Old Weil, gravity system, no bypass valve/piping installed?

iridium

I am currently renting a house with Weil McLain CGM-5 series 6 boiler from the 1980's. The system consists of heavy cast iron radiators. I do not see a bypass valve or piping set up to protect the boiler from low return water temperatures as it heats up.

It just ran for a 40 minute cycle from cold (last time it was on was ~4 hours prior). At the end of the 40 min cycle the outlet temperature only reached ~130F. Return temperature ~110F. There's so much mass in this system it takes forever to warm up.

Of note I did replace the old honeywell thermostat on the wall with an ecobee. Its a simple 2 wire hookup for heat... on/off. I only had the original honeywell running the heat for a short time earlier this year. It would seem to short cycle sometimes, but I never looked at water temps at that time. I don't think it had any additional smarts to it.

I'm confused how this boiler could have lasted so long with low return temps for extended periods of time?

Did the old thermostat protect the system somehow by design or accident?

gyrfalcon

How are you measuring the temperatures?

iridium

A cheap IR thermometer. There is also a combination pressure/temperature gauge on the lefthand side of the unit which appears to read supply or boiler temperature.

Here's a manual for series 6. Oddly it doesn't list CGM-5 as a size. The gauge I am talking about is item 4 on page 7.
https://www.weil-mclain.com/sites/default/files/field-file/cgm-pcg-series-6-manual_1.pdf

Based on serial number this unit was manufactured in 1979.

With my ecobee the boiler doesn't run very often to maintain set point temperature (65 when home, 63 sleep, 60 away). Threshold temperature is set to 1.5F so it kicks on when 1.5F below setpoint. I was thinking lowering the threshold would make it kick on more often and maybe keep the temperature up? Runtime would be shorter then though so maybe that wouldn't really help.

A typical run time right now seems to be 45-75 minutes 2-3 times a day when called for heat. Outside temperatures are in the range of 50F day and 35F night this week.

Jamie Hall

Basically you want as long a run time as you can with those things. Make sure you do that; I seem to recall the Ecobee has an option to set one cycle per hour (the old Honeywell had an anticipator, which worked better if it was properly set).

It's a funny thing about those old time massive teakettles. Condensation just didn't bother them much -- too much iron -- unlike the new tinplate ones.

And no, you can't put a bypass valve on a gravity circulation system. No pump.

gyrfalcon

When measuring with IR gun, beam at black or other matte/ painted metals, bare copper will give inaccurate reading.  

pedmec

The long run cycle is drying out the cast iron. Your most like only getting condensation on start-up but eventually when it reaches steady state and the flue gas starts to increase in temperature above the dew and it will dry it out. Not allow it to sit on the cast iron.

You said this was an old gravity system but you must have a circulator on this, no? Or are you still operating it as a gravity system?

hot_rod

A look inside will tell if it has been condensing. Deposits on or under the burners for example. Any corrosion on the vent piping?

iridium

Thanks for the replies. Some comments below. I installed the ecobee because there were separate thermos for the AC retrofit and the boiler. I wanted to combine them and add a little bit of smarts (I already had the ecobee from my prior apartment that used forced air).

Jamie Hall said:

Basically you want as long a run time as you can with those things. Make sure you do that; I seem to recall the Ecobee has an option to set one cycle per hour (the old Honeywell had an anticipator, which worked better if it was properly set).

It's a funny thing about those old time massive teakettles. Condensation just didn't bother them much -- too much iron -- unlike the new tinplate ones.

And no, you can't put a bypass valve on a gravity circulation system. No pump.

One thought I had was forcing the cycle times to be even longer by increasing the setpoint and the heating threshold (1.5F currently). The temperature would swing a bit more but it would take a longer run to cover the difference. Would that make sense to do?

