Buderus GC144-5 producing a lot of condensate

chrisalecia

New Boiler: Buderus GC144-5 natural gas, (Input BTU/HR 132,500, 85% AFUE, 6”Flue). Also Logamatic 2107. 3 heating zones plus one DHW zone on separate circulator.

Old Boiler: American standard, Becket oil burner. 130,000 BTU. Unit was 38 years old at removal and still working strong. Same configuration as above.

Problem: Condensation in flue pipe (a lot). Buderus is exhausting into the existing flue (no liner)
I would mop up condensation in flue cleanout with paper towels to dry it (about a cup). Then overnight it would be full again with about a cup of condensate. This never happened with the oil burner. Buderus suggested that I increase the room temperature setting for both day and night setback to 78 F and see what happens in a week if condensate is still a problem.

My own theory – the new NG boiler is never reaching the stack temperatures that the oil boiler ran at.
Oil Boiler stack vent exited right out of the top of the boiler (no draft hood), and into the chimney flue. When the boiler was running it would get almost too hot to stand in the boiler room (approximately 6’ x 6’). If I kept the boiler room door open it would heat the whole basement space no problem. The new NG Boiler has a draft hood. When the boiler exhausts and the damper opens it also pulls in with it ambient room temperature further cooling the boiler exhaust. Also because the Buderus is a much more efficient running boiler – doesn’t run nearly as long as the oil Boiler did so the flue temperature never gets as hot as it used too.

I think I need a chimney liner. Buderus is saying one should not be needed and that there may be issues with the flue. Malarkey I say.

Tim McElwain

You need a liner simply because you have increased wet time with gas combustion and a much lower stack temperature will definetly cause this. What is the measured stack temperature along with other combustion readings taken with a Combustion Analyzer?

chrisalecia

I think I need a liner too however Buderus is amendment that the boiler can be vented into the existing flue. Also, My heating contractor says he has installed many Buderus units this way and never had an issue. I do not think a Combustion Analysis was done. My heating contractor has been in business for 30+ years and is probably going to fall back on that if I bring up an Analysis.

Even for a laymen I can see (and feel) that the stack temps are no where near what they were with the oil unit.

Ironman

The Stack temp is much lower because more heat is being extracted by the boiler and transferred to the water instead of going up your chimney.

Any, I repeat, any natural draft 80%+ appliance must have a liner due to the lower stack temps. The high mass of your cool chimney will cause condensation if not lined. If it's on an outside wall, then you need an insulated liner.

I'd like to know who at Buderus told you that it didn't need lining.

Just because your installer's been doing it for thirty years doesn't mean he's been doing it right. Sometimes, some of the older guys can be worst offenders because they refuse to learn the newer technology and want keep doing it the way they always have.

And, just to put that in context: I've been doing this for over forty years. And Tim McElwain has probably been doing it over sixty years. He's recognized as the top gas authority in this industry. I'd take his advice. He's right.

On a further note: the 2107 is a reset control that lowers the water temp as the outdoor temp gets warmer and vise versa. The more the water temp is lowered, the more efficient the boiler becomes and the lower the stack temp. Obviously, more condensation will be made. It's doubtful that the old boiler had any form of reset and probably ran 180* supply water. The Buderus can go as low 104* water temp.

chrisalecia

I'm with you guys and appreciate the advice very much. I've known my contractor for many years and trust his honesty. However I do agree on your comment on the old school guys and newer technology.

As far as who at Buderus I may never know. What confuses me more is that my contractor said when he called Buderus that the Buderus engineer implied there might be an issue with my flue. I don't know what to believe.

So, moving forward to solve this problem what is the recommended solution? By that I mean what's the best flue liner? Straight pipe or the flex pipe? Probably should still have a condensate drip tube as a backup also no?

Ironman

I wouldn't say any one brand is the best, but I would recommend spending the extra $$ for a stainless steel liner over an aluminum one. The aluminum ones don't seem to hold up as well.

icesailor

Remember, although stainless steel may cost more, it is a terrible electrical or heat transfer medium. You don't see stainless steel wire on overhead transmission lines, but you do see aluminum wire.

Because stainless steel is such a terrible heat transfer medium and has such superior corrosion resistance, it should be the vent liner of choice. Because it will loose so little heat to the cold.

