Correct high and low limit temp on hydronic system

Josh_17

I have a 4 section oil fired Peerlees hot water boiler. The system has 2 zones and is connected to a 45 gal indirect water heater. I have the hi/low temp set at 180/160 on the boiler and 160 on the indirect(which I mix down to 140). Are these the most efficient settings for the boiler and indirect?

Thanks

Joel M

That is fine as long as you are getting good heat. If not, you may want to go higher.

Derheatmeister

Why is the low temp set to 160 vs 140 ?.. if you set it to 140 then you boiler will not condense and maybe will cycle less, which may result into better fuel savings.

Joel M

We have winter temps down to zero and below. I dont think 140 degree water would be sufficient to heat the home.

Derheatmeister

Why not? Maybe you should try it! We have -15 F and lots of systems that are set for 140/180.I guess it all goes back to proper Design Work i.e. lin foot of heat emitters Per heatloss of the Room. A short cycling boiler is kinda like stop and go traffic .But then again if you are not emitting any heat doe to low temps (improper heat emitter sizing ) then you are spinning you tires to. HM.

Josh_17

Correct high and low limit temp on hydronic system

What would constitute short cycling. I am not opposed to trying it, only concerned that by allowing the temp to drop to 140, it will keep the boiler on longer to get back to 180, using more oil. I am also concerned about what it will do to hot water output from my indirect.

tk_3

Remember the low setting does not determine your heating water. The boiler on a call for heat will run to high limit. A setting of 160/140 will allow the boiler to go to 160 on a call for heat. I would suggest 140/180 and a differential setting of 25.

Weezbo

there is something to this question

works somewhat like this, the designed water temp for the system is say X ,....the greatest part of the heating season it will never get to that temp X... at that time ,ideally you would want the boiler running constantly with an internal temp

within your home of say 70 F ....

so, depending upon the requirements of the equipment heat source ( you have to take into account lowest sustainable return fluid temps, for an example another might be design of the stack and its temp requirements for proper combustion) and your definition of financial comfort ,you have choices to make.

thats about as clear as i can get

*~/:)

Bob Bona_4

crank

that low limit down! If you have an indirect, and it's wired right, it's call will rev up the boiler to the high limit. Maintaining a low limit of 160 is defeating the purpose of having the indirect-to save fuel. 180 is the "typical" high setting for decent indirect recovery. You should look into outdoor reset for even better energy savings.

bill nye_3

Josh

"it will keep the boiler on longer to get back to 180, using more oil. I am also concerned about what it will do to hot water output from my indirect."

No, you are going to use more oil to maintain the higher standby temperature. As long as you have a minimum of 20°difference between the hi and lo you can do whatever you want.

The call for heat may be satisfied before the boiler gets to high limit, that's a good thing. The real point is , it's gonna take what it's gonna take to heat the house. The best way to save is to tighten up the house. You are really just trying to replace the heat that is lost to the outside.

On a near 0° day my boiler temp. may get to 165°. Most of the time it is 120-140° or less.

This stop light grand prix, on-off boiler operation is like driving with your foot to the floor board all the time. You "might" need the 180° about three or four days a year.

For every 3° F you can lower your high limit you are supposed to save 1% of your heating cost.


Most residential boilers, modern ones, can get up to high limit in a few minutes. I think you would save more by reducing the standby loss and reducing the low setting.


With an indirect, I would try 130/170°

Derheatmeister

Science Guy, Do not forget that this boiler is not a Condenser!!Hence,well depending on altitude , A Lower setting than 140 F will cause Flue Gas Condensation!! I have seen Boilers deteriorate after a few Years!!.

bill nye_3

DerHeatmeister

How long you figure that boiler is going to stay below 140° ? On a call for heat it is going to go to Hi limit.

I have seen apartment buildings with black pipe and iron radiators w/six pumps all wired with RA89's. Now that will condense. But you take an average house with the pumps wired through ZC/ZR on the aquastat and it just not going to happen. Well, unless you turn the house down to 50 and come home and jack it up to 80 everyday.

I do have have a Viessmann Vitola at home so I guess the 120° stuff wouldn't apply here. But any 368,468, GO3,GO4, V74, V84, etc is going to get above dew point in 2 or 3 minutes. Especially when zones have less than 40' of baseboard on them sometimes.

So you got a house with four or five zones, how big can the zones be?

Derheatmeister

Yes,maybe i am comparing some of the bigger systems that we work on up here in the rockies(14000Sqft and Radiant).and this system was only a 2 zoner maybe 1400sqft?? and baseboard.Which will mostly emmitt approx 550 btu/lin Foot @180F . If this system is to be more eff ( and I can't really judge it from here)and it is Short cycling maybe depending on it's age it's time for a "Control or a buffer tank? ,Or a Condensing boiler? Maybe the boiler is over sized? to many things that we do not know yet!!