Near boiler piping/replacement boiler

katman

Hi everyone. I have a 20 yr old Weil Mclain 5 section boiler that is oversized for my house.
I'm debating if I should replace it with a smaller boiler such as a Buderus G115WS/3, or keep this boiler and repipe it.

House has three heating zones and an indirect zone. Indirect is wired from the Taco relay to the Hydrostat 3250 using ZC/ZR, and set for indirect priority. Each zone has about 50 ft of fin tube baseboard length. Oil use is about 1,000 gallons a year. House is about 1,800 sq ft.

The existing boiler piping has some of the following issues:
- The circulators for the boiler and indirect are both on the return
- The return pipes for all heating zones connect into 1" pipe, then this goes into 1 1/4" after the circulator and into the boiler at 1 1/2"
- The supply pipe reduces from 1 1/2" into 1 1/4", goes into the spirovent and then to the manifold for the zone valves on 1" pipe. There also appears to be some sort of balancing valve in the manifold pipe before the zone valves.

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I figure I have a few options:

1) leave everything as is since the boiler works, and nothing is leaking yet.

2) Replace boiler with Buderus G115WS/3, repipe supply to 1 1/4" manifold reduced to 3/4" for each zone and repipe return to 1". I would plan to still use zone valves instead of individual circulators.

3) Keep existing boiler, install circulators on supply, repipe supply to 1 1/4" manifold reduced to 3/4" for each zone and repipe return to 1 1/4" before it goes back into the boiler at 1 1/2"

I've attached some pictures of the current boiler and piping.

Thanks!

ethicalpaul

The answer is: 1

EBEBRATT-Ed

If it's not broke don't fix it.

Get quotes on new boilers (you will be shocked). Then start saving. Do an accurate heat loss and get the right size equipment and the right contractor.

Consider an Energy Kinetics boiler.

Mad Dog_2

Run to failure..unless you have extra disposal income....Mad Dog

hot_rod

The piping size is adequate for the load you have connected. 100' of fin tube could supply about 55,000 BTU/hr. Seems like plenty for 1800 square feet? No sense in having a boiler sized larger that the fin tube can put into the space. So a 60- 75,000 BTU/hr boiler would be adequate.

If your current boiler is twice that size, 120,000 or larger it probably short cycles and runs 70% efficiency range.

Alan (California Radiant) Forbes

Three zones with 50'/zone = 150' x ~500 BTU/ft. @ 180° = 75,000 BTU. One inch pipe is fine for that load.

If you really want to do something, pipe it primary-secondary to keep the large boiler happy.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1859413#Comment_1859413

or a buffer tank. a buffer tank is probably the only thing you could do that might come close to paying for itself

katman

Thanks everyone for your comments and suggestions.

Some of the near boiler piping is looking like it's ready to leak, so that's why I was considering at least having a buddy who's a plumber replace some of the piping for me.

The decision I will need to make is do I just replace what pipes needs to be replaced, or dig deeper by doing stuff such as moving the circulators to the supply, remove that inline purge/balancing valve, and add a 1 1/4" supply manifold to 3/4" to feed the zone valves while the piping is being fixed.

I'm trying to avoid any unexpected breakdowns of the boiler during the winter and be proactive.

The circulators are a little sketchy to me with the way that they're piped into the return, so I put the wood under them to take the weight off of that return pipe.

Here are the specs on the boiler:

P-WTGO-5
Series no 3
I=B=R Input LT oil, gph 1.45
D.O.E Htg Cap (Water) Btu/hr 175,000
Net I=B=R Rating (Water) Btu/hr 152,000

I used to use an outdoor reset with the hydrostat 3250, but the boiler would hit the lowered high limit too quickly.
I then removed the ODR, and set the high limit differential to 30 with a high limit of 175.
This got the boiler to run for about 7-8 minutes while zones are calling before hitting high limit.
The boiler also only runs for about 5 minutes when the indirect is calling before high limit is reached.
I also have thermal pre-purge enabled on the hydrostat 3250 to make use of the latent heat in the boiler.

I downsized the nozzle from a 1.25 to a 1.10
I'm burning about 1,000 gallons of oil a year.

I know that this short cycling isn't efficient, but I just want to make sure that this won't harm the boiler.
Then again, it is 20 years old and still going……

I replaced a lot of the parts on the carlin burner as well, and the boiler runs good as it is.

I'm going to see if I can find someone in CT who can come see what I have, and give me some consultation on what makes the most sense for me to do.

hot_rod

A heat load would add some more info to the question. 1800 sq ft X 25 btu/ ft guesstimate= 45,000BTU/hr required. That is on the coldest day.

80% of the heating season the load could be in the 30,000 range. So the boiler 152,000 you have could be 3-4 maybe 5 times what you need.

While` not hydronically ideal for that boiler, the circs are not causing efficiency issues on the return, unless the system has noisy air issues?

Here is a simple buffer piping, direct to load method. Indirect on priority with its own circ.

EdTheHeaterMan

The WM WGO-5 has a rated input of 1.45 GPH. That same boiler can be fired at 1.20GPH when it has a model number of WGO-5RD. That is a 5 section boiler that comes from the factory with a oil burner nozzle of 1.00 GPH and a pump pressure setting at 145 PSI.

Weil McLain allows you to reduce the fire rate by 15% and as much as 20% on most of their boilers by adjusting the gas pressure on Gas Fired units and reduced nozzle size on Oil Fired units. I might attempt to use a .85 GPH nozzle at 45 PSI. After checking the stack temperature and other combustion test numbers, you may find that you can get good numbers with the boiler firing at 1.02 GPH which would end up with a AHRI NET output of 107K BTUh. That will bring you from 3 times too big down to twice as big as needed. That will then reduce your short cycling by 30ish%.

