Flue gas condensation- need input and suggestions

SuperTech

Long story, here's the short version. I was up on my roof tonight I. The dark around 7 PM and I got a chance to check out my chimney. My stomach sank when I saw how wet/damp the top of the chimney is. I looked down it not sure what to expect. I didn't notice it "raining" inside the chimney. It was hard to tell for sure but it appears that the moisture is more prevalent at end of the flue pipe where it's cooled by the chilly outdoor air.

I have done several combustion tests with three different nozzles last year, there was a thread I posted here at the time. I remember opinion of the community was mostly don't worry about it or just wait and see.

Details on my boiler which is still a work in progress. It came with the house but 90% of the piping is my work.

Peerless WBV-03
Beckett AFG with F4 head
Honeywell R7248U digital primary set up for interupted spark
Beckett 51771U electronic igniter
Clean cut pump, 15 second valve on delay, no post purge
Honeywell L7224U aquastat with outdoor reset controls matching Honeywell units
Tekmar 304V zone valve and circulator control, two zones going to add a third soon.
Main zone is cast iron baseboards, supply comes off the boiler 1-1/4" the at a Y becomes a 1" two pipe reverse return Venturi tee setup. Other zone is a 41 gallon amtrol
Circulator is a Taco Viridian VT2218. Pumping away from a Supervent micro bubble resorber. It's running on setpoint heat mode with boiler protection. This setting is supposed to prevent flue gas condensation. My setpoint temperature is 155 and the boiler protection is set for 135

I'm sorry for the long post. I need further technical training like Tim McIlwain teaches. All my coworker don't know, care or have crazy sounding opinions.

Is what I noticed intermittent condensation or a greater concern? What recommendations would you suggest? Larger nozzle? Higher oil pump pressure?Thermostatic bypass valve? Primary secondary piping?

By the way I'm piping in four nice big old cast iron radiatiors in a finished room in my basement soon, it's going to be in 3/4" on its own zone. How will higher water volume affect my system?What would you suggest to improve my setup while retaining the peerless WBV-03?

Also I've been driving myself crazy thinking about a Caleffi dirt mag. The price is close to the cost of my circulator, so I haven't bought it.
Has anyone else thought about home manufacturing of a removable device to catch magnetic particles? Or am I crazy? Is a dirt mag always necessary? I've never seen one installed in my 12 years experience.

SuperJ

With only one pump and no thermostatic bypass, it's going to be hard to do boiler protection properly. You need a way to decouple the load from the boiler and then gradually add it as the boiler comes up to temperature.

You could accomplish this with a thermostatic bypass, or other pumping/valve arrangements.

Keeping the VT2218 as a secondary pump (with closely space tee's), but adding a constant speed primary pump could work. You would put the return water temp sensor on the primary return line, and the swt sensor on the secondary line. If the return was cold the VT2218 would slow allowing the primary loop to recirc until it comes up to temperature.

You may have some funny interactions between your outdoor reset and pump, the hotter the boiler gets the slower the pump will run in setpoint mode (assuming it's on a fixed 155F SWT spt), this probably isn't what you want.

Personally I'm a fan of some sort of PS arrangement with constant circulation. If you do it right you can protect your boiler without sacrificing your hydronic balance.

SuperTech

@SuperJ thank you for your response! Your final paragraph is one of my concerns. I know both the VT2218 and the ODR are good things but might not work well together. But causing flue gas condensation while trying to eliminate it?

I was originally going to go primary secondary. The Viridian as the boiler pump and an Alpha 2 as the zone pump. But life got in the way and I never created a boiler loop. Now I'm worried it would look like hell if I try to squeeze one in. Everything would need be repiped.

Super J in your opinion do I have anything to gain from using any of the VT2218s modes? (Delta T) setpoint heat, setpoint cool or boiler protection

SuperJ

It's a neat pump, and it makes sense to use what you have. I'd probably use one of its modes as part of a boiler protection strategy. I'll have to think about, I'm going to bed.

SuperTech

Thank you. Can't sleep myself. Not because of the boiler, I'm not sure what I witnessed is an issue or not.

Still I'm always trying to figure out the best way to configure the settings on my system. I've read conflicting information online.

STEVEusaPA

When you were up on the roof at night, you didn't tell us why, did you happen to take the flue's temperature?
Also, are you showing signs of condensation in your flue pipe or heat exchanger?
I think your easiest option may be to switch out your aquastat for a Hydrolevel, and take advantage of circulator hold off below 140°.
I'd also ditch the outdoor reset, unless your piping primary/secondary, because it will cause short cycling. If it's set up at the standard 180° for design day, and 140° minimum, you are probably targeting 140° fall and spring, and will see much of the winter in the 150-165 range, which is quick for that boiler to go from 140 to 160.

What size nozzle are you running and what were the combustion results.

SuperTech

There was a thread on down firing my boiler but I can't find it. I tried a .85 80B, .75 and a .65 80B with the low fire baffle. I don't have my results with me but I usually aim for around 5.5% O2. The stack temperature even with the.65 nozzle measured over 425 if I remember correctly. I always maintain -,02" overfire draft and -.040--.05" at the breach.

