Trying to figure out what uses so much gas

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  #1  
Old 02-01-13, 06:44 PM
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Trying to figure out what uses so much gas

I'm trying to figure out what is using an inordinate amount of gas in my house. My gas usage is about 2x compared to the 100 neighboring houses with similar sq ft. all around me (according to PG&E). I have an okay-new gas furnace (new enough to not have a pilot, although I don't know its exact age), and I've done all the usual checking (i.e. making sure filters, returns, etc. are all fine).

I set my thermostat at 68F (since I like it cold), and it's programmed to be at 62F while I'm sleeping, and off during the day (when I'm at work). My gas water heater is fairly new, and I can't imagine that's the culprit since I don't use THAT much hot water.

So I started calculating. The furnace is 47,000 BTUs. PG&E claimed I used 140 therms last month. Estimating 20 therms for the water heater, I arrived at 255 hours of continuous gas input to the furnace. That's 8.5 hours a day. There's NO WAY that the furnace is on continuously for 8.5 hours a day, since the thermostat is really only on (and set at 68) for about 6 hours a day. I live in the bay area where the average outside temperature is in the high 50s last month.

So I can't seem to figure it out. It just seems like I'm way off. In the summer months, the gas usage is about normal, so I can't figure out what's wrong.

Is there a way to figure out why the furnace (I assume) is using so much more gas? I don't think any return path is clogged because the air flow is good. It sucks in lots of air. Vents pipes are all insulated. The hot air is okay--not super hot, but not bad. And the furnace heats up the house (~1200 sq ft.) from 62F to 68F in about 18 minutes.

The only thing I noticed is that the exhaust flue is VERY hot (burns to the touch), and seems much hotter than the actual vent pipes. Is that normal?
 
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Old 02-01-13, 06:54 PM
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This will take some of those better than myself, but I'll get you started.
When the gas burns it has two places to go, into the house or up the chimney. It sounds like a lot is going up the chimney, but I'm not sure what the normal hot should be.

When was the last time the furnace was cleaned. If the heat exchanger is dirty, it will have difficulty passing the heat to the air and thus much goes up and out.

What is your climate area in CA?
Are any of the heat ducts or returns passing through unconditioned spaces, like an attic or crawl space?

Bud
 
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Old 02-01-13, 08:28 PM
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Thanks, Bud. I'll have an HVAC guy look at that. That makes sense, since the hot air is not nearly as hot as that in my old house, and that furnace was way older. I actually don't know how long ago it has been cleaned, since I got the house last year. Before that, it was a rental so I suspect not much cleaning has happened.
 
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Old 02-01-13, 08:47 PM
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Gas hog

ottaflops:
A few years back they started to use the auto light Piezo igniters in gas furnaces and when they began that they started to improve on the rest of the furnace. One thing being the exhaust. Right now in residential heating the chimney is nothing more than PVC piping because the have run baffles in a series which uses the exhausted gasses over again by allowing them to stay in the heating chamber longer and utilizing the exhaust to it's full potential and then releasing it out of the chiminy. A great idea. With this in mind you might want to check the baffles to see if they have rotted through. If not then the chimney blockage is the only other reason as the other fellow stated. Good luck herbdogs
 
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Old 02-01-13, 09:07 PM
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Have your tech "clock" the gas meter to see what the furnace is actually consuming. It is possible the gas pressure regulator (built in to the gas control valve) is shot and the furnace is firing at a much greater rate than it should. Google clocking a gas meter if you want to do-it-yourself.
 
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Old 02-01-13, 10:14 PM
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Thanks, herbdogs, Furd.

Hm, I clocked the gas meter and it's almost exactly right.

* However, I just double-checked and my furnace is actually 80,000 BTUs (and not 47,000 BTUs). It's an American Standard Freedom 80, with four burners, and the label inside says it was made in 2004, and it's 80,000 BTUs.

Now my house is < 1200 sq ft. That's 67 BTUs/sq ft. Isn't that complete overkill for any zone? I'm in northern California (zone 2), so shouldn't I be at around 35-40 BTUs/sq ft (?).

Might that be the reason why I'm using so much gas compared to my neighbors?

But if my furnace is so oversized, should it still take 18 minutes to heat the house from 62 to 68?

Anyway, I'll get an HVAC guy to do a checkup, and check the baffles, and heat exchanger.
 
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Old 02-02-13, 11:25 AM
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Check with your gas utility to see if they will inspect your equipment for defects that might be wasting gas.

The utility I used to work for as a repairman offered that. In doing a lot of inspections like that, almost never did I find a furnace that was "wasting" gas.

A furnace that is defective and wasting gas will very soon get sooted up and stop working.

For pretty much anything else, the furnace is burmning the gas and if it doesn't get rid of the heat it will overheat and shut off on the limit switch.

So very likely you are using the gas.

Still having a competent rep[airman inspect and maintain the furnace is something that should be done every couple of years anyway. There are things that can be wrong, and a repairman may be able to help you identify ways to save.


If you really want to know how you are using your gas, you need to learn to read you gas meter and then start reading the meter daily for a while to understand how you are using gas, then perhaps several times during the day to see when you are using gas duiring the day.

If you maintain such records for a while, you can learn a lot about how you are using gas.

And frankly, it's worthless to compare your gas usage with someone elses by and large. Gas comsumption between similar houses can vary by a factor of ten --- even more, depending on the connsumption habits of different families.
 
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Old 02-05-13, 10:03 PM
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How old is the house?

Perhaps your neighbors have done energy efficiency upgrades over the last few years -> new windows, wall/attic insulation, air sealing, etc can have a very dramatic impact.

Some common renovations can actually increase gas consumptions -> for example, potlights improperly installed in second floor ceilings leak like a sieve.

Now my house is < 1200 sq ft. That's 67 BTUs/sq ft. Isn't that complete overkill for any zone? I'm in northern California (zone 2), so shouldn't I be at around 35-40 BTUs/sq ft (?).
Heat loss is determined by the exterior surface area (along with the usual factors - climate, insulation, construction type) rather than square footage.

Smaller homes need more heat per sq ft than larger homes.



But if my furnace is so oversized, should it still take 18 minutes to heat the house from 62 to 68?
...sounds grossly oversized. It should take at least an hour.


80 000 BTUs /hr (64k output) is an enormous amount of heat for a small house in california. On the coldest morning of the year, your furnace would run almost continuously to maintain 68 if it was properly sized.

Needless to say, in hotter climates, the smaller furnaces (40-60k) may not have large enough blowers for a/c.
 
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Old 02-05-13, 10:10 PM
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140 therms really is through the roof, given your climate. I would expect 140+ therms in climate zone 4 or 5.

Compare the dials on the gas meter to the last utility reading. They may have made a billing error.
 
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