of things you can do to maximize efficiency - keep fridge coils clean, replace HVAC filters to reduce strain on blowers etc. There is probably no silver bullet, but lots of little tweaks can add up to significant dollars.

    Bookmark   January 11, 2011 at 9:27AM
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I was trying to gauge the cost(for natural gas) when my furnace has run(consumed gas) for an hour's time. I did it two ways.
First I just took the BTU input rating of the furnace and did the calculations from there. Then someone pointed out that the BTU input rating may not be an actual value.

So secondly I needed to determine the amount of gas my furnace is actually consuming per hour.

Here are the particlars:
1. I have Goodman model GMPN100-4 furnace. (natural gas, single stage, pilotless and an input rating of 100,000 BTU per Hour)


1.One cubic foot of natural gas has about 1,030 BTU.

2.Divide the furnace input rating(in my case 100,000) by 1030 to get the number of cubic feet of gas the furnace will use in one hour. So 100,000(BTU) divided by 1030(BTU per Cubic Foot) is about 97 Cub Feet.

3.My supplier's bill is based on units of one hundred cubic feet(CCF) so I divide 97 cubic feet by 100 to determine how many CCF the furnace will burn per
hour. This turns out to be 0.97 CCF

4.My supplier charges $.745 per CCF so it costs me 0.97 times $.745 = $.72 per hour for natural gas for my furnace to run.


As stated above someone pointed out that the BTU input rating may not be an actual value. So I wanted to determine how much gas the furnace was consuming per hour.

My gas meter has a 2 cubic foot dial. I set a video cam in front of the gas meter in the morning knowing the furnace would be on for at least 20 minutes to bring the house up to temperature from the night's setback. The furnace did run for about 20 minutes but I stopped my readings at 10 minutes. Here are some findings:
In 5 minutes the furnace consumed 7.6 cubic feet of gas.
In 10 minutes the furnace consumed 15.2 cubic feet of gas.

So 15.2 cubic feet of gas in 10 minutes extrapolated out to 60 minutes would be 91.2 cubic feet gas per hour or 0.912 CCF/hr.

At $.745 per CCF the cost is about $.68 per hour.
From the input rating data (100,000 BTU/hr) I calcualted .97 CCF/hr. So the actual gas consumption was a little bit less that the input rating.

Now some Notes:
1. My gas bill is broken down to a charge for gas consumption, a customer service charge of like $21 a month and of course the tax on the consumption charge.
So it's pretty straightforward how much the gas costs per hundred cubic feet. This month gas was $.745 per CCF.

2. No other gas consuming appliances(oven, stovetop or hot water heater) were firing at the time of testing.

3. I understand that outside temp, thermostat setting and how well my home is insulated are factors as to HOW OFTEN the furnace will run. That wasn't my concern. I only wanted to know how much gas was consumed when the furnace ran for an hour. How that hour was achieved was not important. It could of been 60 continuous minutes or six 10-minutes cycles. In my case I took a 10 minute run cycle and multiplied that amount of gas usage by 6.

I have since I've hooked up the following 24V hour meter to the gas valve:

The meter progresses in tenths of an hour increments anytime the gas valve is open. I can tell how long the furnace runs each day, month or season. This helps with filter changes also. I've found that about every 125 hours the filter is dirty enough to be replaced.

I appreciate the comments.

    Bookmark   January 11, 2011 at 9:55AM
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If your gas furnace is forced air, the impeller is run by electricity. So you are not only paying for the gas to the furnace but electricity to run the fan.

    Bookmark   January 11, 2011 at 12:41PM
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I know but the point of my invest was to discover how much gas the furnace consumed per hour. Gas consumption is not affected by the inducer fan motor or blower fan motor

    Bookmark   January 11, 2011 at 4:48PM
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I'm not going to bore you with a lesson in thermodynamics, but trust me on this: adding 8.5" of insulation to 8.5" of insulation will do little to improve energy efficiency. It would probably cut your bill by 1-2%, because that first 8.5" is already cutting your heat loss by a huge amount. However, putting in insulation where you have little or none will make a big difference. Here's a rough example (not exact, but close enough): Think of your house as a big styrofoam container filled with water, and with some small holes in it: the water won't pass through the solid part of the container, but it will readily flow out of the small holes. It's the same with your heat loss.

