What size Weil-Mclain cast iron replacement boiler with indirect water heater?

[deeMatrix]

Hi,
We are considering finally replacing our Weil-Mclain CGA5 cast iron boiler that I posted on here two years ago that has served us very well for 27 years but has been making boiler knocking/percolating type noises during fire stage. After evaluating a few contractor proposals we have decided we are not comfortable with mod-con units with our micro zones, contractors experience, higher cost, etc. so we are planning to go with a similar type cast iron boiler but add in an indirect water heater as part of the project.

We had a Manuel J performed which indicated around 68000 BTU heat loss. I also did the dry bulb approach last year that Dana outlined in an article a while back using my actual numbers and it arrived at around 62500 BTU/hour @ 60F.

One contractor indicated that the Manuel J heat loss number was on the borderline between a CGA3 (59000 BTU out) and CGA4 (88000 BTU out) but thought it was too close for comfort so wanted to go with the CGA4. The CGA5 is 117000 BTU out which the numbers show is oversized but our existing one has served us quite well for 27 years but some short cycling at times with our micro zones.

One contractor who we like is indicating that he will put in the CGA4 but indicates he would personally stick with a CGA5 with the Aqua Plus 45 indirect water heater as part of the solution. As indicated, we have had great success in our home with our current CGA5 but based on the heat loss/dry bulb numbers it shows the current boiler was way oversized.

Obviously we are a little confused and not sure if we should still tell him to go with the CGA4 or go with what has worked and what he would personally go with, especially in light of the addition of the the new 45 gallon indirect water heater. Thoughts?
Thanks in advance.

deeMatrix

 

[Dana]

Don't give up on the boiler just yet. The knocking/banging (aka "kettling") is probably related to lime deposits on the water side of the heat exchanger plates, which can often be treated with additives to the heating system water with purpose made deliming products (eg Fernox F1. or F3 if it needs a more thorough cleaning. F3 needs to be flushed after treatment, F1 does not.) Even if you spend $150 trying out a few boiler treatments it's a lot cheaper than buying a new boiler.

Another common cause of kettling is low system pressure. If it had normally been run at 10-12 psi see what happens if you raise the system pressure to 14-16 psi.

If that fails...

For the same or less money as a CG4 you could go with a small stainless fire tube modulating condensing boiler like HTP's UFT-080W. (Westinghouse sells the identical boiler as the WBRUNG080W.) Not only will it run at higher combustion efficiency, by bricking up the flue (eliminating a 24/365 air infiltration driver) and running at a lower temperature, the actual heat load number will come down a bit. It has more output than the CGa-3, but not quite as much as the -4. Internet pricing on those boilers is $1600-1800, the same range as the CGa-4. For $100-200 more you could get the 100K version, the UFT-100W /WBRUNG100W, and have almost as much output as the CGa-5 at high fire, yet still be able to throttle back to 10K-in/9.5K-out at low fire. These boilers are also internally plumbed with a second port for supporting an indirect water heater, which simplifies the installation plumbing as compared to any other boiler.

If going with cast-iron the ASHRAE recommendation is to install a 1.4x oversize factor. So if the measured load is 62,500 BTU/hr sizing the boiler up to 1.4 x 62,500= 87,500 BTU/hr would be reasonable, which in the CGa series puts you dead-on the 88K output of the CGa-4, not the -5. The presence/absence of an indirect water heater makes no difference in the boiler sizing unless you're filling 200 gallon spa tubs frequently.

The UFT-100W puts out a hair more than the CGA-4 at high fire, but since it's a modulating condensing boiler the minimum output rate is at least as important as the max rate for sizing mod-con boilers. How much radiation do you have on your micro-zones, zone, by zone? If it's high volume radiators (not fin-tube baseboard) it almost doesn't matter- the thermal mass of the water + iron keeps it from short cycling, but if it's all low mass heat emitters it can matter quite a bit.

