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Old 10-31-2011, 04:16 PM   #1
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2 Story House Temperatures


Hi all!

We have just installed 2 new furnaces in our 2-story 1837 home...converted from a single thermostat steam system. We needed 2 furnaces because the duct work did not allow for a single system.

So we have 2 thermostats, one on the main floor and one on the second floor. We are rarely upstairs during the day, so I'm thinking of setting the thermostat 2-3 degrees cooler upstairs than downstairs. But I'm wondering if this will even work, because heat will rise from the downstairs to the upstairs, and if the upstairs is cooler, it will just suck up more heat from the downstairs.

Am I making sense? Should I try this or just forget it and set everything at the same temp? We normally set our thermostats at 67 during the day and 63 at night. We have a Carrier ICS furnace, which just about runs constantly during the day with a slow to medium heat output...the only time high speed kicks in downstairs is during the early morning hours when the temp is below 35F. I have never heard the upstairs unit go into high speed.

Thanks for your suggestions!

John

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Old 10-31-2011, 05:57 PM   #2
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2 Story House Temperatures


It should never jump to the second stage, unless it runs too long to meet the load. For example, you set the thermostat to 62 at night, and the temp lowers to 62 by 6 am. At 6 am, you want to raise the temp to 68 degrees. Keep in mind, that heat rises, so the upstairs unit is set to start at 6 am, the downstairs is set at 6 am also. The downstairs jumps to stage 2 within 7 minutes, due to it still has not met the demand for it to go from 62 to 68 within the time that you expect. It should take no more than 20 minutes to meet the demand to raise from 62 to 68, any longer, then I would be looking at air leakage in the home.

With the downstairs unit finally starting to meet the demand within 10 min's, since heat rises, the upstairs is still in low speed, or stage 1, because the heat rising from downstairs is helping the unit to meet the demand upstairs, which in turn, is making that unit more efficient, because you are not burning as much fuel. Works even more efficient with a heat pump or geo-thermal for both units, but that is for another thread.

Over all, if your house is well insulated, air leaks are plugged up, your furnace should never have to kick into Stage 2 at all. An example is, we just went through and finally sealed some air leaks around our windows this past week. We do not have an insulated basement, but the rim joist & sill joist bays are insulated, nor are our walls insulated on the main floor, but they are air tight, along with all air leak areas sealed. The air temp is 65 down there, upstairs it has dropped to 62 in the past, before we did the air sealing. In the morning, when the furnace would raise the temp to 68, the ambient air temp would be 62, due to we drop it to 62 while in bed and away. The ambient air temp no longer gets down any lower than 65 at night, and when our furnace starts up, it only has to run in Stage 1 to bring it back up to 68. Even if I set the thermostat to 69, it only runs at Stage 1. That means that I am not only saving money, but my gas bill will be lower to the pocketbook, so no longer having to bend over backwards to pay to the man.

So going back, if the system is designed properly, and controls are set up as they should, to make it a efficient system, you should never see it jump into Stage 2 (high stage), unless you have it set back so low, such as going away on vacation for a extended period during Winter, then raising it to a more comfortable level, such as 68 or 70, depending on what you feel as the comfort level for you and your family.

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Old 10-31-2011, 06:07 PM   #3
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Its ok to set your upstairs cooler.
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Old 10-31-2011, 09:27 PM   #4
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Greg, thanks! I guess I really need to look at air sealing. Even tonight, with the outdoor temps only in the low 40s, the downstairs temp has dropped to 63 from 66 in 3 hours. We have a little insulation in our walls, but the downstairs does not hold heat at all. We have a cellar-like basement (stone walls, lots of air leakage). This house is so drafty...kinda hard to know where to start looking. All of the downstairs windows and doors are original to the house...which is a historic house in our neighborhood.

When you say that you sealed air leaks in your windows, what exactly did you do?

Thanks for any advice...appreciated.

Jbl

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Originally Posted by gregzoll View Post
It should never jump to the second stage, unless it runs too long to meet the load. For example, you set the thermostat to 62 at night, and the temp lowers to 62 by 6 am. At 6 am, you want to raise the temp to 68 degrees. Keep in mind, that heat rises, so the upstairs unit is set to start at 6 am, the downstairs is set at 6 am also. The downstairs jumps to stage 2 within 7 minutes, due to it still has not met the demand for it to go from 62 to 68 within the time that you expect. It should take no more than 20 minutes to meet the demand to raise from 62 to 68, any longer, then I would be looking at air leakage in the home.

With the downstairs unit finally starting to meet the demand within 10 min's, since heat rises, the upstairs is still in low speed, or stage 1, because the heat rising from downstairs is helping the unit to meet the demand upstairs, which in turn, is making that unit more efficient, because you are not burning as much fuel. Works even more efficient with a heat pump or geo-thermal for both units, but that is for another thread.

Over all, if your house is well insulated, air leaks are plugged up, your furnace should never have to kick into Stage 2 at all. An example is, we just went through and finally sealed some air leaks around our windows this past week. We do not have an insulated basement, but the rim joist & sill joist bays are insulated, nor are our walls insulated on the main floor, but they are air tight, along with all air leak areas sealed. The air temp is 65 down there, upstairs it has dropped to 62 in the past, before we did the air sealing. In the morning, when the furnace would raise the temp to 68, the ambient air temp would be 62, due to we drop it to 62 while in bed and away. The ambient air temp no longer gets down any lower than 65 at night, and when our furnace starts up, it only has to run in Stage 1 to bring it back up to 68. Even if I set the thermostat to 69, it only runs at Stage 1. That means that I am not only saving money, but my gas bill will be lower to the pocketbook, so no longer having to bend over backwards to pay to the man.

So going back, if the system is designed properly, and controls are set up as they should, to make it a efficient system, you should never see it jump into Stage 2 (high stage), unless you have it set back so low, such as going away on vacation for a extended period during Winter, then raising it to a more comfortable level, such as 68 or 70, depending on what you feel as the comfort level for you and your family.
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Its ok to set your upstairs cooler.
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Old 10-31-2011, 09:30 PM   #5
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2 Story House Temperatures


Thank you! I will try to set it a few degrees cooler. The downstairs unit in a 95% efficient unit, while the upstairs unit is only 80%, so that's a good thing.

Appreciate the response...

Jbl


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Its ok to set your upstairs cooler.
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