Honeywell Aquastat Question

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Old 01-21-08, 09:56 AM
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Honeywell Aquastat Question

Hi,

I have a question about the diff setting, Can I increase effeciency by increasing the diff range? If it provides too much hot water at 10 can I try increasing to 15 or 20 and if that works will it make a difference in saving oil? Or does the opposite help?


Thanks!
 

Last edited by happyowner98; 01-21-08 at 10:47 AM.
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Old 01-21-08, 10:50 AM
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We set most boilers at 160oF on 180oF off
Id say more this way---- When was the boiler cleaned out good. When was the oil burner cleaned nozzle filter all new . Burner checked draft set .checked Co2?????. This is where you save on oil.
 
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Old 01-21-08, 12:12 PM
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Hi Ed,

I bought the house in July and I had the burner serviced by the oil company that I "inherited" with the house in September, we have a warranty on the burner with them. The tech cleaned, and ran co2 tests and everything read fine. Our house is cold and drafty poor insulation and heater ran alot. When I checked the aquastat recently I noticed it was set Hi = 160 low = 140 and diff = 10. After reading I am setting Hi to 180 and leaving the low alone because there is actually too much hot water supply etc. Does this make sense, Do you think i can set the diff higher and save?

Funny you mention the draft because mine gets stuck and I hadn't thought too much of it.
 
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Old 01-21-08, 12:26 PM
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[QUOTE][Funny you mention the draft because mine gets stuck and I hadn't thought too much of it./QUOTE]
Make sure you fix it. That barometic damper is a big part in how the burner burns and if the flue pulls to much heat out of the boiler on you.
 
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Old 01-21-08, 12:37 PM
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Do you have any suggestions?

The draft works most of the time, but sometimes when I'm downstairs I notice it hasn't opened when the flue is in use. My temp fix was to put some tape on the opening for the "tab" on the hinge so that it does not quite swing all the way closed when it is off, so it doesn't get stuck closed. I will take a look at it tonight and see if it is functioning proper.

I hope we are on the same page, I am talking about the flap on the flue. I am pretty sure the settings for when the flue is in use and not were all ok when checked.


How about that diff setting question? Does it really make that little difference?

Thanks!
 
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Old 01-21-08, 01:33 PM
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The diff on your control tells the burner how long to run when it fires on Low setting. The control drops 10f (built in) then burner fires and will run until the diff is added to the low side-10f. Example;
160 low and 180 high diff 10f. The burner fires up at low -10 (built in) 160-10 = 150. Burner on. It will heat up the amount the differential is set, so it will shut off at 160f. 150f + 10 (diff). This is short cycling and short cycling wastes fuel. Now let's expand the diff to 20. Same settings on high and low. Now 160 (low) - 10 (built in) burner fires. Now it runs to 170f with a diff set to 20f. Low - 10 + diff = 160 - 10 + 20. Longer cycles equate to higher efficiencies. Set the diff on this type of control all the way up. Longer run and off times.
 

Last edited by NJT; 01-21-08 at 03:30 PM. Reason: corrected math
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Old 01-21-08, 02:47 PM
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OK I want to try and save some by keeping the heat down a little from 180 lets say hi is set to 170. Does it make sense to drop my low to 140 to widen the gap? I understand that it will burn again at 160 (Hi-10) during call for heat on this setting. but say there is no call for heat for a while and it just keeps dropping to 130 and then burns to 155. Am I saving there or will I waste fuel on a call to heat burning all the way back up to 170? (would it be better to set the low at 150 with the hi at 170 and shorten gap)

Does anyone see what I'm trying to get at? Does this make better sense in summer months? Does it not matter at all in Winter when there is a persistent call for heat?
 
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Old 01-21-08, 03:46 PM
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It's kind of a toss up whether changing the high setting will save anything really. With cooler water, the boiler may have to run a little bit longer to transport the heat (via the water) into the home. So what you save by lowering the temp may be lost by running a little longer (on average).

The HIGH and LOW settings are independent of each other.

The HIGH setting controls the space heating, the adjustable DIFF has nothing at all to do with that setting. It's FIXED at (usually) -10 . So, if you get a call for heat, the burner will fire until it hits the HIGH limit, the circ will continue to run until the water temp cools to 10 below the HIGH setting, at which point the burner will fire again. This is assuming the thermostat hasn't been satisfied during the heat call. If the t'stat satisfies, the burner and circ will shut down.

The LOW setting controls the "KEEP WARM" settings, for heating your domestic water. The DIFF only acts on this setting. If you have adequate hot water at 140 on the LOW, then leave it there. If you set to 140 with the DIFF at 20, the 'keep warm' will cycle the boiler between 130 and 150 . rbeck is recommending max out the DIFF for the longest burn cycle, this will be the most efficient.

If you find that you still have adequate hot water at 130 on the LOW setting, then by all means, go for it. But leave the DIFF at 20 .

Is there a "MIXING VALVE" on the hot water coil ? If so, is it set to 120 (it should be). If you do have a mixing valve to temper the hot water to the house, you don't want to decrease the LOW setting below 130 as now, the water will drop below the temp of the mixing valve.

You won't save much if anything at all by 'messing' with the settings. Personally, I would set it at 180 HIGH, 140 LOW, 20 DIFF. Then I would go and buy some rolls of insulation, and shrink wrap for the windows, and caulking to seal any gaps. The money you save on those steps will be FAR outweighed by anything you do to the aquastat settings. There are no 'magic' settings !
 
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Old 01-22-08, 09:39 AM
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thanks trooper, that helped!

I set the high to btween 165* and 170* after watching a few cycles and noticing that on this temp the boiler breaks at about 175* but heats to around 180*. (I also noticed that at this temp it starts burning at about 160* and then it dips to 150* for a bit) so it seems to have a 30* range when there is a call for heat. Which I hadn't anticipated when trying to do all the math yesterday.

When things warm up I'm going to try to remember to check that my lo 140* setting actually starts burning at 130* because of the discrepancy in the range of the hi. I don't want to set it back like the hi now because I can't observe it.

I set the diff all the way up to 25* and plenty of heat in the shower so OK.

I got rolls of fibre, need to get smore. and I also have the frost king kits for my windows. this summer I'm going to invest in storm windows.

I think I might also consult an insulation contractor soon.

Thanks for all the help!
 
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Old 01-22-08, 03:32 PM
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I wouldn't count on absolute accuracy of either the aquastat setting, or the temp gauge on the boiler. Ballpark is fine though, as long as it's within say 10% ... won't really make much difference. Problems come when the aquastat is off in one direction and the temp gauge is off in the other.

You might be seeing 'heat soak' when the temps climb after the burner cuts off. There's still a lot of heat trapped in that cast iron that continues to transfer to the water after the burner cuts off. Don't be surprised or alarmed if you see the temps occasionally climb above 200 even. This could happen if there's a heat call that is satisfied at the same time the burner cuts off. Since the thermostat is satisfied, the circulator will stop running also. Now that heat in the cast iron is going to continue to heat the water in the boiler, and no water will be coming back to the boiler since the circ is shut down ... that's normal operation.

You are correct that the LOW and DIFF settings are more important during the summer months, because during heating season, it's likely that the boiler will be hot ANYWAY because of heat calls...

Good Luck!
 
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Old 01-23-08, 12:01 PM
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Thanks again,

I feel really comfortable with how this works now. It's real nice to know some about it because I come from a house with electric heat all my life.
 
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