Recommended Settings to Run WM Boiler for Indirect during Shoulder Seasons

[deeMatrix]

Thanks in advance.

We had a new Weil-Mclain CGa-4 cast iron boiler with the Aqua-Plus 45 indirect water heater installed in the fall which ran great throughout the winter. Everything worked as expected with the indirect on a priority zone for DHW so we always had enough hot water. The boiler temperature was set to 180 degrees for our copper-finned baseboard heat and the indirect set at 140 to help avoid any potential for Legionella disease with a mixing valve set at 120.

Now that it is summer should we keep the boiler set at 180, or does it make sense to reduce it, or does it just make sense to leave it as is since talking pennies and better for boiler to be set at 180 all year round?

Also, there is an Economy Adjust setting on the Weil-Mclain boiler which delays the firing of the boiler to determine if the call for heat can be satisfied by existing boiler water temperature. Upon inspection, it was set to "Min" from the onset but the manual indicates the preferred setting is "Max". Not sure if this adds any value in changing this?

Any perspectives would be greatly appreciated.
deeMatrix

 

[Sylvan]

A tempering valve (mixing) is not considered an anti scald device Setting the temperature 140 or above for killing bacteria etc is a great idea

 

[Sponsor]

 

[Jadnashua]

Your boiler set point being higher will mean a faster WH recovery. SEtting the supply temp on the boiler too low could cause the return water to get into the condensing range, which is bad for longevity. The higher the boiler's set point, the more standby losses.

Does the installation manual have any suggestions? I might consider calling the boiler's tech support line.

 

[deeMatrix]

Thanks for responses so far. I have a call into Weil-McLain but hard to get responses these days with the ongoing crisis. The manual doesn't say much although 180 is typical for the copper finned baseboard but no real info on when just using the boiler during the shoulder seasons only for the indirect.

As for the "Economy Adjust" setting, this is confusing as this automatically adjusts a time delay period to turn on the boiler during a call for heat as perhaps there is enough temperature to satisfy without firing up the boiler. The manual says the preferred setting is "Max" but the installer left it at "Min" or effectively off/no delay. I have a txt out to them and curious if any rationale for it being set this way but curious if any others had any perspective.

 

[Sylvan]

[

Your boiler set point being higher will mean a faster WH recovery. SEtting the supply temp on the boiler too low could cause the return water to get into the condensing range, which is bad for longevity. The higher the boiler's set point, the more standby losses.

Does the installation manual have any suggestions? I might consider calling the boiler's tech support line.

As for the "Economy Adjust" setting, this is confusing as this automatically adjusts a time delay period to turn on the boiler during a call for heat as perhaps there is enough temperature to satisfy without firing up the boiler. The manual says the preferred setting is "Max" but the installer left it at "Min" or effectively off/no delay. I have a txt out to them and curious if any rationale for it being set this way but curious if any others had any perspective.[/QUOTE]

Actually if the water is too high the coefficent of expansion per degree of temperature can cause undo stress on the piping system especially copper. This is why sometimes you hear a pinging sound with slant tubing

Even though ASME and NBBI considers a low pressure boiler to be 15 PSI Steam or 160 PSI @250 Deg F Hydronc boiler there is the
possibility of an explosion if the water temperature exceeds 212 deg F and flashes into steam

You may want to consider non electric zone valves if you have a two pipe system

I live right across from Fort Leee so we basiclly have the sae tempertures

Your heating temperature 180 Deg is what I have with a 20 deg Delta

 

[Fitter30]

Minimum water temp is 140* return temp on any cast iron boiler.

 

[Dana]

Minimum water temp is 140* return temp on any cast iron boiler.

That's true for oil-fired cast iron, but many/most gas-burners handle 130F without a problem (even when the literature recommends 140F.) It's nearly impossible to get natural gas exhaust condensation on the boiler plates with 130F return water even when you want the condensation for efficiency, even at better controlled air/fuel mixtures (with much less excess combustion air) in a modulating-condensing boiler. The W-M CGa series literature says 140F, but there are existence-proofs of 30 year old CGa boiler running without damage with 130F entering water temps.