 

[Sponsor]

 

[deeMatrix]

Don't give up on the boiler just yet. The knocking/banging (aka "kettling") is probably related to lime deposits on the water side of the heat exchanger plates, which can often be treated with additives to the heating system water with purpose made deliming products (eg Fernox F1. or F3 if it needs a more thorough cleaning. F3 needs to be flushed after treatment, F1 does not.) Even if you spend $150 trying out a few boiler treatments it's a lot cheaper than buying a new boiler.

Another common cause of kettling is low system pressure. If it had normally been run at 10-12 psi see what happens if you raise the system pressure to 14-16 psi.

If that fails...

For the same or less money as a CG4 you could go with a small stainless fire tube modulating condensing boiler like HTP's UFT-080W. (Westinghouse sells the identical boiler as the WBRUNG080W.) Not only will it run at higher combustion efficiency, by bricking up the flue (eliminating a 24/365 air infiltration driver) and running at a lower temperature, the actual heat load number will come down a bit. It has more output than the CGa-3, but not quite as much as the -4. Internet pricing on those boilers is $1600-1800, the same range as the CGa-4. For $100-200 more you could get the 100K version, the UFT-100W /WBRUNG100W, and have almost as much output as the CGa-5 at high fire, yet still be able to throttle back to 10K-in/9.5K-out at low fire. These boilers are also internally plumbed with a second port for supporting an indirect water heater, which simplifies the installation plumbing as compared to any other boiler.

If going with cast-iron the ASHRAE recommendation is to install a 1.4x oversize factor. So if the measured load is 62,500 BTU/hr sizing the boiler up to 1.4 x 62,500= 87,500 BTU/hr would be reasonable, which in the CGa series puts you dead-on the 88K output of the CGa-4, not the -5. The presence/absence of an indirect water heater makes no difference in the boiler sizing unless you're filling 200 gallon spa tubs frequently.

The UFT-100W puts out a hair more than the CGA-4 at high fire, but since it's a modulating condensing boiler the minimum output rate is at least as important as the max rate for sizing mod-con boilers. How much radiation do you have on your micro-zones, zone, by zone? If it's high volume radiators (not fin-tube baseboard) it almost doesn't matter- the thermal mass of the water + iron keeps it from short cycling, but if it's all low mass heat emitters it can matter quite a bit.

 

[deeMatrix]

Thanks Dana as always for your thorough response. I have tried cleaning with the Rhomar treatment which requires flushing and then added the subsequent Rhomar conditioner 2 years ago. The noise reduced for a while but then returned.

Last year I tried the Oatey boiler cleaner and similar results where it reduced noise initially then returned. I just did the Oatey again last week since I had another quart and so far noise is significantly reduced but running system and waiting to see if it returns. I have yet to try Fernox but perhaps I should. I have raised system pressure a bit in the past but didn't do much to abate noise.

As for the numbers I provided, I should have indicated that the 62500 BTU/hour @ 60F dry bulb numbers INCLUDED the ASHRAE recommendation 1.4x oversize factor. Our number was actually 44,744 BTU/hour heat load calcuation at 60F.

Based on your comments if we were to go with the cast iron Weil-Mclain it would be the CG4 even with the indirect water heater which would still be oversized to a degree. One contractor we liked indicated the CG3 was there but too close so recommended the CG4.

As for mod/con regarding the house size and zoning we have a total of 194 feet of fin-tube baseboard element and 2 under cabinet Beacon Morris K42 kickspace heaters. The Beacon Morris K42 Kickspace Twin-Flo III heaters have a range of 1480-5240 BTU each.

House is ~3150 sqft. of living space with 5 zones split between 1st floor, 2nd floor and basement 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 kitchen 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 master bathroom under sink Twin-Flo III kickspace heater)

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

We truly appreciate your thoughts.
deeMatrix

 

[Dana]

If the actual load was indicating ~45K, any cast iron boiler solution should be no bigger than ~60K of DOE output. That puts you in the CGa-3, and definitely NOT the CGa-4. The CGa-4 would be slightly more than a 1.7x oversize factor for the load, whereas the CGa-3 would be a bit over 1.3x.