Now you may end up with flue gas condensation as a result of this change, but you may not. If you get the stack temperature to 350° within the first 3 minutes of operation, you will probably be alright. If you can't Then check the return water temperature. Since you are using Baseboard with copper tube/alum fin, you should have no problem getting return water to 140° within the first 5 minutes and the stack temperature should be 350° or more, without a problem. If you end up with Flue Gas Condensation you will notice water droplets that leak out the vent connector pipe and leave rust trails on the vent pipe in a few weeks. If you don't get that, you can leave the boiler operate at the reduced firing rate and save a little on fuel. If you do get the rust trails, then increase the fire rate to 1.1GPH by using a .90 GPH nozzle at 150 PSI.

Don't forget to paint the rust marks away with high heat aluminum or replace the vent connector pipe with new, so you can monitor for new rust streaks. You should be able to get the firing rate down enough so you can keep that oil boiler in operation for another 20 years. That will give you time to sack away enough for a new boiler later on.

katman

Thanks Ed. Here's the labels on the boiler:

Tankless coil has been disconnected and replaced with an indirect.

I installed a 1.10 60B nozzle, and set the pump to 140 psi.

I have a Carlin EZ-1HPW burner, so I would have to change the head bar if I go lower than a 1.10 nozzle.

With the 1.10 nozzle, I was originally using the Hydrostat 3250 Outdoor Reset. This led to the boiler only running for maybe 2-3 minutes since the high limit was typically only around 140-150 degrees. My stack temperatures got up to just around 350 degrees or so in the 2-3 minutes.

I disconnected the ODR, and set the high limit to 175, low limit to 135 and the differential to 30.
Once I did this, I could get a burner run time of 5-8 minutes as long as the thermostat stayed calling.
My stack temperatures also went up to around 420-450 degrees.

I did notice that I have the rust trails already on my vent pipes. However, they were there five years ago when I bought the house.

Here's my combustion readings with the 1.10 nozzle and the 30 differential:

Having thermal pre-purge enabled on the hydrostat 3250 seems to also help, as this stops the boiler from firing and instead purges the latent heat in the boiler thus saving on cycles. I had to enable this in the settings as it is turned off by default.

What's interesting is I just found the original service records, and it looks like this boiler was downfired with either a 1.00 and a 1.10 nozzle since new (strange since the head bar is a 1.10/1.25)

Do you think I should start off by trying a 1.00 60B nozzle, raise the pump pressure to 145 psi, and change the head bar to the .85/1.00 and see what kind of numbers I get or just go right for the .85 nozzle at 145 psi first?

Thanks!

mattmia2

If you don't have the tankless there is no reason to have it warm start, can set the low limit as low as it can go. 135 is a little low to keep it from condensing though oil can go lower than gas.

EdTheHeaterMan

@katman, The Aquastat that you have, may be the Original Equipment Manufacturer (OEM) specifically designed for WM. That control may not have the ability to operate as a WGO cold start boiler. If your system was originally installed with a WGO boiler and an indirect for DHW, then the control would automatically be set for cold start operation. All that said, since you are no longer using the Coil for DHW, there is no need to maintain any minimum temperature in the boiler when there is no call for heat of call for DHW. Set the control to the lowest temperature for LOW LIMIT as possible. If you can go as low as OFF that is the best setting for your situation. that will result in the lowest fuel usage. In the future, if you ever need to replace the Aquastat Control… Use the universal model that can be set to OFF in order to convert this WTGO to cold start operation like the WGO. Except for the tankless DHW coil, the WGO and WTGO are the same boiler in every other specification.

As far as setting up the burner to fire at 1 GPH with a .85 nozzle, that is where I would start and see if you get the minimum stack temperature of 350° within 5 minutes of cold start operation. If you do, then leave it there and look for signs of flue gas condensation on the vent connector, after several weeks of operating at this lower input. You may be in good shape.

katman

Hi, the original aquastat when it was a tankless was a Honeywell L8124A. This was changed to the hydrostat 3250 when the indirect was installed.

I can turn the low limit completely off on the 3250 - I kept it set to 135 because I thought it might be better for this boiler not to cold start it, and the gate valve on the balancing valve leaks water if the boiler temperature drops. I'm going to remove this balancing valve anyway. I'll also bump the high limit back up to 180 and keep the differential set to 30.

I'll change the head bar to a 1.00/.85 and try out the .85 nozzle at 145 psi and see what the readings are.

Do you guys think I should get a new circulator such as the Grundfos Alpha 15-58F and move it to the supply side along with the indirect circulator while I'm doing some of the piping work, or just keep the existing Taco 007 circulators on the return side?

Thanks.

EdTheHeaterMan

FYI:  If you originally had a WGO boiler of the same series, the OEM control would have been the L8148 aquastat.   You would not have the option to set a low limit with that control because there is no low limit.  Weil McLain does not see that maintaining  a minimum 135° on a cold start boiler has any advantage.  Their 66 and 68 series boilers also came with the L8148 aquastats and there are many of those 35 to 50 year old cold start boilers still operating across the country. The only advantage to maintaining 135°F in your boiler is to your fuel oil supplier.  They make more $$$ the more oil you burn. 

As far as repiping the boiler so the circulator pumps are located on the supply side of the boiler would be: if you are experiencing air problems. If you constantly need to purge air from your system (more that once a year) because you have no heat in a zone or a radiator resulting from air in the system, then you will gain an advantage in that repipe job, if designed correctly. Otherwise, if it ain't broke don't fix it. Lacking any air issues, there is no fuel savings or thermal efficiency to be gained my redesigning the pipes. The only advantage is to eliminate air problems.

mattmia2

tighten the packing on the gate valve so it stops leaking or add a little if tightening doesn't do it.