That said, you're pushing your luck setting the high-limit to 140F for the summer. Try 145 or 150F instead.

How much baseboard (zone by zone) do you have on this CGa-4?

It takes about 175' of baseboard to emit the full 88K DOE output of that beast at 170F average water temp (180F out, 160F return), and about 250' of baseboard at an average water temp of 140F (150F out, 130F return.) It's unlikely that there is enough baseboard on each zone (or even the whole house) to emit the full output, so it's going to be cycling a bit, possibly even short-cycling on zone calls if there are a number of stubby zones with short runs of baseboard.

The total 88,000 BTU/hr output is much higher than the space heating loads of almost all normal sized homes that have some amount of insulation and double-pane windows (or storms over single-panes.) That's enough burner to keep my ~2400' antique 2x4 framed house + 1600' of insulated basement at 68-70F even when it's cooler than -80F outside (a temp not seen in my neighborhood since the last ice age), but I only have enough radiation to emit about half that at the <130F water temps I'm running. If your curious as to just how oversized that boiler is for your house, run a fuel-use based heat load calculation.

The primary reason this boiler has been up-sized to the CGa-4 is most likely for domestic hot water service. Most houses in NJ would be better off with the CGa-25 (half the output of the -4), provided there isn't so much baseboard that it's running chronically low return water temps (though that can usually be dealt with with bypass plumbing to mix boiler output with return water using a system-bypass branch to keep the entering water temps above 130F, or 140F.)

 

[deeMatrix]

How much baseboard (zone by zone) do you have on this CGa-4?

Thanks Dana. As usual a very thorough response.

From what I gather you are suggesting that I could set my boiler aquastat to 150 during the shoulder seasons with my indirect set for 140 without any issues?

Also, is the "Economy Adjust" dial that is presently set at "Min" worth increasing towards "Max" as preferred in the manual to delay the firing of the boiler if the boiler water temperature is high enough to satisfy the call for heat? I could see this potentially being worthwhile during the heating months with five zones but not sure of value during the summer, indirect water heater only period.

See following regarding our baseboard sizing. Yes we have some stubby zones. You responded to a prior post of mine last year and thought that we might be better off with CGa-3 than the 4 but the Manual J that was performed on our home indicated it was close for the CGa-3 so it was decided to go with the CGa-4. Not sure how much the indirect water storage tank came into the equation since it is on a priority zone but was another factor that tilted the decision. See the following regarding your question of our baseboard:

House is ~3150 sqft. of living space with 5 zones split between 1st floor, 2nd floor and basement, all with copper-finned baseboard as follows:

1st floor ~1400 sqft. living space divided into 2 zones:
Family room, Kitchen/breakfast area foyer and powder room ~1025 sqft. (54' baseboard and under sink vanity Twin-Flo III kickspace heater
Dining room/Living room ~375 sqft. (41' baseboard)

Second floor ~1050 sqft. living space divided into 2 zones:
3 bedrooms, hall, main bath, laundry closet ~650' sqft. (42' baseboard)
Master bedroom, master bath and closet ~400 sqft. (26' baseboard and bathroom under sink vanity Twin-Flo III kickspace heater)

Heated Basement ~700 sqft. living space (31' baseboard)

Thanks,
deeMatrix

 

[Fitter30]

The average setting for the aquastat (the temperature control device on a boiler) for a forced hot water system is 180°F. It can be raised as high as 210°F if needed in severe weather. For systems that use coils to heat domestic hot water, the high limit setting is 210°F and the low limit setting 140°F. A differential setting of 15°F is recommended for the optimum amount of domestic hot water.

 

[deeMatrix]

Dana,

Any thoughts based on the questions I asked and the baseboard info I provided you?

Thanks,
deeMatrix

 

[Dana]

Thanks Dana. As usual a very thorough response.

From what I gather you are suggesting that I could set my boiler aquastat to 150 during the shoulder seasons with my indirect set for 140 without any issues?