While AFUE testing assumes a 1.7 x oversize factor, it does NOT assume five zones and the extra cycling that induces. As a system it will be much better off at 1.3x oversizing, with longer but fewer burns and a much better duty cycle even when doing a lot of cycling during the shoulder seasons.

The ASHRAE 1.4x oversize factor is pretty arbitrary- you're never going to worry about getting cold at only 1.3x oversizing, and if the indirect is given priority by the zone controller, with the full 59K of boiler output going into the water heater it will already be up to temperature before you finish dressing after a shower, and never take long enough for the temperature in the house to drop even 1 degree. Only if you're running something like 5 back-to-back 12 minute showers would there be a noticeable dip in room temperatures, and then only if it's the coldest hour of the year.

It looks like you have 54' + 41' + 42' + 26' + 31' = 194' of baseboard plus a couple of toe-kicks of unspecified size. (Are they the Model 42, Model 84, or the Model 120?)

At a cool high-condensing 120F average water temp (AWT : 125F -out, 115F-return) typical baseboard delivers about 200 BTU/hr per running foot, so with a condensing boiler the baseboard alone would cover 200 x 194' = 38,800 BTU/hr, which is more than 85% of the design load. This means it's highly likely that you could run it in condensing mode 99% of the time and still have it covered, and beat the nameplate AFUE numbers for the boiler.

The minimum fire output of the UFT-80W boiler is about 7600 BTU/hr, so it can run at 95% efficiency with NO cycling with zones as short as 7600/200= 38 feet.

Since the bedroom zone with the 26' of baseboard also has the toe-kick in the bath that would deliver at least 1800 BTU/hr at those temperatures even if it were the smallest Model 42 it should pretty much balance even at 125F out, or at the worst case cycle VERY slowly when it's the only zone calling for heat.

The basement zone with the 31' of baseboard is only 7' or (7 x 200 = ) 1400 BTU/hr shy of balancing. The UFT-80W has about 25lbs of water init, and the rest of the plumbing could have another 3lbs (at least) call it 28lbs total. With 1400 BTU/hr (= 23 BTU/minute) of extra heat going into it the temperature would be slewing by 23BTU/28lbs= 0.8 F per minute, so even if it's set up for a 5F rise above set point before turning off the burner the minimum burn times would be 5F/0.8= 6.5 minutes per burn, which is not an efficiency robbing boiler-wrecking short cycle.

That passes the napkin-math test. It should be pretty easy to make the UFT-080W / WBRUNG80W work GREAT with your radiation & load. There will be some tweaking of the outdoor reset curve to ensure that it raises the output temp sufficiently to get enough heat out of the baseboard during cold snaps and the like, but you have plenty of radiation to keep it from short cycling, and with about 70,000 BTU/hr of output at maximum fire at non-condensing water temps there enough burner to keep the place warm even at all time record low temperatures.

Who performed the full Manual-J?

Can you scan the report (at least the summary pages) and post them?

With 194' of baseboard and two Model 42s, the 59,000 BTU/hr output of a CGa-3 would settle in at about 135F average water temp if all zones are calling for heat at once. That's getting pretty close to the condensing risk range, so if going with that boiler a system bypass branch should be installed at the boiler, mixing in some direct boiler output with the return water to keep the entering water temp at the boiler above 130F.

The Burnham ES2-3 has and 303B boilers have the same output as the CGa-3, but are internally self-protected for return water as cool as 110F without any external bypass plumbing, and could be simpler/cheaper to install. The power-vented Burnham ESC-3 has that built-in protection too, but only 52,000 BTU/hr of output which would be cutting it a bit too close.

