Boiler replacement question: Two staged boilers setup vs one large with a 2 stage gas valve

George3

I am a Denver homeowner with a large two pipe steam system - Well McLain(EGH-85 349K BTU Input) boiler, 10 various sized convectors and 5 big radiators. The system operates at 8-12 Oz of pressure controlled by Vapourstat. The boiler is about 15 years old and last April started leaking between the sections. Currently we are deciding how to best replace it.

In the winter half of the radiators/convectors are turned off as we don’t use the rooms. That in turn makes the boiler to shortcycle(5-10 min) which creates uncomfortable heating. The aim is to have replacement boiler/boilers that can handle varying heating requirements better. The EDR survey was done - 980 sq.ft EDR. Adding the pickup factor(x1.33) and 5500ft altitude correction(20%) it was determined we need a boiler/s with an input of over 450k BTU. Since the old 349K BTU boiler was heating the house with all radiators on pretty well I think the 450K BTU is too much and that max of 400K BTU total input should be sufficient.

After that overture I would like to ask for your expert opinions what boiler setup is best under my circumstances – one large 400K Btu boiler with added 2 stage gas valve or 2 smaller ones (60/40) staged by vapourstat with possibly 2 stage valve on the bigger boiler? The smaller boilers will just fit trough my narrow boiler room door while the big one needs to come disassembled.

My installer prefers Peerless and the local rep told him that the warranty of the boiler will be voided if retrofitted with a 2 stage gas valve as it doesn’t come as an option on smaller steam boilers. Since the 2 boiler setup will cost 50% more is it really worth and what are the advantages?

I would appreciate your help.

jumper

One boiler is simpler. Regarding water level and regarding stacks. If 350K suffices now why go any higher? Why not go even less and augment with a bit of electricity?

nicholas bonham-carter

First try and determine why the boiler has failed so early. I would have expected twice the life from that boiler.
If there has been a leak from the returns, then an automatic water-feeder may have been adding fresh water constantly, with too much oxygen in the water.
Boiler pro has written articles here about systems such as yours, which have been sized to the building heat-loss, instead of the radiation, with success.
My preference would be the two boiler setup, piped into a common, large header, using Gifford (instead of Hartford) loops.
I am surprised that Peerless would be against using a two-staged gas valve, as they offer that option on their larger 211A series (Mod-U-Pack). The smaller peerless boilers also have the advantage of using metal connections between the sections, instead of the rubber gaskets used on the larger boilers.--NBC

KC_Jones

@vaporvac has a twinned boiler setup in her house on a system half again as big as yours and she could comment about how well it works for her. Do you know what type of system you have? I will reiterate that is an extremely short life for that boiler and you should do a system wide evaluation as to why it failed so soon. Leaks would be the first thing to look for. If you do have an automatic feeder and you add a new one, make sure you get one with a digital water meter to track water usage. These boilers should last 30+ years with proper care.

JStar

I've done a bunch of these twin systems. I can help you and your contractor out with anything you need to know. If two stages is good, four is even better! On a two-pipe system, staging is a no brainer. It should be mandatory.

As for the warranty issue, wouldn't Peerless need to prove that the GCV's caused damage?

George3

Thank you all for your suggestions!
When my current boiler was installed 15 years ago all the near boiler piping was done wrong and on top of that it was all done in copper. In 2011 I posted on The Wall looking for knowledgeable contractor in Denver to fix it:

http://www.heatinghelp.com/forum-thread/137103/Need-help-in-Denver-Co#p1274070

Dave Stroman did a good job re-piping it and removed unneeded condensate tank. Digital water meter was installed to track water usage. In the last couple of years I did notice high water usage but assumed it is normal since there was no leak anywhere and there are no buried pipes.
It started leaking on the floor only after the boiler started cooling down in the spring. I removed the insulation at the back of the boiler and saw the leak between the sections below the water lever. It must have leaked for a while (quite corroded) but insulation probably absorbed the moisture and it evaporated when the boiler was heating. When I topped it up and started the boiler I could not see the leak as probably the hot sections expended and if it was leaking a bit it would have evaporated on the surface of the hot boiler fast enough to not drip. When it cooled down it started leaking again since the automatic water feeder was trying to maintain the water level. That is probably why the water feeder usage was high lately.
The expanding former copper piping (for more than 10 years) might have damaged the cast iron boiler and shortened its lifespan.
I cannot identify the exact type of my system since the original boiler and piping was replaced when the current boiler was installed by the previous owner. Back in the 1930s most of the cast iron radiators were "upgraded" to convectors.
I lean towards the 2 staged boiler setup (also suggested by the Peerless rep) but unless I have 2 stage gas valve on at least one of the boilers to make the system with 3 or 4 stages I can’t see its benefits to justify the much higher cost and complicated piping.

George3

Joe, thank you for offering your help on twin systems! I will mention that to my contractor if we go that route.

nicholas bonham-carter

With a two boiler setup, you have the stages you need, without either one having a staged gas valve.
When the thermostat calls for heat, both boilers will fire. When the pressure reaches a couple of ounces, the lag boiler will be cut off by the vaporstat, leaving the lead boiler to continue firing until the thermostat is satisfied. Calculate the EDR of your radiatiors, and separate them into groups, of always on, and sometimes on, and post here. The sizing of these boilers is key to the success of the system.--NBC

ChrisJ

My system is only 392sqft worth of radiation on a single pipe system and the thought of two 62,000 btu boilers has crossed my mind a few times.

