Typical boiler temperature, pressure, etc? Educate Me

HandyFS

I'm just getting a Weil Mclain boiler back up and running which sat dormant for about a year or so. I have no history of how the system ran other than its past settings. I've had air fired furnaces all my life, so I'm just trying to better understand this boiler system, and what to expect.

Hoping you can all help me understand some general common stats and facts when running a residential boiler system. Things like typical temperatures, pressure, etc.

I'm running a Weil Mclain WGO-5 oil fired boiler with 2 zones and cast iron radiators with a few under-window convection radiators.

Pressure (Cold vs Hot):
What is common pressure in a residential boiler system when cold/warm? The manual states 12 psig is recommended cold pressure (With a maximum of 50 psig during pressure testing). Assuming I will stick to 12psi cold based on that. What should I expect that pressure to reach once its warmed up, about double?


Temperature and Limits:
The manual doesn't mention anything about common running water temperature other than that its max temperature is 220°F. Based on the old Honeywell aqua stat (L8148 which seems to have a temp rating of minimum 180°F to 240°F), its settings seem like its set to 180°F with a high limit of 195-200°F based on where the dial sits. What is common temperature to run a system? I've seem many mention 160°F, some say 180°F, and then others all over the place saying they are running lower in the 120's, and I've seen some say higher. I'm assuming temperature required to heat the house will vary and that's why there is so much variation. Just looking for some general numbers and a guide. Since it was set at 180°F I'm guessing this is what it takes to heat the place, but I'd be interested to hear some feedback if this is common, high, etc.

Based on the Honeywell L8148 aqua stat, I'm guessing the system is set at 180F as its default and that's where its been all its life.

Typical temperature swings and starting/stopping of burner
The system seems to run and heat to about 180°F-185°F before it cuts off. As the zones are still calling for heat the circulator pumps run and once the temp drops to about 170°F, the system will run again and bring it back up to 180°F. If no calls for heat the system naturally will not run and won't fire until a zone calls again. Assuming this is is common function? From what I understand this aquastat controller only has a high limit (And max limit) and not a low limit, so there's no way to control how low it drops until it kicks back on.

So it runs to its 180°F setting as the aquastat is set, and then the system lays dormant until about 170F when it kicks back on. Unsure where this 10 degree difference setting is that then has the system fire back up, is this a default of how the aquastat functions since it has no low temp setting?

Is there reason to update the aquastat to gain the ability to set the low level so the machine won't fire as soon, or something like that? I don't have experience or fully know if there is benefit to this or not, so I'm trying to better understand.

All knowledge shared appreciated!

Jamie Hall

You're observations make it sound to me like it's running pretty well at the moment. Might need some tuning...

On pressure -- 12 psig cold is typical. When it's fully hot, it might run up to as much as 18 to maybe 20, but shouldn't get much over that. If it does, the expansion tank may need attention.

The temperarures you are seeing are normal (the 180 cutout to 170 cutin is the differential -- some aquastats it is adjustable, some not). You may find you can run a lower temperature, but likely that will do just fine. The idea is whatever works to heat the house!

Don't be tempted to put a fancy thermostat on. Setbacks more than a few degrees don't work well with hot water, nor do frequent setbacks.

HandyFS

Jamie Hall said:

You're observations make it sound to me like it's running pretty well at the moment. Might need some tuning...

On pressure -- 12 psig cold is typical. When it's fully hot, it might run up to as much as 18 to maybe 20, but shouldn't get much over that. If it does, the expansion tank may need attention.

The temperarures you are seeing are normal (the 180 cutout to 170 cutin is the differential -- some aquastats it is adjustable, some not). You may find you can run a lower temperature, but likely that will do just fine. The idea is whatever works to heat the house!

Don't be tempted to put a fancy thermostat on. Setbacks more than a few degrees don't work well with hot water, nor do frequent setbacks.

Thanks for the info. So it sounds like things are running as expected, that's good to hear. With a fancy thermostat, do you mean something like a Nest that learns and tries to predict its own settings? I was planning for just typical day programmable thermostats on this system, or if its a smart thermostat so it can be controlled remotely, it won't be using predictive changes and will stay on the set schedule.