Also, do you know how well the walls and floor are insulated? If they skimped on that, or missed a few areas, you could be losing large amounts of heat that way, too.

While it is true that a single story house will typically lose more heat than a two story house of the same square footage, I think you can cut way down on your heat loss if you get the house properly insulated. So, before you waste money having some guy come in and indiscriminantly dump a lot more insulation in the attic, you need to determine where the house most needs it. See about getting an energy conservation firm to come out with an infrared scanner. This will give you a visual confirmation of areas in the house (floor, walls, and attic) where the insulation is lacking. It will cost a couple of hundred bucks, but it will also help you figure out where to insulate more and where not to over-insulate. You may need to add more to the walls in some areas, for example, but that can be blown in with minimal damage if you just know where.

    Bookmark   January 12, 2011 at 4:51AM
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My local power company has an energy saving program where they come in and do a whole house evaluation along with recommendations. I am going to call them today.

    Bookmark   January 12, 2011 at 6:11AM
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Texas Utilities, (TXU), has a program where a group of 5 or 6 men come in and do the following; caulk all of your air ducts where they come through the ceiling, completly reseal exterior doors and put on new threshold seals, rebuild and seal your return air and pull off every swith and receptacle plate and put insulation under each one. The crew was here for five hours and it was completly free.

They pulled off our round air vents and there were major gaps where the air ducts come through the ceiling. They sealed all of the gaps and reinstalled the grills. They spent two hours resealing our return air system.

In addition, some years ago we had all of our windows replaced with vinyl thermopane double hung windows.

Bottom line, we live in good old hot Texas, in a 3,000 sq. ft. ranch and our highest bill in the hottest months is around $250.

    Bookmark   January 12, 2011 at 8:25AM
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That's an excellent idea. I actually thought to mention that, but I was posting at about 2 in the morning and I don't think all my brain cells were firing! Good luck, and please post back afterwards. I'd love to hear what they say.

    Bookmark   January 12, 2011 at 3:28PM
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"My local power company has an energy saving program where they come in and do a whole house evaluation along with recommendations. I am going to call them today.:"

Unless the fixes they do are related to the high use it may not make any difference.

Losses from the heating envelope can be a cost driver, but there are plenty of other things that can drive up electric usage.

    Bookmark   January 12, 2011 at 4:09PM
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The case or two of good caulk and case of spray foam is in order before any additional insulation is even considered. Here are a few steps.

Have someone do an audit and actually look at the infrared images yourself and best yet get pics for later use.

Seal every seam and connection in the air duct system with brush on mastic or mastic tape.. no regular foil tape as it does not stick or seal long term.

Seal every hole in the floor where a drain or water line goes through and every wire from the basement or crawlspace with foam or caulk.

Do the same thing in the attic before adding insulation. The first step to efficiency is stop the air movement.

Now would be the time to think about adding insulation and where to add it.

If you like watching your electric usage I highly recommend the T.E.D. 'The energy detective. It is a device that you clamp CT's around your main cables in the breaker box and two more hots and a ground. The other portion of the system plugs into an outlet by your computer that you plug an ethernet cable off your computer or router into and access how much energy that you are using and have used along with end of month projections.

Here is a link that might be useful: The Energy Detective

    Bookmark   January 12, 2011 at 11:58PM
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I have the home energy audit scheduled for Feb 3. May need to reschedule due to work travel. I like what a previous poster said their energy company did in having, for free, people come in sealing ducts etc. Mine audit is different. Have to pay $150 at time of audit. If you do any of the recommendations you get the $150 back and 50% of the cost of the work performed as long as it is done by one of the TVA certified contractors. I was going to the insulation done anyway, so no loss. Max rebate is $500 + the $150 for the audit.

    Bookmark   January 13, 2011 at 6:13AM
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