For something the size of yours I'd say it's a no brain.

George3

Nicholas, the total EDF of my system is 990 =415(occasional use)+575(always on).

The Steam Whisperer

I find it very common for the EG/EGH and LGB to start leaking on steam around 14 to 15 year. I have heard through clients that one of their largest installers says that this is the expected life of the boiler. They often fail at the plastic section gaskets, but sometimes rot out due to excessive make up water.
Before replacing the boiler, I would figure out your heatloss for the home. With those btu capacities, I am heating a 10,000 sq ft home in Chicago that has about 60 radiators.

If your heat loss is much lower than your radiation capacity, then you can orifice the supply valves to reduce radiation load and then size the boiler to heatloss.

2 boilers provides back up, however, if you use a modulating burner or two stage in a single boiler, you will probably have better efficiency. Also, with two boilers, you typically have to isolate the second boiler when it is not needed, or install a spill trap to prevent it from becoming overfilled and then deal with the additional jacket and flue losses of a hot boiler that is not in use.

With two stage and orificed supply valves, you could simply use a two stage thermostat, or with modulation, a single thermostat with outdoor reset of the flame size.

jumper

Seems times have changed. Used to be an advantage of multiple boilers that you eliminated the power burner. But like I said there were flue issues or jacket losses. Also you had to plan how water level would be controlled. A superintendent could soon learn how many boilers to operate according to weather.But does George3 want to mess around each day?

JStar

A simple and readily available two-stage thermostat acts as a basic indoor-reset controller. No human action needed. I've never had a single water issue with multiple boilers...unless they were installed by somebody else.

Dave Stroman

Hello All. I am the one who fixed up George's boiler a few years ago and got it working again.
I think the question that keep coming up with my discussions the Geo is how low can that two stage valve be adjusted? If 3.5" is normal at full fire, what should that low fire pressure be adjusted to?

JStar

It's usually in the 1.5"WC range and can't be adjusted. Well, it can be, but not safely.

Dave in QCA

One thing worth noting on the EGH boilers, about 2 years ago Weil-McLain upgraded this boiler from series 4 to series 5. I'm not sure of all of the changes, but I am aware of 2 specific items. First, they lowered the firing rate by 10%. Second, they add baffles that slip down between the sections in the flue passages. These changes and perhaps other resulted in and increase in efficiency to 82.3-82.5%. I can't find the old efficiency, but I think I recall it was 80%, or perhaps 81% at the most.
With the firing rate turned down, it would also seem that the stresses on the boiler would be decreased and longevity increase.

ChrisJ

Dave in QCA said:

One thing worth noting on the EGH boilers, about 2 years ago Weil-McLain upgraded this boiler from series 4 to series 5. I'm not sure of all of the changes, but I am aware of 2 specific items. First, they lowered the firing rate by 10%. Second, they add baffles that slip down between the sections in the flue passages. These changes and perhaps other resulted in and increase in efficiency to 82.3-82.5%. I can't find the old efficiency, but I think I recall it was 80%, or perhaps 81% at the most.
With the firing rate turned down, it would also seem that the stresses on the boiler would be decreased and longevity increase.

My 2011 EG series with damper is rated 82.9%.
Do you have a picture of these baffles or know if they can be bought?

JStar

ChrisJ said:

Dave in QCA said:

One thing worth noting on the EGH boilers, about 2 years ago Weil-McLain upgraded this boiler from series 4 to series 5. I'm not sure of all of the changes, but I am aware of 2 specific items. First, they lowered the firing rate by 10%. Second, they add baffles that slip down between the sections in the flue passages. These changes and perhaps other resulted in and increase in efficiency to 82.3-82.5%. I can't find the old efficiency, but I think I recall it was 80%, or perhaps 81% at the most.
With the firing rate turned down, it would also seem that the stresses on the boiler would be decreased and longevity increase.

My 2011 EG series with damper is rated 82.9%.
Do you have a picture of these baffles or know if they can be bought?

I've made them before. I don't suppose you would want a few...???

ChrisJ

JStar said:

ChrisJ said:

Dave in QCA said:

One thing worth noting on the EGH boilers, about 2 years ago Weil-McLain upgraded this boiler from series 4 to series 5. I'm not sure of all of the changes, but I am aware of 2 specific items. First, they lowered the firing rate by 10%. Second, they add baffles that slip down between the sections in the flue passages. These changes and perhaps other resulted in and increase in efficiency to 82.3-82.5%. I can't find the old efficiency, but I think I recall it was 80%, or perhaps 81% at the most.
With the firing rate turned down, it would also seem that the stresses on the boiler would be decreased and longevity increase.

My 2011 EG series with damper is rated 82.9%.
Do you have a picture of these baffles or know if they can be bought?

I've made them before. I don't suppose you would want a few...???

Think it would help? I'd need 3 I think?

Dave in QCA

http://www.weil-mclain.com/en/assets/pdf/550-142-782_1112.pdf
Look on page 37. Page 10 also shows installation of the baffles and indicates they are on EGH only.

Because the EGH is a commercial boiler, that is, over 300,000 BTU firing rate, it is rated differently.

The EG ratings are SEER and the EGH ratings are combustion efficiency. Generally the combustion efficiency would be a lower number (I think). EGH usually does not have a damper. Standby losses up the flue are not included in the ratings.

Dave in QCA

BTW...... I have a spare, little used, Honeywell, 1.25" 2-stage diaphragm regulating gas valve.