That's right. Even with the indirect set to 140F it's unlikely to be sending sub 130F water back into the boiler, but MEASURE it (where the return water enters the boiler) just to be sure. A $50 pistol-grip infrared thermometer works pretty well on black-iron plumbing, but on shinier stuff (or even not-so-shiny copper) put a spot of spray paint (any non-metalic cover) where you want to measure the temp.

Also pay attention to the burner as the indirect recovers after a big draw (like a shower or tub fill). The heat transfer rate across the heat exchanger coil might not be high enough to cover the full boiler output with only a 10F temperature difference, which would potentially cause some short cycling. If it's cycling the burners on/off during the recovery, bump the temp high-limit temp on the boiler up 5F-10F.

Also, is the "Economy Adjust" dial that is presently set at "Min" worth increasing towards "Max" as preferred in the manual to delay the firing of the boiler if the boiler water temperature is high enough to satisfy the call for heat? I could see this potentially being worthwhile during the heating months with five zones but not sure of value during the summer, indirect water heater only period.

It's been awhile since I looked at the operational details of that crude economizer control, but my recollection is in line with your thinking. It'll make a difference during the heating season with your chopped-up zoning, not so much when the only zone is the indirect.

See following regarding our baseboard sizing. Yes we have some stubby zones. You responded to a prior post of mine last year and thought that we might be better off with CGa-3 than the 4 but the Manual J that was performed on our home indicated it was close for the CGa-3 so it was decided to go with the CGa-4. Not sure how much the indirect water storage tank came into the equation since it is on a priority zone but was another factor that tilted the decision. See the following regarding your question of our baseboard:

House is ~3150 sqft. of living space with 5 zones split between 1st floor, 2nd floor and basement, all with copper-finned baseboard as follows:

1st floor ~1400 sqft. living space divided into 2 zones:
Family room, Kitchen/breakfast area foyer and powder room ~1025 sqft. (54' baseboard and under sink vanity Twin-Flo III kickspace heater
Dining room/Living room ~375 sqft. (41' baseboard)

Second floor ~1050 sqft. living space divided into 2 zones:
3 bedrooms, hall, main bath, laundry closet ~650' sqft. (42' baseboard)
Master bedroom, master bath and closet ~400 sqft. (26' baseboard and bathroom under sink vanity Twin-Flo III kickspace heater)

Heated Basement ~700 sqft. living space (31' baseboard)

Thanks,
deeMatrix

The stubby zoning is definitely an issue, but there's at least some thermal mass to work with in the CGa-4. A data-logger tracking the burner's gas valve operation or the stack temperature would give some idea as to the average burn time, and total duty cycle. With a mid-efficiency gas-burner minimum burn times of 5 minutes only knock about 1% off the AFUE performance, but if they're averaging sub-3 minutes it may be worth doing something about it. While many "smart" thermostats have datalogging capabilities, they only log the lengths of the call for heat, and can't tell you what the burner is doing.

 

[deeMatrix]

Thanks Dana for getting back on this. I think we have a plan.

 

[deeMatrix]

"Even with the indirect set to 140F it's unlikely to be sending sub 130F water back into the boiler, but MEASURE it (where the return water enters the boiler) just to be sure."

Dana, WHEN do I measure the return temp back into the boiler?

If boiler is off for a while the return water temp will be lower than 130F but do I measure it after the boiler has been heating the indirect for a period of time to see the return temp?

 

[Dana]

"Even with the indirect set to 140F it's unlikely to be sending sub 130F water back into the boiler, but MEASURE it (where the return water enters the boiler) just to be sure."

Dana, WHEN do I measure the return temp back into the boiler?

If boiler is off for a while the return water temp will be lower than 130F but do I measure it after the boiler has been heating the indirect for a period of time to see the return temp?

Give it a couple of minutes after the initial firing to start measuring the entering water temp (EWT) at the boiler. Most gas fired cast iron is tolerant of cold starting, and it takes a couple of minutes to bring the thermal mass of a tepid idling boiler up to temp. As long as EWT is north of 130F for most of the burn time, there won't be residual condensation left on the boiler plates at the end of the burn. If the EWT never breaks 125F until the last minute or two it's a problem that may require more than bumping up the boiler temp.