Jamie Hall

The typica 5-2 or 7 day programmable, battery powered, will do everything you need it to do. Installing a smart thermostat can be a real hassle, and for why?

EdTheHeaterMan

Let me say this about your oil burner and control system. The L8148 that is standard equipment on your Weil McLain is usually factory set at 180° high limit. That control does not have an adjustable differential. It is factory set a 10°. Since you have Cast Iron radiators in your home, you may be able to save a small percentage on operating cost by lowering the high limit to 170° or 165°. That is because most of those old radiator systems were oversized and will work nicely at lower water temperatures.

If you choose to lower the limit to say 165ish, and you discover that on extreme cold weather your heater does not make the it to the thermostat set-point, then all you need to do is put it back to 180°. If however you find that when it is in the really low temperatures outside and the Weil Mclain keeps you comfortable at 165° in the radiators, then you will be saving on oil for the remainder of the time you live there with that boiler.

And regarding those smart thermostats, I have always had one in my old home, and when ever I went on a vacation for several days, I'd said to myself... "Self, when we return from this vacation, don't forget to go on the internet and turn on the heat or air conditioner when we start to drive home from the airport or hotel or wherever". You know what... Never happened.

Tools are only as good as the user. What does that say about me?

Mr. Ed

mattmia2

My setback thermostat has a hold of x days until x time of day setpoint. Can make it resume the schedule before you get home.

HandyFS

EdTheHeaterMan said:

Let me say this about your oil burner and control system. The L8148 that is standard equipment on your Weil McLain is usually factory set at 180° high limit. That control does not have an adjustable differential. It is factory set a 10°. Since you have Cast Iron radiators in your home, you may be able to save a small percentage on operating cost by lowering the high limit to 170° or 165°. That is because most of those old radiator systems were oversized and will work nicely at lower water temperatures.

If you choose to lower the limit to say 165ish, and you discover that on extreme cold weather your heater does not make the it to the thermostat set-point, then all you need to do is put it back to 180°. If however you find that when it is in the really low temperatures outside and the Weil Mclain keeps you comfortable at 165° in the radiators, then you will be saving on oil for the remainder of the time you live there with that boiler.

And regarding those smart thermostats, I have always had one in my old home, and when ever I went on a vacation for several days, I'd said to myself... "Self, when we return from this vacation, don't forget to go on the internet and turn on the heat or air conditioner when we start to drive home from the airport or hotel or wherever". You know what... Never happened.

Tools are only as good as the user. What does that say about me?

Mr. Ed

Thanks for breaking that all down for me, Ed. What you mentioned about running at 165 is what I have seen people mention so I'm glad you broke that down for me. So with the L8148, I'm assuming if I wanted to take a chance at lowering it down to 165, I would need to install a new controller that gives that lower level temperature setting capability? I could be wrong but I saw there were 2 models, and one had a temp limit of 180-240, and I think that's the one I have, so 180 is the minimum this controller can go.

The machine is the Weil Mclain WGO-5 which has a hefty GPH head it in (1.45 GPH if I remember correctly) versus the 1 gallon or less my forced air furnaces have run over the years, so the idea of saving some oil is appealing but I may hold out and let the machine run this season as is and then consider upgrades or changes next season.

I'm currently working on trying to get replacement radiators so I can see how the entire house does once its running as it was designed. Steps and stages, I'm getting there slowly.

Jamie Hall

On the oil usage -- that is determined by the overall efficiency of the system. The flow rate of the nozzle actually has very little to do with it, since it is likely that the burner isn't firing all the time. Patience.

hot_rod

Short and frequent boiler cycles will drive down efficiency and fuel consumption up

Ideally you would do a heat load, match the radiators and boiler to that

if you have more boiler then radiators you may experience short cycling

a 10 minute or longer burn cycle, and on design days the boiler would run non stop if everything was sized accurately 

Dave Carpentier

It probably goes without saying... but use caution under that lid, there is 120v on that control.