 

[deeMatrix]

If the actual load was indicating ~45K, any cast iron boiler solution should be no bigger than ~60K of DOE output. That puts you in the CGa-3, and definitely NOT the CGa-4. The CGa-4 would be slightly more than a 1.7x oversize factor for the load, whereas the CGa-3 would be a bit over 1.3x.

While AFUE testing assumes a 1.7 x oversize factor, it does NOT assume five zones and the extra cycling that induces. As a system it will be much better off at 1.3x oversizing, with longer but fewer burns and a much better duty cycle even when doing a lot of cycling during the shoulder seasons.

The ASHRAE 1.4x oversize factor is pretty arbitrary- you're never going to worry about getting cold at only 1.3x oversizing, and if the indirect is given priority by the zone controller, with the full 59K of boiler output going into the water heater it will already be up to temperature before you finish dressing after a shower, and never take long enough for the temperature in the house to drop even 1 degree. Only if you're running something like 5 back-to-back 12 minute showers would there be a noticeable dip in room temperatures, and then only if it's the coldest hour of the year.

It looks like you have 54' + 41' + 42' + 26' + 31' = 194' of baseboard plus a couple of toe-kicks of unspecified size. (Are they the Model 42, Model 84, or the Model 120?)

At a cool high-condensing 120F average water temp (AWT : 125F -out, 115F-return) typical baseboard delivers about 200 BTU/hr per running foot, so with a condensing boiler the baseboard alone would cover 200 x 194' = 38,800 BTU/hr, which is more than 85% of the design load. This means it's highly likely that you could run it in condensing mode 99% of the time and still have it covered, and beat the nameplate AFUE numbers for the boiler.

The minimum fire output of the UFT-80W boiler is about 7600 BTU/hr, so it can run at 95% efficiency with NO cycling with zones as short as 7600/200= 38 feet.

Since the bedroom zone with the 26' of baseboard also has the toe-kick in the bath that would deliver at least 1800 BTU/hr at those temperatures even if it were the smallest Model 42 it should pretty much balance even at 125F out, or at the worst case cycle VERY slowly when it's the only zone calling for heat.

The basement zone with the 31' of baseboard is only 7' or (7 x 200 = ) 1400 BTU/hr shy of balancing. The UFT-80W has about 25lbs of water init, and the rest of the plumbing could have another 3lbs (at least) call it 28lbs total. With 1400 BTU/hr (= 23 BTU/minute) of extra heat going into it the temperature would be slewing by 23BTU/28lbs= 0.8 F per minute, so even if it's set up for a 5F rise above set point before turning off the burner the minimum burn times would be 5F/0.8= 6.5 minutes per burn, which is not an efficiency robbing boiler-wrecking short cycle.

That passes the napkin-math test. It should be pretty easy to make the UFT-080W / WBRUNG80W work GREAT with your radiation & load. There will be some tweaking of the outdoor reset curve to ensure that it raises the output temp sufficiently to get enough heat out of the baseboard during cold snaps and the like, but you have plenty of radiation to keep it from short cycling, and with about 70,000 BTU/hr of output at maximum fire at non-condensing water temps there enough burner to keep the place warm even at all time record low temperatures.

Who performed the full Manual-J?

Can you scan the report (at least the summary pages) and post them?

With 194' of baseboard and two Model 42s, the 59,000 BTU/hr output of a CGa-3 would settle in at about 135F average water temp if all zones are calling for heat at once. That's getting pretty close to the condensing risk range, so if going with that boiler a system bypass branch should be installed at the boiler, mixing in some direct boiler output with the return water to keep the entering water temp at the boiler above 130F.

The Burnham ES2-3 has and 303B boilers have the same output as the CGa-3, but are internally self-protected for return water as cool as 110F without any external bypass plumbing, and could be simpler/cheaper to install. The power-vented Burnham ESC-3 has that built-in protection too, but only 52,000 BTU/hr of output which would be cutting it a bit too close.

