Turned on the Heat

I broke down and turned on the heat today. I’m not sure why, but knowing when I turn the heat on each year is of interest to me.

I’m not sure how useful it is to compare since this is now looking at two different houses, but whatever. Each year’s weather patterns change as well, so it doesn’t mean that much. Last week it got so warm we turned on the AC and now the heat’s on.

Another heating oddity–our new house as a high efficiency furnace. The previous owner told us it’s more efficient to set the furnace at whatever temperature you want and leave it there. Turning it down at night wastes energy because it takes more energy for the furnace to heat the house back up than it does to simply maintain the temperature. It has something to do with the furnace kicking into a higher burn. Seems odd to me. I can understand it if you turn it from 72 down to 62 at night, but what if you do something more gradual, say 70 down to 66? It just seems unnatural that turning the heat up is using less energy (it also makes having not one but two fireplaces seem kind of pointless).

Update: I asked a furnace guy this question and he said that’s ridiculous. Turn it down at night and save some energy.

3 thoughts on “Turned on the Heat”

  1. Your house’s previous owner is most likely mistaken. If you had a heat pump it would make sense, because beyond a certain set-point, most heat pumps will switch on auxiliary heat which is typically electric base-board or something drastically more expensive.

    Here in MN however, I’m sure you have a standard forced air. Not an expert, but I believe the only real variable is fan speed. The burners are typically only on, or not on. Otherwise you’d have issues with the heat handling capability of the heat exchanger. With forced air, programmable thermostats or manual set-back is an extremely easy way to save money because furnace run-time maps directly to money spent.

    Also, keep in mind that due to Newton’s laws of thermodynamics keeping a smaller temperature differential between your house and the outside world reduces the slope of the heat-loss curve and means that the furnace does not need to work as long to keep the system at a fixed temperature

  2. Well, that’s just it, according to the previous owner there is another variable for the forced air furnace–two different burn cycles. If it kicks on to the higher burn cycle–like it would in the morning when it goes from 64 to 71 for example–it would use the higher cycle which is less efficient than keeping it at 71 all night using the low burn cycle. That’s how he explained it anyway.

  3. Hmm, never heard of such a thing. I guess it could be possible. So we could give it the sniff test of plausibility. A different burn cycle would mean either a variable aperture burner, or multiple sets of burners. That seems an unlikely way to design a furnace.

    Heat pump systems as I mentioned require an auxiliary system because they are relatively ineffective at changing temperature rapidly and with large gaps to make up may not even be able to raise the temperature fast enough for it to matter. Gas furnaces on the other hand, even small ones are quite effective.

    Because heat generation tends to be near 100% efficient, the only real reason to generate more heat from a gas furnace would be to warm things up faster. Faster heat-up I believe would just be faster however, not consume more gas because the temperature differential to make-up would still be the same.

    Not that the whole discussion really matters. I still think you’d get lower gas bills if you use set-back. You’d have to talk to an HVAC guy instead of me to get the truth of the matter though I suppose. Even if it is slightly less efficient, the reduced effort to keep the house at a lower temperature would probably make up for it.

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