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GalFriday 12-29-2010 06:44 AM

Help me understand my furnace and home heating
This winter I have been EXTREMELY vigilant about the thermostat. Last year's heating bill we got in January was astronomical (our first year in this house) and I'm trying to make sure it doesn't happen again.

"Everyone" says that just by turning down the thermostat a couple of degrees, I'll save lots of money. Well, I turn down, and last month's bill was $70 more than last year. So can someone please explain to me how this whole thing works?

We have an 80/20 furnace, two years old. The house is an older home built in 1950. Apart from one room with temperature problems (it does not contain the thermostat), the rest of the house seems to stay warm in the winter and cool in the summer (without the use of a/c) just fine.

Last year the thermostat was set around 70. Since the heater has had to be on this winter, I keep it around 65-67. Which is why I'm shocked that my bill is so much more than last year. Even with rate hikes, it shouldn't be that much.

Yesterday I decided to really pay attention to when the furnace comes on and when it shuts off. Generally, it turns on, runs for about 12 minutes, shuts off. 30 minutes later, it does it again.

Now, in my brain, I would think that if I lower the temp, the furnace shouldn't run as long, because it doesn't have to heat up to a higher temp. Therefore, heating at 60 should be shorter than heating at 67. So I dropped the temp in my house to about 60. But there was no difference in the cycling. It was just the same. Why?

Help me understand this. I don't think I'm stupid, but maybe I am when it comes to the furnace. I feel like the only way I am going to be able to control my bill is by shutting off the furnace completely for several hours each day.

DangerMouse 12-29-2010 06:55 AM

Don't feel like you're all alone, I'm home by myself most of the week, so I set the t-stat to 50 and wear my one piece hunting quilts to stay warm.
We also have a woodstove, but I'm getting older and cannot go out to the woods and drag up firewood as often. However, when I do, that helps keep the furnace from starting up too. Even having a new 95% FE furnace doesn't seem to matter, we still go through propane like it was going out of style, and as expensive as it is...... Your best bet is to check for anywhere drafting may be occurring. Insulate, insulate, insulate!
KEEP the warmth you're paying for as long as possible!


gregzoll 12-29-2010 07:42 AM

You never stated what your billing average is, nor what the bill amount you are comparing to, from last year to this year. If you are concerned if your unit is sized properly, or working properly, get the company in that installed it to look at it. Sounds more like the thermostat may not be set up properly. What really gets me, is the amount of people that come asking questions on the Interwebs, wanting free advice, but never go out and have a company come in first to look at the situation.

To have a company come in and look at the unit and thermostat could run you anywhere around $100-200, but asking questions and doing nothing about it, can cost you thousands, plus not give you the real info, because no one is able to physically touch the system to tell you what is wrong.

GalFriday 12-29-2010 08:18 AM

Well thanks for the rather rude reply. The whole point of forums such as this is for people who have QUESTIONS to come and ASK them. If you don't like my question, don't respond. I'm not looking for someone to do virtual repair. I don't need repair. I'm looking for some explanation of how the system works, so that I can better understand my furnace and my home. Then I can correct my own problems whether on my own or through a service provider.

I don't have a span of average billing - this is only our second year here, which I stated, and therefore I can only compare to last year.

Daniel Holzman 12-29-2010 08:55 AM

Not sure what type of heating system you have. It would be easier to discuss if you describe in some detail what you have. In particular, forced air, hot water or steam, the name and description of the furnace or boiler, the type of piping you have, the type of thermostat you have.

I have a hot water boiler with forced hot water heat that runs off fuel oil. The internal temperature maintained by the boiler is adjusted via a control on the boiler. Mine is set to maintain the boiler water at about 150 degrees F. When the thermostat calls for heat, it means that the temperature inside the house has fallen below the set point on the thermostate. For example, if the thermostat is set to 68 degrees F, when the thermostat senses that the air in the room is less than 68 degrees, the pumps on the boiler turn on and hot water is circulated around the house.

The water circulates until the temperature in the room exceeds 68 degrees, at which time the pumps are shut off by the thermostat. The cycle time is the amount of time it takes to bring the temperature above the set point. In my case, the cycle time is the amount of time it takes to add two degrees to the house temperature (67 F to 69 F). Different thermostats have different tolerances, so cycle time is a function of the thermostat, and how quickly you heat system can deliver heat to the house. My cycle time is about 15 minutes.

The amount of time it takes for the house to cool down to below the set point is a function of how cold it is outside, and what the house temperature is. The house will cool down more rapidly if there is a greater temperature difference between the inside and outside. For example, if you set your thermostat to 70 degrees, and it is 40 degrees outside, the delta is 30 degrees. If you set your thermostat to 55 degrees, the delta would be 15 degrees, and the rate of cooling would be half that for the 70 degrees case.

Note that the cycle time for the furnace remains the same, since you still have to raise the house temperature about two degrees (at least for my thermostat) to get the furnace to shut off. So the reason a cooler house in winter is more efficient is due to the longer cool down cycle, and is not related to the warm up cycle. In fact, if you set the house temperature to the outside temperature, the house would in theory remain at the same termperature, and you would not need your furnace at all.

As to why you are paying more this year than last year, despite having a lower set point, there are a few possible reasons:

1. The price of fuel for the furnace is higher.
2. The outside temperature has been lower.
3. You have a leaky door or window.
4. The furnace needs to be cleaned or serviced and is running at lower than ideal efficiency.

shoothebunnies 12-30-2010 10:19 PM

We cut our cycling down with the following improvements:

1. Using Pro Seal duct sealer to seal all of the connections on the trunk line and every take off going to a register. You would not believe how much this has improved the efficiency of our system! Very easy to do, pick up a bucket and a paint brush and go to town.

2. Check all windows with a match test to see if drafty, if so caulk or foam etc... to seal.

3. Insulate above lay in ceilings if you have them.

4. Put lined drapes up in front of your windows, and switch to energy efficient blinds. This step cost more than any of the above but also makes a huge difference .

5. Use a warm air humidifier if you use one. Cold airs are great and good for kids. We use a cold air when the kids are awake and turn on the warm air overnight. It raises the temp by putting steam in the air, and in the winter here it is miserably dry anyway so it has two benefits!

I hope this helps you in your quest for a cheap, warm, efficient HVAC system.

Have a great day.
Willis :thumbsup:

beenthere 12-31-2010 05:26 AM

Whats an 80/20 furnace?

Its possible, that the higher bill you got was due to higher rates, and a colder outdoor temp.

The cycling of your system, may be in part due to the type of thermostat, you have.

Post the size and type of house you have, along with its age and general location(so we have an idea of your weather/temps). Also the brand name and model of your furnace, and its serial number would help. Knowing brand and model of thermostat will tell us how it determines when to turn the furnace on and off.

If your furnace has its ducts in the basement or attic, and if that area is heated or not, knowing this will also help us help you.

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