Another thought I had was picking up a 2nd aux temp sensor for the ecobee and excluding the ecobee itself from the temp calc. The ecobee (downstairs) heats faster and cools faster than my upstairs sensor. Its mounted on a wall that is shared with the boiler room so it could be picking up some heat there an stopping the heat call a little early.

The old thermostat was a Honeywell Chronotherm (I?). Anticipator was set to .7. I don't have much data on how it ran with that, but I do remember some short cycling (a few minutes) and a nice constant clicking noise coming from it. What about the old anticipator works better?

There is a circulator on the return in my system right next to the boiler. As far as I can tell it runs whenever there is a call for heat. No wait for boiler to come up a bit as I have seen some systems might do.

gyrfalcon said:

When measuring with IR gun, beam at black or other matte/ painted metals, bare copper will give inaccurate reading.  

Yeah I did notice that copper wasnt giving good temps.

pedmec said:

The long run cycle is drying out the cast iron. Your most like only getting condensation on start-up but eventually when it reaches steady state and the flue gas starts to increase in temperature above the dew and it will dry it out. Not allow it to sit on the cast iron.

You said this was an old gravity system but you must have a circulator on this, no? Or are you still operating it as a gravity system?

So even if the boiler temperature is below 140F by the end of the cycle it would be drying it out?

There is a circulator on the return at the boiler.

hot_rod said:

A look inside will tell if it has been condensing. Deposits on or under the burners for example. Any corrosion on the vent piping?

I'll take a look and report back. There is some white corrosion on the baffle in the damper, but past that what I can see looks ok. I hadn't looked at the burner tubes.

iridium

Me putting "gravity system" in the title might be incorrect. I just assumed since I have old large cast iron radiators that it was gravity. The house is cape code construction carriage house built in 1913 in PA. No idea when heat was installed. Virtually no insulation in the attic and no access from inside or outside to that attic. In summer my ceilings were measuring 100F when the sun was overhead. At least the second floor has some newer windows.

Edit: It just finished a 45 minute cycle that I captured some data for. Boiler temp started at 80F and climbed the whole time to finish at 145F. Final return temp was 115F.

EBEBRATT-Ed

If it has been that way since 1979 (if it ain't broke don't fix it) leave it alone

mattmia2

@Jamie Hall means the older mechanical thermostats where the anticipator was a resistor that heated the element to cause it to shut off a bit before reaching the setpoint. A Chrontherm is a digital thermostat where some sort of algorithm does the anticipating.

iridium

EBEBRATT-Ed said:

If it has been that way since 1979 (if it ain't broke don't fix it) leave it alone

Yeah since I'm renting I won't be changing any pipes. I'm just trying to understand how it could have lasted so long and make sure my ecobee setup isn't going to kill it. Really I started noticing all of this and researching because I was wondering if an outdoor reset would make sense for the system. With the current weather and water temps it seems like the answer would be no.

iridium

mattmia2 said:

@Jamie Hall means the older mechanical thermostats where the anticipator was a resistor that heated the element to cause it to shut off a bit before reaching the setpoint. A Chrontherm is a digital thermostat where some sort of algorithm does the anticipating.

The chronotherm I have is definitely not digital haha. Its one of these.

https://ids.si.edu/ids/deliveryService?max_w=800&id=NMAH-RWS2011-00779

mattmia2

yeah that one uses the resistor type anticipator

outdoor reset would make things worse unless it does it by mixing.

bburd

A high mass system like that doesn’t need outdoor reset, the water temperature will vary naturally with demand due to the enormous amount of water and iron to be heated.

mattmia2

Outdoor reset would work beautifully with the old gravity system but it wouldn't work well with that boiler, the water would have to be cooler than is safe for that boiler most of the time. It would be great with a mod con. It would just be warm enough to keep the house at temp all the time.

pedmec

I grew up with that thermostat as a kid. Had to set the trippers on the timer inside.

iridium

Yeah I understand that outdoor reset would basically never come into the picture for this current system now. I guess I was thinking it fired and hit 180F all the time when it didn't need to, but it'll never be reaching high temps with so much mass.

