Downsizing nozzle on wtgo-4 and riello f5

7 year old post.

still good information

Close as I can guess, max firing rate on the 3 section is .95 GPH while the minimum firing rate on the 4 section is 1.00 GPH. What's .05 between friends? Especially when the actual firing rate can be +/- 10% at 100 psi from what the stamp says on the nozzle.

There's obviously more surface area on the fire side of the 4 section (even though it holds less water than the 3 section. Which is a little weird to me), so the pointy heads were probably worried about condensing flue gases at a lower rate.

FWIW, up until last month I had my WGTO-3 with a Riello F5, .60 nozzle at 150 psi for .75 GPH input for 24 years. The boiler ('96) was there when I bought in '02. It had an AFG originally. Rarely needed to be brushed. Stack temperature always around 420° gross. Now the whole thing is at the scrap yard.

When we bought this house, the WGTO 4 had a 1.0 GPH nozzle at 140 PSI delivering 1.2 GPH. The boiler rumbled and roared like a turbo jet and had a very high stack temp. I installed a .85 GPH nozzle and the correct head position bar for the Carlin EZ 1 burner. The boiler ran much quieter and the stack temp dropped significantly. But still, this setup is very much oversized for the size house we have. In the ideal world, I would like to get a Budereus G115WS-3 boiler but the payback is too long for us and the4 boiler has been discontinued by Bosch. My next step is to try a .75 GPH nozzle ,same angle and spray pattern and check that the stack temp is above 325 F ( is this a safe number or should it be higher ?)so I have no condensation issues and check the CO2 with an analyzer. If it does not work properly, I will back to the .85GPH nozzle. Any Comments?

I remember learning about oil burners in the latter half of the 1970s. Back then, there were a lot of large cast-iron boilers with lots of water content that were designed to burn coal. The nozzle size and other settings were done by the seat of our pants. There were some ratings on those old oversized boilers, like the Gross Input and Net Square Foot rating, but for the most part, we would pick a nozzle for the burner and take the stack temperature. If it was over 500°, we would use a smaller nozzle or put some firebricks in the flue passages to baffle the flue gas flow through the boiler. If the stack temperature was lower than 300°, we would install a larger firing-rate nozzle. The sweet spot was between 350° and 500°.

Condensation of flue gas on an oil-fired boiler just meant that you were sucking wet soot out of the boiler at the annual cleanout. Those cast-iron sections were thick and lasted forever. If you had the flue gas condensation problem, then the boiler failed after 40+ years of service. If it didn't have flue gas condensation problems, then the boiler lasted 50+ years. In either case, removing that coal boiler and replacing it with a modern packaged boiler always reduced the fuel consumption.

Often, those replacement boilers were also oversized, and that made for poor performance in many cases. When that happened, I would install a nozzle as low as 60% of the rated firing rate and see what the stack temperature was. If it was 350° or higher, I would leave it there and call it a success. Bottom line is, if you can get it to fire efficiently without flue gas condensation, then you have won the war against fuel waste.

Flue gas condensation is more of an issue with the smaller cast-iron boilers because of the low water content, so you need to make sure you get 135° return water within the first 10 minutes of run time and also have a stack temperature above 300° within the first 5 minutes of operation. If you get that, then you have won the battle.

Where you come to a problem is if there is an insurance company claim and you have made adjustments outside of the manufacturer's recommendations. If it ends up in front of a judge in a courtroom, the person who did not follow the specifications will pay the price. I was that person once, even though the problem happened 4 years after I sold the company and the new company made the mistake.

So, live and learn.

As far as the WTGO 3 and the WTGO 4 is concerned, there is a larger (or thicker) center section on that 3 boiler so it is about the same size combustion chamber as far as the firing rate is concerned, but there is less cast iron in those dimensions so there is more room for water. Looking at the parts list for the WGO-3. there is a different part number for that intermediate section, compared to the standard section on all the other larger sizes

When you look at all the configurations of the WTGO-3 Series 3 Gold boiler, you can fire it as high as 0.95 GPH and as low as 0.70 GPH. That is actually a little more than 20% less than the maximum—more like 26%.

If you happen to get one with a rating plate of WTGO-3LR with a firing rate of 0.70 GPH, you could actually fire it at 0.95 GPH, since Weil-McLain uses that same block of cast iron. However, since the rating plate says 0.70 GPH, you could leave yourself open to a liability issue.

What is stamped on the rating plate supersedes what you can actually do safely.

You might need to do this yourself. I installed an oversized boiler in a home once on purpose. The supply house had this boiler in the warehouse for over 8 years and marked it down so low that it was less expensive than the correct-size boiler.

I put it in and fired it at the proper firing rate for the load. This was new construction, and the job worked great for 8 years. I sold my business, and the technician for the new business owner read the label on the boiler and fired it at the proper nozzle size according to the boiler rating plate. I never left any information to the contrary, so the technician didn't think there was anything wrong with changing the nozzle size.

As a result of the confined-space dimensions for the larger firing rate, and the fact that I had also downsized the exhaust vent connector for the power vent, the burner sooted up the entire house.

The homeowner didn't sue the company that created the soot problem. They sued the company that installed it, and since I used my own name for my corporation name, and since the judge was a personal friend of the homeowner, I lost the case even though I was no longer in business and the company that sold the boiler to the customer had been sold to another business.

My insurance agent was smart enough to include completed operations coverage, and the insurance company paid for most of the damage, but I still needed to come up with $1,700 out of pocket.

The judge would not hear anything I had to say about the corporation that installed the job being separate from me personally. That is what can happen in a small town when you are not politically connected and your customer is.

So me telling your oil dealer to do something that got me in trouble is not going to happen. The fact that it will work just fine that way does not hold up in a court of law. And that is what your oil dealer has to look at.

I don't agree with this, without more data. Calling it 'good' because the stack temp is 350° isn't conclusive. What about excess air, draft, and CO? It's not hard to get any burner to run at 350 stack. The excess air could be 100% and CO could be in the hundreds…not good at all. If someone got sick or died, or some other disaster, you calling it good, will easily cost you in court.
And in the case of an AFG, you probably have the wrong end cone in there.
Downfiring, thinking you are saving oil, by sacrificing efficiency and ignoring manufacturer's specs is not the way to go. If you can't get a small enough boiler you need a buffer. Anything else is unprofessional. The late, great Jim Davis proved this over and over again with real world data.

@EdTheHeaterMan Thank you for sharing your hard-earned words of wisdom re downfiring. While I am not a heating pro, as a (now retired) mechanical engineer I also did some things professionally that were, in retrospect, probably not a good idea, but fortunately did not result in me being sued.

I would love to get a Testo and learn how to safely "do it myself," and as I have several years' worth of data on annual oil consumption vs. HDD's, I'm confident I could get good data on, say, a 60% downfired boiler (vs. our current 80%) and prove conclusively whether or not that increased our overall system efficiency. I'm rather surprised that such an important subject of debate (downfiring) has apparently impassioned experts arguing on both sides (some saying it increases efficiency, some saying it decreases efficiency), with apparently very little published data to back either conclusion.

Maybe the right answer is "it depends," as some experts seem to say that in their experience, downfiring has decreased the efficiency of the systems they downfired. @Jim Davis seems to be in that camp. While others say that in their experience, downfiring has increased efficiency. Is it possible both can be right, and the results depend on the particulars of the boiler in question? This debate sounds a bit like the proverbial blind men arguing about whether an elephant is like a tree (from feeling its legs) or like a rope (from feeling its tail).

Unfortunately my own experiments with our "elephant" will have to wait until next heating season.