I didn't have the opportunity to take temp readings last night

I haven't seen anything on the smoke pipe, I haven't had time to open up the boiler yet this year

hot_rod

Got a drawing or pic on how it is piped near the boiler?

There are some drawings floating around showing return protection with a bypass circulator in set point mode that may not, will not assure the condition you are seeing. The same for a single circulator installation if the circulator can not modulation down low enough.

What type of flue? Both the boiler and flue surfaces need to be kept above that dewpoint.

Does the ODR control have a boiler min setting, sensor on the return piping?

If you have time to watch, this webinar details the finer points of return temperature protection and flue gas condensation and some simple, appropriate piping fixes.

https://www.youtube.com/watch?v=hzPcVeSwwVU&list=PLuuV0ELkYb5VE0I4evUZ30b5U78CRlRdg&t=0s&index=71

STEVEusaPA

Hey @hot rod your drawing will flood the boiler. Both the water feed and the fast fill ball valve are open...lol. Just teasing you as I know it's probably hard to show the valve closed, and anyone would (should) figure it out pretty quickly

SuperTech

I do have some pictures from when I finished the zoning on the boiler. I'll attach them.
Flue is regular single wall smoke pipe, 6" I believe run to a masonry chimney. No liner.

The Honeywell ODR uses the sensor in the aquastat, only sensor needed for ODR is the outdoor one.

Thank you Bob!

Now just between the two of us, wouldn't it be possible with the right fittings, soldering, brazing and welding to make a device with a rare earth magnet that would collect ferrous debris like a dirt mag?
I'd like to get one but it's so expensive 😣

STEVEusaPA

Actually the .75 and below (I wouldn't do .65) show an F3 head.
That boiler fires best with the .90X80B Hago, F4 head. I know it's a PIA around here to get a Hago, so most people use a Delavan .85X80B, F4. I'd use that setup, and swap out the aquastat like I said earlier before I got into changing the piping.
This will keep you out of condensing on the fire side and the water side.
No set up mentions a low fire baffle.

SuperTech

I really like the idea of the thermal storage tank.

What would be a better improvement, adding a tank as Bob suggests or going primary secondary with the vt2218 on the boiler and an Alpha on the zones?

hot_rod

STEVEusaPA said:

Hey @hot rod your drawing will flood the boiler. Both the water feed and the fast fill ball valve are open...lol. Just teasing you as I know it's probably hard to show the valve closed, and anyone would (should) figure it out pretty quickly

good eye

SuperTech

I'm going to go back to the .85 80B nozzle today when I do my annual maintenance. Since I downfired my burner I have added an indirect and I'm about to add another zone with cast iron radiatiors. I'll take some pictures of the flue pipe and the inside of the chimney and look for evidence of condensation. Even if the stack temperature is hot enough in the breech to avoid condensation it doesn't mean that it's that same temperature where it exits the chimney right? I'm more concerned about avoiding chimney damage than saving a bit of oil with the smaller nozzle. I'll post pictures and combustion test results later this afternoon.

Thanks again for all the great input. I'm not really what I consider a super tech, but I'm working towards that goal everyday.

hot_rod

While we measure and react to condensation at the boiler return piping, with a sensor or probe into the pipe, it is actually the temperature of any metal or surfaces in the entire assembly. So the boiler surfaces as well as the flue surfaces. If the flue piping drops below that dew point anywhere along the distance you have the potential to condense.

You can observe this at the tailpipe of your truck, it will drip for the first few minutes when you cold start until the entire exhaust system warms above the condensing temperature.

There are other variables that predict where condensing will occur, your combustion analyzer will help narrow down the actual dew point.

STEVEusaPA

True, temperature at the breech will be much hotter than temperature exiting the chimney. You could climb up on the roof, European style, with a thermal imaging camera and shoot the temperature, just to be sure. If it's too cool at the top (or shows sign of damage from condensation, you next step is a stainless steel liner.
But let's see what happens when you open up the boiler and remove the flue pipe.

Jack

Also look at Appendix E in 31 for liner sizing. I've actually used 4" pellet vent as a liner and it worked perfectly. Back in about 95, Rich Krajewski, from Brookhaven, who did the App. E work, told me that the single best thing to do to improve chimney operation is to insulate the vent connector. Dura-vent and Selkirk models DVL and DS are good for that. The pH on your vent condensation is about 2.9. That is hot and it will eat the chimney. Portland cement is a lime based product so the condensate ends up being neutralized by the chimney. Look at all the leaning chimney tops as you drive around.

SuperTech

I just wrapped up my annual maintenance. I went back to the .85 80B nozzle. The boiler was pretty clean, it always is. I didn't notice any signs of condensate on the top of the boiler or in the flue pipe. I'll attach pictures.

I tried to get a good picture of the inside of the chimney, but it's not easy so I decided to clean out chimney base and see if I could find anything. I haven't opened it up in a few years.

Inside the base I found something unusual. The material in there was dark and damp. I found a couple of chunks of cement, but no pieces of clay tile thankfully. Is this from flue gas condensation?

