Triple Aquastat

Kevin_54

I was just reading the Hot Water Handbook from Firedragon and it says that internal tankless heater ratings are based on an internal boiler temperature of 200 degrees. Keeping this in mind, what would the proper HI-Low-Diff settings for the Triple Aquastat be?

Al Letellier_9

triple aquastat settings

It depends....on the size of the system, the temperature needed to satisfy the heating and hot water demands, but typically, 200 High/ 180 low with differential at 20-25. That is the typical setting here in the north country (Maine). You may get away with lower settings but keep the h/l at least 20* apart. The higher diff. settings will allow the boiler to run longer to a higher setting for domestic calls and give a longer drawn down to the low limit

Glenn Sossin_2

It's in the numbers

The hotter the water, the higher the recovery rates or capacity ratings of exchanger type products. All the manufactures play this game.

Realistically, no one sets the controls that high - it burns a tremendous amount of fuel. Creates excessive wear and tear on your heating system components - accelerating their demise. Actually, I've come across some unscrupulous oil techs who will set the temps way up there. It burns more oil, thats how they make their money.

Normally these controls are set between 130 and 160F - higher in the North Country. When your coil starts to fade consider an indirect like a Phase III .

Unknown

130 is too low

for a triple aquastat on a boiler with a coil . I was back yesterday on a recent install that had a triple and coil . Complaint was not enough hot water . Found the settings at 185 HI - 150 LO - DIFF 10 . I forget how the DIFF affects the low setting , but I do know 150 will give you a cold shower pretty quick ( I had a coil boiler for decades and used to experiment with the settings in summer . )

We reset the aquastat to 195 - 180 .

Glenn Sossin_2

too high

Your coil is probably old and scaled up. Thats why you have to set it so high. I agree 130 is on the low side but with a small differential, and a new boiler install, I think you would get enough heat for the typical shower.

Also keep in mind, these controls are mechanical in nature so the what ever setting you dial can be off by up to 10F or more.

Glenn Sossin_2

differential function

I believe it works like this.
The differential, as it applies to the low limit, determines the range at which the boiler fires and disconnects the circulator circuit.

In the example you gave, the boiler would cycle on and off between 140 (150 low limit less differential) and 150 assuming there is no heating call. When the water temp would drop below the 140 number, the circulator would not function allowing the boilers heat energy to be directed towards making hot water.

If you had a differential of 20, the boiler would cycle between 130 (150 - 20) and 150.

On the high limit side, on a continual heat call, the boiler will cycle betweent the high limit setting or 195 and 185. IF the differential was 20 - it would cycle between 195 and 175.

Read page 10 of the attachment on this control.

Unknown

Actually

the boiler and coil were 2 weeks old . It seemed like the triple aquastat didn't react fast enough to keep the water hot with the low setting at 150 .

Probably 3 of 4 of our accounts use a coil for hot water . I've installed a few thousand coil boilers in my work lifetime . I might not know much in life , but coil boilers I do know . Even with brand new equipment I would not set the aquastat as low as 130 , not even 150 . They just don't produce enough hot water at that low a temperature . We are talking about properly sized boilers ? Because I'm pretty sure a boiler oversized by 2 times might work well with that lower temp . Not trying to get in a pissin' match with ya Glenn , just my humble , somewhat educated opinion .

Unknown

Thanks for the link

That low limit function always messed me up . So what happens I think is the burner will always come on after a drop of 10 degrees of the low limit setting ( no call for heat ) ? No matter what the DIFF is ? And it will run to the actual low setting unless the DIFF is higher than 10 ? If the DIFF was 15 the burner would run to 5 degree higher than the low setting ?

Unknown

L8124 Settings

I'm going to have to disagree with you on most of these points Glenn. The High and Low limits normally would be set 20°F or so apart and the differential for 20-25°F. The adjustable differential setting has absolutely nothing to do with the High Limit setting. It determines how high the boiler water temperature will rise from the Low Limit's fixed 10°F differential when there is no call for heat. Here is how everything works.

When there is no call for heat the boiler will maintain a minimum temperature for the coil using the Low Limit setting. There is a fixed internal differential so that when the boiler water drops 10°F below the Low Limit setting the burner will fire. The burner will stay on and heat the water up to a point determined by the Adjustable Differential setting you set at which point it will shut off and the cool down cycle will begin again.

When a call for heat is encountered, the burner will turn on and raise the water temperature to the High Limit setting and the circulator will operate. The High Limit also has a fixed internal differential of 10°F so when the water cools down 10°F from the High Limit setting the burner will once again fire and raise the water back up to the High Limit setting. If while this is happening, the boiler water temperature continues to drop to 10°F below the Low Limit setting, the Circulator will be denergized until the water temperature has risen to the Low Limit Setting again.

As an example let's look at a boiler with settings of High Limit of 190°F, Low Limit of 170°F and Differential of 25°F. When there is no call for heat the boiler will cool down until it reaches a point 10°F below the Low Limit or 160°F, the burner will fire and the temperature will rise by the Differential Setting of 25°F until the temperature of 185°F is reached or 160°F + 25°F, at which point the burner shuts off. This will keep cycling like this until a call for heat is encountered. When that happens, if the temperature is 10°F cooler or lower than the High Limit setting the burner will fire and stay on until the High Limit setting of 190°F is reached. The burner will shut off and stay off until the temperature drops 10°F below the High Limit or 180°F. If the water continues to drop to 160°F because someone is in the shower, then the circulator will shut off until the temperature rises back up to at least the Low Limit setting again. This function is to help establish priority for the poor soul that is starting to feel the cold shower.

The settings you suggested are not even close to being conducive to Domestic Water production and you will have the boiler operating below its dew point a good amount of time. In addition to that that poor soul in the shower won't be in there very long! Look at this graphic and you will better understand the functionality of the control.

Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.

Glenn Sossin_2

I stand corrected

I stand corrected on the differential functions. I looked up this graphic that you posted in my old spec sheets. I was wrong, you are cleary 100% correct.

It's been my "limited" experience that during the summer I typically find them set at 140 - 160, then they are raised higher, 160 -180 or higher for the winter season.

Recently, with the cost of oil virtually doubling, you find alot of homeowners, particulalry low income or eldery on fixed budgets struggling with the bills. Unforunately, these are typically the very people that have the coil installations. I have suggested/turned these settings down that low to save oil. 130 is the lowest I've ever set a low limit to. Never heard back a complaint. Thats what I based my response on.

The flue gas condensation is an excellent point that I didn't consider -will change my ways. I don't mind being corrected - if I'm wrong.
Thanks

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