Any thoughts on getting longer cycle times? Or maybe I don't need to chase longer cycle times assuming the system has been running like this for over 40 years. The only difference is the ecobee.

My suspicion is that I am already getting longer cycle times with the ecobee because of the temperature threshold. Even those cycles barely seem to bring the outlet temperature up to 140F at the end. Conventional thinking says that is bad for the non condensing boiler.

Thinking about it more... I am not sure how a cast iron radiator system like this could generate the heat wanted and keep the return temperature above 140. I don't think you'd ever want the radiators to get to temperatures in the high 100s. Which leaves me wishing it had some sort of bypass/mixing valve.

I could switch back to the old honeywell to see how that behaves, but not as easy to collect the data of course.

WMno57

My 75 year old boiler operates the same way. I shut it down over the summer. It condenses like crazy the first time I start it up in the fall. After that, dry all winter. Warm start. Gas power burner moves air through the boiler and dries it out. No primary secondary. Burner continues to run after thermostat is satisfied. Burner stops when aquastat is satisfied.
105 year old 2 1/2 inch nominal gravity pipes. Huge cast iron radiators. I do have a circulator on the back of the boiler. Not pumping away.
I burn more methane, but I'm not buying a new boiler every 10 years. Which is better?

iridium

WMno57 said:

Burner continues to run after thermostat is satisfied. Burner stops when aquastat is satisfied.

Mine shuts off when the thermostat is satisfied. If it satisfied the aquastat (set at 175) there'd be a huge overshoot?

WMno57

No overshoot in room temperature. On my system the thermostat controls the circulator. The aquastat controls the burner. They don't communicate with each other. Sometimes the burner will fire up when there is no call for heat from the thermostat. Warm start. Not efficient. 75 year old boiler.

mattmia2

If it got the whole system up to 180 it would overshoot. If the boiler was warm start and stayed at say 160 or even 180, the boiler will cool down quickly with the cool return water from the system so it won't get the system up to anywhere near the aquastat setpoint.

If the boiler is warm start you need a flow check to keep the system from heating by gravity flow when the circualtor is off.

Another option for both is to slow the flow way down so that the boiler stays well out of the condensing range but the energy is supplied to the system in the form of lower flow and higher temp.

hot_rod

A classic example of where and how the heat emitters dictate to boiler operating condition, not vice versa.

All hydronic systems strive for thermal equilibrium. How and when. the reach that condition depends open the boiler to emitter relationship.

High mass systems work best with constant circulation as opposed to on/ off heat calls throughout the day. Makes it harder to maintain a even room temperature.

iridium

mattmia2 said:

If it got the whole system up to 180 it would overshoot. If the boiler was warm start and stayed at say 160 or even 180, the boiler will cool down quickly with the cool return water from the system so it won't get the system up to anywhere near the aquastat setpoint.

If the boiler is warm start you need a flow check to keep the system from heating by gravity flow when the circualtor is off.

Another option for both is to slow the flow way down so that the boiler stays well out of the condensing range but the energy is supplied to the system in the form of lower flow and higher temp.

It's a cold start system. I don't have any means to slow the pump down currently. It seems like I'd need some kind of new controller?

hot_rod said:

A classic example of where and how the heat emitters dictate to boiler operating condition, not vice versa.

All hydronic systems strive for thermal equilibrium. How and when. the reach that condition depends open the boiler to emitter relationship.

High mass systems work best with constant circulation as opposed to on/ off heat calls throughout the day. Makes it harder to maintain a even room temperature.

Link for source of pics/text: https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_23.pdf

By work best do you mean for comfort, efficiency, or both?

With the high mass system it seems you'd want to run the circulator all the time and run a low water temperature to provide consistent heat. Of course the old boiler does not like low water temps.