In the 1960's, 1970's, the Stainless Steel Manufacturers decided to take over the copper tube market with stainless steel tubing. The plumbing codes strenuously resisted. The heating industry welcomed it with open arms. It was extremely difficult to solder, even for experienced solder's. It used standard brass fittings on the SS tube. The SS tube was such a poor conductor of heat that you could hold your hand 3" away from where you were soldering and the tube wouldn't be hot. Or barely warmer than your hand. Most that leaked were leaking where the heat wasn't applied. Nasty stuff. I'd hate to see the MAPP gas flame thrower crowd facing THAT battle. It was hard enough for we with Air/Acetylene Prestolite torches. A #3 tip was more than adequate, and you could bet all around the fitting without burning the wall.

I wouldn't get nuts trying to insulate between the liner and the masonry. Air is an excellent insulator. If the SS liner is sized properly and I mean "Properly", it should work fine. I'm not going to say that it will make a 3 sided chimney correct. That is a code issue.

Robert O'Brien

GC144/5 and 2107? This is not a factory pairing,how is it mounted?

chrisalecia

Mounted on top like usual. Single circuit w/DHW. Day Night curve with outdoor reset. It is wired to work with the Aquasmart.

R Mannino

Two wells? I can understand how to wire them together, but it's redundant and the Aquasmart isn't necessary or vice versa. With only one heating zone get the BFU and be done with it.

Robert O'Brien

No provision to mount a 2107 on a GC series boiler?

chrisalecia

2107 was mounted on top. My heating contractor said the aqua smart was still needed and works with the logamatic. He mentioned to me why but I can't remember. The house has 3 zone valves but the 2107 is programmed for 1 circuit since the home is not using remote controls and is using thermostats to control the zone valves. So if any one zone valve calls for heat the single circuit activates.

Bear with my limited knowledge on the system. By the way for the other advice I received earlier. The Buderus tech support said I definitely need a liner. It was the local sales rep that initially said I didn't from his experience. Then after learning more about the conditions he changed his opinion and recommended a liner.

unclejohn

In the Buderus brochure on page 6 it says " conventional chimney venting " It also says not suitable for logamatic controls. Get the return water temp above 140*f and your problem should go away. Not that a liner would be a bad thing I would also run a new flue without the clean out, also did you leave the barometric damper in the flue?

chrisalecia

unclejohn said:

In the Buderus brochure on page 6 it says " conventional chimney venting " It also says not suitable for logamatic controls. Get the return water temp above 140*f and your problem should go away. Not that a liner would be a bad thing I would also run a new flue without the clean out, also did you leave the barometric damper in the flue?

Man, nice find. I didn't even see that. I'll have to ask about the GC144 being compatible with the Logamatic. I wonder if the Logamatic and Aquasmart are in conflict with each other. How do I get the return water temp to 140* and is that a good idea? How would it effect the efficiency of the boiler? We used the vent damper / draft hood that came stock on the GC144.

unclejohn

The logamatic is outdoor reset and may have some other functions. You have a cast iron boiler and do not want to run low water temps on that boiler.

chrisalecia

unclejohn said:

The logamatic is outdoor reset and may have some other functions. You have a cast iron boiler and do not want to run low water temps on that boiler.

But how can that be if the Logamatic can be used on a G124? The GC144 replaced the G124. Though I do agree that it looks like lower boiler temps are one of the issues. However, today was 26* in the morning and it's now 35*. If the outdoor reset from the Logamatic is not active because of the winter temps, why am I still getting condensation?

I must say it's driving me nuts.

Robert O'Brien

The logamatic isn't for use on the GC124 either! The GC series is a USA only product.

chrisalecia

Sorry I meant the G124X. This is no longer offered. The GC144 is the new one. Looking at the literature it looks like the Logamatic is compatible with the 124 but not the 144 as Robert found. Another fact I uncovered today from the Aquasmart manual is that the Aquasmart has a low water temp limit of 140*. The Logamatic runs well below that.

unclejohn

This should be no mystery. It's a CAST IRON boiler. It's low limit is 140*f

Robert O'Brien

Wrong again! The GC144 is the new version of GC124 not G124, in fact other than the name there is no difference between the GC124 and GC144.

chrisalecia

The original model spec'd for my job was a G124x like this one:

http://www.buderus.us/files/201001230141030.G124-234-334X.pdf

The brochure shows the use of a Logamatic as an option which as you pointed out is not the case on the 144. My contractor states he has installed many Logamatics on the G124x model.

The Logamatic will run the boiler at lower temps especially during outdoor reset. So, either I'm reading wrong or I'm totally off course.

Am I driving you guys nuts yet?

R Mannino

chrisalecia said:

Am I driving you guys nuts yet?

No it's starting to make sense now.

You need a liner.

chrisalecia

R Mannino said:

chrisalecia said:

Am I driving you guys nuts yet?

No it's starting to make sense now.

