Differential Setting ?

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  #1  
Old 01-17-09, 08:44 AM
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Differential Setting ?

With the onset of this nasty cold weather it seems like my system will keep the house at the current temp but won't go up.

Hi limit 180
Low limit 165
Differential 15

Should I raise my limits up or lower the differential to 10 or 5 on these frigid days ?

Thanks
 
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Old 01-17-09, 09:09 AM
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Hi Dogs...

The HIGH setting controls the high limit for heating the home.

The LOW and DIFF settings control ONLY the 'keep warm' of the boiler. Presumably since you have a 'triple' aquastat, you've also got a 'tankless' coil in your boiler which provides domestic hot water, correct? If you do NOT use the boiler for hot water, you can back that LOW setting down and save some fuel.

The setting you have now, your circulator pump may not run until the boiler reaches 165...

It's not generally recommended to set the HIGH and LOW closer than 20... which you've only got 15 ... setting too close can interfere with proper circulator operation. I would back the LOW down to 160, and either leave the DIFF at 15 or INCREASE it to 20. Lowering the DIFF will give shorter cycling which you DON'T want.

As long as the system can maintain the setpoint on the t'stat, you don't need to do anything with the HIGH setting. If you feel the boiler is having a real hard time heating the home, you can temporarily increase the HIGH setting a bit... I wouldn't go over 190 though... but as I said, as long as it can MAINTAIN, you're OK.
 
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Old 01-17-09, 11:04 AM
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Yes, a triple is what I have. I just changed the diff to 20, and raised the high to 190, after looking on the inside of the cover of the stat, I noticed I put a sticker for these cold days to kick it up to 190. (guess, it must have happened to me before, just don't remember when)

The cold snap in the Pocono's is one of the most brutal in years. Glad these below ZERO, and single digits will mostly be over after tonight for a couple days. (would like the rest of the year to not get below 32)

One more question .. Why not a shorter cycle time? Wouldn't that get the boiler keeping the water hot so it would heat the inside a little easier?


Thanks...
 

Last edited by 2dogs2; 01-17-09 at 11:17 AM. Reason: One more question on same topic
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Old 01-17-09, 01:27 PM
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Shorter cycle times are harder on the equipment. Shorter cycles means MORE cycles. It's the startups that are hardest on stuff. Also, it takes some time for the burner to reach 'steady state' where it is most efficient, short cycles sometimes never let the burner get there. So, from an equipment point of view, it's harder on it, and from an efficiency point of view, longer cycles are better.

Remember that that LOW and DIFF setting have nothing really to do with heating the HOME. All they do is keep the boiler hot so that you have domestic hot water. If you weren't using the boiler for domestic water, you could theoretically let it go COLD in between heat calls.

ARE you using it for domestic water? If not, you can save a ton of fuel by turning the LOW way down...

And, 165 is pretty hot for domestic hot water... do you have a tempering valve on it?
 
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