EdTheHeaterMan

So with the L8148, I'm assuming if I wanted to take a chance at lowering it down to 165, I would need to install a new controller that gives that lower level temperature setting capability?

Not at all. If the L8148 you currently have, has the adjustment stop where it will not let you go lower than 180°, then all you need to do is adjust the "Stop Arm". The instructions and illustration to the left of the photo of the control tells you how to do it.

And Yes... @Dave Carpentier is correct. there is 120 VAC in the box, so turn the switch to the boiler OFF before working on that control.

HandyFS

Jamie Hall said:

On the oil usage -- that is determined by the overall efficiency of the system. The flow rate of the nozzle actually has very little to do with it, since it is likely that the burner isn't firing all the time. Patience.

Didn't think of that, great point. I guess the true test will be see how the machine does once the system is in full use and time passes.

hot_rod said:

Short and frequent boiler cycles will drive down efficiency and fuel consumption up

Ideally you would do a heat load, match the radiators and boiler to that

if you have more boiler then radiators you may experience short cycling

a 10 minute or longer burn cycle, and on design days the boiler would run non stop if everything was sized accurately 

Interesting stuff. This house is all new to me, so I'm going to find out how it all goes. Eventually I may replace this system, but hoping it does the job for a few years as is.

Dave Carpentier said:

It probably goes without saying... but use caution under that lid, there is 120v on that control.

Thanks for the reminder!

EdTheHeaterMan said:

So with the L8148, I'm assuming if I wanted to take a chance at lowering it down to 165, I would need to install a new controller that gives that lower level temperature setting capability?

Not at all. If the L8148 you currently have, has the adjustment stop where it will not let you go lower than 180°, then all you need to do is adjust the "Stop Arm". The instructions and illustration to the left of the photo of the control tells you how to do it.

And Yes... @Dave Carpentier is correct. there is 120 VAC in the box, so turn the switch to the boiler OFF before working on that control.

I could be off, but it seems that there are different versions of the L8148 out there, some that allow lower minimum temps (I see some have 140F as the minimum on the dial), but the one I have seems to have 180F as the minimum on the dial, and goes up to 240F. So if that's the case I guess I'm stuck at 180F as the minimum possibly with this particular model?

Thanks everyone!

EdTheHeaterMan

I could be off, but it seems that there are different versions of the L8148 out there, some that allow lower minimum temps (I see some have 140F as the minimum on the dial), but the one I have seems to have 180F as the minimum on the dial, and goes up to 240F. So if that's the case I guess I'm stuck at 180F as the minimum possibly with this particular model?

That would involve purchasing a new control.
My idea of moving the stop lever only involves purchasing a screw driver, if you don't already own one. ...and that screw drivers can be used on other thing like, say, driving and removing screws.

So, what I am saying is to rotate the dial until you reach the lowest temperature, then pry the stop up and rotate the dial a little more. Make believe there are lower numbers on the dial. The L8148 does not read the numbers. It's not that smart. It is analogue. That dial just increases or reduces the pressure on a spring based on the direction you turn it.

I know, it sounds like cheating... But if you don't tell, I won't tell

HandyFS

EdTheHeaterMan said:

I could be off, but it seems that there are different versions of the L8148 out there, some that allow lower minimum temps (I see some have 140F as the minimum on the dial), but the one I have seems to have 180F as the minimum on the dial, and goes up to 240F. So if that's the case I guess I'm stuck at 180F as the minimum possibly with this particular model?

That would involve purchasing a new control.
My idea of moving the stop lever only involves purchasing a screw driver, if you don't already own one. ...and that screw drivers can be used on other thing like, say, driving and removing screws.

So, what I am saying is to rotate the dial until you reach the lowest temperature, then pry the stop up and rotate the dial a little more. Make believe there are lower numbers on the dial. The L8148 does not read the numbers. It's not that smart. It is analogue. That dial just increases or reduces the pressure on a spring based on the direction you turn it.

I know, it sounds like cheating... But if you don't tell, I won't tell

Thanks for the tip, I thought I was stuck based on the minimum but its good to know it can possibly do the temp drop without needing new components. If I find the time to give it a try I'll be sure to share an update on how I make out.