The reason I was up on my roof last week was because I found it leaking in my attic. I also noticed that the flashing around my chimney is no longer sealed to it. Could this be a contributing factor? I'm going to have to replace my roof, the flashing will be sealed up then.

Check out the pics and please let me know what you suggest. I have also been looking into vent dampers, as much as I usually hate those things I would install one if it helps protect the chimney. Any thoughts on that would be greatly appreciated as well.

SuperTech

I forgot to post the results of the combustion analysis. I adjusted the barometric damper for an over fire draft of -.02", draft in the breech measured -.044".
Stack temperature 489 degrees, was 425 with the smaller nozzle.
5.4% O2
7 PPM CO, 9 PPM CO air free
32.4% excess air
11.66% CO2
83.8% efficiency
66 degree ambient temperature

I'd love to have a thermal imaging camera to check the chimney temperature, but that's one tool I don't own. I would go up on the roof and check temperature of the flue gases coming out but I'd probably break my neck thanks to the recent snowstorm.

hot_rod

This chart shows dew point #2 fuel oil at that CO2 level.

The crud in the pic sure looks like masonry product breakdown? Gritty feeling?

SuperTech

Thank you for the chart. It looks like at the CO2 levels I'm running I would be wise to keep the boiler above 120? Is cold start to blame? Perhaps my outdoor reset curve is wrong? Boiler protection on the VT2218 not cutting it?

The crud kinda felt like damp sand. I haven't seen it in the chimney base in any other chimney base I've cleaned out. I have seen a few that had chunks of the clay tiles in with all the soot. Those boilers had obvious combustion problems.

How would you proceed with this Hot Rod?

hot_rod

Sounds like two concerns, is the boiler running out of condensing mode quickly enough? It should run a good 10 minutes on every start to dry out completely. If it short cycles, it may not have enough fire time to get there? Or the SWT is too low on mild days, not able to get return above 120? A gauge and data logger at the return connection at the boiler would confirm that. Or a few hours of bucket time in front of the boiler.

Then the temperature in the flue also needs to get above condensing temperatures on every cycle, or at least dry out at some point each day.

Unless your ∆t circulator is piped to actually disconnect from the load, I don't see how it can assure 100% temperature protection on high mass or large water volume systems, especially with low SWT operation?

SuperTech

I have spent some time watching the boiler. I keep a chair nearby. I have tridicators on every supply and return and the circulator displays supply temp, return temp and GPM of flow. For boiler protection I have seen it slow down to 1 GPM until the return temp comes up.

I bumped up the thermostat one degree and I have been watching the cycle. The burner comes on when the boiler temp drops below 130, which is the boiler temperature low settings on the ODR. Burner shuts off around 145 with an outdoor temperature of 40.
The circulator is in setpoint heat mode with boiler protection, the boiler protection setting is 135 and heat setpoint is 155. During the cycle the return temp rarely dropped below 120

I become easily fascinated with new technology that I never see at work. I love getting new high tech components for my boiler and learning as much as possible about them. But it seems like either some of these components don't play well together or I don't have them set for optimal performance.

I bought this pump for the boiler protection mode. I'm very frustrated that it doesn't seem to work correctly. And I have spent countless hours reading about it online, but information is very limited. None of the other techs I know have any experience with this technology. Perhaps I made a bad choice. Taco should should let us know that the Viridian VT2218 doesn't work with ODR if this is the result.

Or it might have been the result of downfiring the burner in an attempt to gain efficiency.

hot_rod

One issue with VS for temperature protection is if the pump doesn't rev down low enough, I think that pump has the bottom of the curve locked out?

You'd be better off stoping that circ with a simple bang/ bang "neanderthal method" aquastat .

The earlier V/S cirs, the PSC style from Grundfos and Taco would go to 0. I think they both had tekmar boards on them, they were and still are $$.

That VT 2218 can and will work as a 100% return protection circ with proper piping, but I don't see it working as a single pump system?

Here are a few piping methods that do work. I have not tried the PAB valve method yet, but I tend to trust Siggy's numbers and calcs. I'm often the test bed for some of his off the wall ideas.

He gets the same questions about return protection piping and pumping not working adequately, hence all his doodling to find a good answer.

Not to say SOME bypass piped or bypassed pumped methods don't work, but it not hard or expensive to build a system that does let you sleep at night, we have the technology, used properly everyone wins.

SuperTech

Thank you so much for your help Hot Rod. I have been thinking a lot about primary secondary piping and usage of a storage tank. I have read about some of the advantages of that method. What determines the size of the storage tank? I have a good 40 gallon electric water heater tank not in use....

hot_rod

I’m a fan of buffer tanks. My shop 500 gallon tank buffers a row of thermal collectors and wood boiler, so I use it mainly as a flywheel.

The small 6 gallon buffer at the house is to better deal with the micro loads on the system.

In both cases they serve as my hydraulic separation P/S.

You can size for run and off times if you know the btu loads of all the zones you will run off it.

Here is a calculator to play with options.

https://www.lochinvaru.com/resource/calculator/buffer.html