 

[deeMatrix]

Thanks again Dana for your guidance. I don't have the actual output of the Manual J but two different contractors who came in gave me similar results so I assume it was pretty reasonable. The dry bulb number I worked up based on your article was within 10% or so of it so that further confirmed in my mind the number must be pretty decent. As for the model number of the kicker they both are indeed the 42 model.

As an interesting sidenote, there were only 2 homes in our entire development when built in 1992 that installed baseboard which was coincidentally the exact model as mine. My home was built first and they installed the CGA5 while on the second one a year later they downsized it to a CG4 so it looks as though they realized at that point it was oversized.

Recently I spoke to the other homeowner and he had to replace his unit last winter as it started leaking and I saw his installation and noticed the new contractor he used put in a Burnham ES2 with a Bradford White indirect water heater. Just thought it interesting that you indicated the ES2 which has the same output as the CGa-3 (rather than even the CGa-4).

 

[Dana]

The ES2 series comes in a number of different sizes, but the smallest of that line, the three-plate ES2-3 is pretty much identical in output specs to the CGa-3.

The ES2-4 is nearly identical in output to the CGa-4, with a DOE output of 89K to the CGa-4's 88K.

I don't know how close you are to Howell Township, but Richard McGrath (who lives in Toms River) of Langans Plumbing & Heating LLC / Bluewater Mechanical Inc would have no problems getting that HTP mod-con installed & set up correctly. He posts on a number of web-forums (not too active on this one though), and clearly has a good grasp on boiler sizing, and how to design maximal efficiency & comfort heating systems. I'm sure there are other contractors up to the task if they're not close enough, or their proposal comes in out of budget.

 

[deeMatrix]

Dana, I reached out to Langans a few days ago and spoke to I believe Langan (John?) himself as don't believe it was Richard McGrath. I got the company name from this forum a year or two ago so they are on my list. He indicated they would come up to where I'm located so depending on how I go they'll be a consideration. At this point I'm still in cleaning mode to see if this resolves the kettling situation and after the latest addition of Oatey cleaner noise is much, much less now but need to see if it returns. Thanks again.

 

[deeMatrix]

Folks, we went with the Weil-Mclain CGa-4 with the Aqua-Plus 45 indirect water heater 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 and the boiler ran longer and cycled less often than with the prior CGa-5.

The boiler temperature was set to 180 degrees for our copper-finned baseboard heat and we set the indirect set at 140 with a mixing valve based on recommendations to avoid any potential for Legionella disease.

Now that it is summer though I am curious if the boiler setting should still remain at 180 or does it make sense to reduce it to say 160? The WM has a 20 degree differential as I understand it so if it were set to 160 the low point would be 140 which would be the same as the indirect. 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?

Thanks in advance for any perspectives.

 

[Reach4]

You are feeding this with chlorinated water? AFAIK, the legionella outbreaks were associated with water towers or cooling towers on buildings.

You should be able to properly sanitize your plumbing after doing work, and I don't see how legionella gets in to grow. I am not a pro.

 

[deeMatrix]

It is city water and comes through whole house water filtration system. Not really sure on Legionella but figured 140 degrees just in case. It would be great to get some opinions on this, as well as the CGa-4 temperature setting during the shoulder seasons where the boiler is only used to heat the indirect storage tank.

 

[deeMatrix]

Dana, could use your professional guidance on this.

There is an Economy Adjust setting on the Weil-Mclain boiler which delays the firing of the boiler to first see if the call for heat can be satisfied by existing boiler water temperature. It is set to Min but the manual indicates the preferred setting is Max. Not sure if this adds any value changing this?

Also, I timed the cycle time the last few times the indirect called for heat with the boiler set at 180 and it only fired until about 160 or so before shutting off and then the heat soak brought the boiler up to 180 on the dial.

Since the boiler is only being used for the indirect water heater this time of year wouldn't a lower setting say 170 or even 160 (which is 20 degrees higher than the 140 setting on the indirect. Mixing valve set at 120) allow the boiler to run a longer run time which may be more efficient and better than short cycling the boiler?

Thoughts please?