Maybe OT: Save fuel with a setback thermostat?

spaco · 2010-12-04T23:37:23+00:00

If the fact that my furnace is metal qualifies for "metal content", then let it be so. If not, then this post is off topic. It could, however, relate to heating one's shop so----Anyway, here's the question:Does a setback thermostat really save you any fuel cost?For our house and the way we live, the answer is "hardly none". I hooked up a simple thermistor to the DAU (Data Acquisition Unit) that's hanging off the back of my computer and have been graphing "furnace-on" events for several days. We stay up till about midnight or so and then the thermostat goes from 74° F down to 65° F until morning. The thing is set to go back to 74° at 8AM, but it anticipates for us, so on real cold days it starts in as early as about 5:30AM. The amount of time it takes to get house back to 74°F is almost equal to the amount of time that the furnace would have been running if there was no setback. During the night, the house hasn't ever gotten down to 65°F before the furnace came out of setback. Some googling on the subject sorta confirms what I found. The general answer is: "it depends". They say that the worse your insulation, the more a setback thermostat can cut energy bills.My measurement process: I use a Radio Shack "Sensor Lab" to make up simple circuits. I bought a 9volt battery eliminator for it.I put the thermistor right on top of the closest wall register.The thermistor is simply in series with a 10K ohm pot across the 9 volt supply and I took the signal across the wiper arm of the pot and ground. These two leads connect to one of the inputs on my Dataq DI-194RS $25 (now $50) DAU, which connects to the computer through a serial port. The software that came with it makes the graphs. Only the top trace is active on the graphs referenced below. The units are volts. The range I chose is simply to give me a fairly full chart excursion. The peak voltage corresponds to about 108°F and the overnight min is about 63°F.Here's a link to a graph of...

Dec 04, 2010 23 Replies

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spaco 15 years ago

Yes, Type R was a favorite in the high temp (2200 F to 3000+ F) Vacuum heat treating furnaces. But we still used C/A (type K) in the workhorse machines---- 1800F to 2300F vacuum furnaces. Of course we didn't have the corrosion problems unless we were experimenting with partial pressures of various gases.

Pete Stanaitis

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Spehro Pefhany wrote:

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newb 15 years ago

And I have yet another data point to throw in this mix. Bigger is better. Three years ago I broke down and bought a 1,000 gal propane tank. It's a sub grade install. We're saving up to buy a 2nd one. Up here in the PNW, propane prices seem to vary wildly between Summer and Winter rates. With this much capacity I can buy low and make it over a year for the house. The additional 1,000 gal tank will be for my shop.

Two winters ago propane prices in the late fall were near $4.00 per gal. I'd filled it that Summer for less than $2.00 per gal. By next Spring the 1st tank will have paid for itself. The additional capacity with the 2nd tank will allow me to fine tune my buying timing. Figure that one can remain 1/2 empty to allow unforseen bargains.

Our goal is to have enough propane capacity to go totally off-grid, if need be, for over two years. In the meantime saving between 30-50% on our past three years heating bills works for me.

Newb

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