I guess really this all boils down to is trying to find the most efficient way to run this system in its current form. No modifications to piping (I'm renting), electronics mods or controller are a possibility.

mattmia2

You can use a ball valve or globe valve to throttle the flow. Some boilers control the circulator on an aquastat that only runs it when the boiler is above a certain temp.

Efficiency and comfort are best when the supply water temp matches the heat loss of the house but that requires a primary secondary scheme with a controlled mixing valve or injection pump controlled on outdoor temp with a conventional boiler.

hot_rod

iridium said:

mattmia2 said:

If it got the whole system up to 180 it would overshoot. If the boiler was warm start and stayed at say 160 or even 180, the boiler will cool down quickly with the cool return water from the system so it won't get the system up to anywhere near the aquastat setpoint.

If the boiler is warm start you need a flow check to keep the system from heating by gravity flow when the circualtor is off.

Another option for both is to slow the flow way down so that the boiler stays well out of the condensing range but the energy is supplied to the system in the form of lower flow and higher temp.

It's a cold start system. I don't have any means to slow the pump down currently. It seems like I'd need some kind of new controller?

hot_rod said:

A classic example of where and how the heat emitters dictate to boiler operating condition, not vice versa.

All hydronic systems strive for thermal equilibrium. How and when. the reach that condition depends open the boiler to emitter relationship.

High mass systems work best with constant circulation as opposed to on/ off heat calls throughout the day. Makes it harder to maintain a even room temperature.

Link for source of pics/text: https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_23.pdf

By work best do you mean for comfort, efficiency, or both?

With the high mass system it seems you'd want to run the circulator all the time and run a low water temperature to provide consistent heat. Of course the old boiler does not like low water temps.

I guess really this all boils down to is trying to find the most efficient way to run this system in its current form. No modifications to piping (I'm renting), electronics mods or controller are a possibility.

I feel comfort is best with the least amount of temperature swing. Efficiency should be best with long run cycles compared to on/ off.

The formula for cycle efficiency is total heat output over a timed period ÷ energy content of fuel consumed over that period


You may not be geared to get that data, however

Run fraction you could calculate burner on time÷ total elapsed time.

If you know the lowest turndown and the lowest load say a 10,000 load, turndown at 46,000.
10,000 ÷ 46,000 .21 or 21%

The key to mod con efficiency is low return temperature to keep 'em condensing. Low return at low turndown will be the best efficiency. The high ratio of heat transfer rate per unit of HX surface area.

iridium

Yeah but what things could I do to the existing system to get better efficiency.  It's not a mod con.  Old boiler, high mass system.

Force longer cycles with thermostat? get a smarter aquastat, more advanced circulator control that doesn't just do on off with heat command and burner, ??

mattmia2

reducing the heat loss of the building is by far the most effective way to increase efficiency

hot_rod

iridium said:

Yeah but what things could I do to the existing system to get better efficiency.  It's not a mod con.  Old boiler, high mass system.

Force longer cycles with thermostat? get a smarter aquastat, more advanced circulator control that doesn't just do on off with heat command and burner, ??

Have someone come out with a combustion analyzer clean, test and adjust as best you can with what you have.

It's the building as others have mentioned that drives fuel consumption. The less the building loses, the less you $$ to heat it. Spray foam cans can reduce air, infiltration leaks, one of the biggest energy thieves.

iridium

Guess I'll borrow the FLIR from work and have some fun.

And yeah the place is poorly insulated.  Kneewalls upstairs where you can see the roof slats in the cubby, ground floor is wood floor with no insulation underneath over a slab (likely uninsulated slab), likely nothing in the attic.

hot_rod

Walk around the outside of the home with the IR camera to get ideas of where you might upgrade insulation, upgrade the homes efficiency first, that saves energy from now on.

A blower door test can also be an eye opener, sealing air leaks is usually the least expensive building upgrade. Sometimes as simple as adjusting a door strike to make the door seal against weatherstrip better.