Understanding temp swing settings/thermostat?

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Old 09-20-08, 05:08 AM
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Understanding temp swing settings/thermostat?

So, can someone explain what an optimum swing setting might be on my digital (Lux) themostat? (For Heating) Mine goes from 1-8. It is currently set at 1. My understanding is that the lower the setting, the more my boiler calls for heat to keep the set temp, but the boiler runs for only a short time. The higher the swing, the more the temp drops before the boiler kicks in, and then the boiler runs longer to bring the temp back up? Is this correct? If my house is fairly tight, new boiler, is their a swing seting that is most common/best to set at? Thanks, Bill
 
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Old 09-20-08, 08:30 PM
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Which model thermostat Bill ?

Are you sure that's not the CPH (cycles per hour) setting you are looking at ?
 
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Old 09-21-08, 02:02 AM
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It's comfort vs mechanical efficiency. If it's a conventional boiler I would guess you'd strive for about a 10 minute burn or more if you can. You can probably play around with it and get a better answer than us here guessing. Experiment time...
 
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Old 09-21-08, 05:15 AM
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understanding temp swing settings/thermostay?

...thanks guys! Its an Lux TX9000. They call it the swing cycles!, but the boiler would cycle on??? Bill
 
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Old 09-21-08, 08:16 AM
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The instructions for the older (discontinued) 9000 say that a setting of 4 is appx +/- 1F. I would start there...

I would imagine that in an older, leakier, draftier home, a higher setting might be beneficial to the boiler, not allowing it to fire as often, but at the expense of comfort.

Instructions go on to say that the boiler should be firing 3-6 times per hour ... 6 seems high to me ... I would be OK with 3 ...

But basically, that setting affect the 'differential' the t'stat operates on. Or, maybe more rightly called, the amount of 'hysterisis' that it uses. Lower settings would mean that the room has to change temp LESS before the boiler fires, but may start short cycling the system. Higher settings would mean larger swings in temp, but boiler would fire less often.

Yes, experiment... find a comfortable compromise between comfort and boiler cycles.
 
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Old 09-22-08, 06:22 PM
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Is one of these options more efficent- in other words- is it more fuel efficent to maintain a steady house temp, or to cycle and have the temp vary 5-8 degrees when your home. Also, I was once told that by turning down your thermostat too far, you almost wasting fuel having the furnace try to heat up again evry day.. but that never made sence to me...
 
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Old 09-22-08, 07:11 PM
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Almost everyone believes that turning the t'stat down will save some fuel. It has to, right ? Ummmm.... I'm not sold on that myself, and what follows is mostly opinion, based on personal observation.

I tend to agree that whatever you've managed to save by setting back is pretty much gonna get eaten up by the recovery. There are some caveats though...

In a home with scorched hot air heating, since the recovery time seems to be faster than a home with hydronic heat, there _may_ be some savings to be had by setting back. I don't have scorched air heat, so can't do any measurements.

I have to believe that LONG periods of setback, i.e. weeks or even days, _might_ save a percent or three over the long run. You HAVE to save by running a lower temp inside. The heat loss is less with less temp difference between indoor and outdoor.

Let's say you drive yer car on a long trip... and set the cruise control at a moderate setting ... you will save fuel by not speeding and being consistent with your speed. Throw a few 'jackrabbit' starts in there, off from a traffic light trying to beat out that sports car in the next lane, and there go your savings. same same ...

I don't believe that any 'significant' savings can be had by setting the temp way back for 6-8 hours, then up for a few hours. This is where the savings is gonna get eaten up by the recovery. I have taken significant data to prove it to myself that this is true in MY home, with MY lifestyle. Your results may differ.

I DO set my t'stat back at night by a few degrees, for sleeping comfort only. It's all about the comfort. If you are comfortable wearing a sweater and wooly socks, then set your t'stat at 62 24/7 ... you WILL save fuel. My opinion is that jackin it up and down won't save a thing ...

As for efficiency versus length of burner run time ... the longer the burner runs, the more efficient it is. If you had a modulating system where the burner ran 100% of the time, matching it's output to the heat loss of the home, you would have maximum efficiency from that burner. If one could live comfortably with a few degrees of temp swing in the home, it would probably save a bit of fuel by having the burner off for longer periods of time, but running a bit longer when it did run...
 

Last edited by NJT; 09-22-08 at 07:32 PM.
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Old 09-23-08, 05:01 PM
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I am going to throw my 2 cents worth at this. I believe when stats are given on this subject along with anything else in the heating industry it is assuming all is well. As we know 90% of all heating appliances are oversized by 50 - 100% or more which kinda spoils the milk here. If the appliance is oversized it will short cycle and cause the efficiency to drop and use more fuel. If the boiler is properly sized it will give you longer run times and keep an efficient operation. If you have OD reset it would take forever to recover.
I would think there are limitations to how far and how long. I always heard a minimum of 8 hours and a maximum of 5 degrees. Don't know if that holds water or not. I agree with Trooper I do it for sleep comfort.
 
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