You need a liner.

OK, since your still with me, consider this.

The 2107 was put on the GC144. I find out after the fact that the Buderus brochure says its not compatible. The 2107 has the boiler firing at lower temps at times sometimes with a low temp of 120*. This may/may not be the cause of my condensation problem. If the Aquasmart was running the boiler as originally configured, the low temp setting would be 140* causing the boiler to fire more often, run hotter.

So, am I installing a liner to just support the Logamatic? Meaning if I took it off and just ran the Aquasmart would the system run as designed and not cause condensate issues?

If so I would be spending some considerable money in order to save a little in energy costs.

Jack

If this combination has, so far, been condensing you can increase the water temps and hope that it does not condense. The thing is, every flue condenses. As Tim pointed out you are getting a greater "wet time" with your new system. wT is the period where the flue is getting instantaneous condensation. System and flue design should be selected to minimize WT, meaning that the flue should heat up and dry off quickly. Condensation is exacerbated by oversizing. You replaced a big old boiler with a new big boiler. I wonder how oversized it is. You can bump the water temp up and it will likely help, but heating season is long where you are and conditions change regularly & constantly. Put in the SS liner and sleep better nights. Otherwise, this is one of those things that will kinda sit on your shoulder every time you walk by the boiler or hear it fire up. Hmmm, I wonder how my flue and new boiler are doing?

Ironman

I checked with my Buderus rep who's just about the smartest hydronic guy I know and who also knows the 2107 better than anyone on this side of the ocean and can tell you how to service and program it while he's in traffic on I95. Here's his line: the GC 144 is made from the exact same GL-180M cast iron used in all their cast iron boilers. Your boiler sections are the same as their other gas models. The only difference is the GC144's been re-arranged to be an easier replacement for the American market and it's cabinet is narrower. Because of the narrower cabinet not having the pre-notched holes for mounting the 2107, Buderus does not list it as an option for the GC144. That's the only reason. There's no technical reason.
He told me he has his contractors use it with the GC144 all the time. The only issue is creating the mounting. There's no warranty or technical issue.
He further told me that he's had this discussion with the factory on several occasions and their reasoning for not listing it was the mounting and they didn't think that many who purchase the GC 144 would be interested in a high end control like the 2107.
You still need the aqua smart control, but it needs to set to allow the high and low parameters of the 2107.
The difference in efficiency that the 2107 will make in the milder shoulder seasons is substantial.

chrisalecia

Hey Bob I wonder if your rep is my rep (Rich?). If it is the same guy he has helped me substantially and answered all of my questions. I called Buderus this morning and got the same answer on mounting the 2107. Thank you very much for chasing down my questions - that's just awesome.

My heating contractor is going to take some stack temp readings to make sure the unit is firing at spec. If so, I'll be installing a SS liner.

I know I beat this one to death but I'm glad I did because I learned a lot and learned there are some very knowledgeable tradesmen out there that still take pride in craftsmanship. I myself of course can talk about this kind of stuff forever. I owe a round of beers for sure!

Ironman

Glad you're getting everything worked out.
Roy Hall is my rep. He does the mid Atlantic area.

unclejohn

The 124 was for the US market only, and now the 144 is for the US and Canada as well. One boiler for North America. Now it's true that the reason they do not recommend that control is the mounting and it can be remotely mounted and wired. But a good reason not to use that logamatic control is because it's a cast iron boiler, running water temps below 140 will cause condensing inside the boiler as well in the flue.

chrisalecia

As I start to peel away the layers I find out more. One comment from above mentioned my new boiler might be oversized. Can you guys please recommend a good heat loss calculator? I've searched online and there is definitely a lot of them. Slant Finn has a pretty detailed one that you can download to your smartphone. I'd like to know what the experts recommend.

In my OCD way I would like to know how oversized I am. I have hydronic baseboard and an indirect 40 Gal. DHW tank.

Ironman

SlantFin is the one we generally recommend.

chrisalecia

So, here's my numbers:

Equation #1
155LF hot water baseboard
155' x 560 = 86,800 Btuh/hr

Equation #2
Slant Fin heat loss calculator 37921 based on 70* interior 10* exterior.

Remember I also have an indirect DHW

What boiler size do I need?

Ironman

How many square feet is your house?

chrisalecia

2400 sqft

Ironman

Is your house newer or older construction? How well insulated and sealed? One story or two?

chrisalecia

1976. Two story colonial. Replacement windows, reinsulated the attic. Wall insulation is original. Finished basement. Ext doors are new. Original cedar siding. New garage door keeps no lower than 50*. Even though the windows are replacements and I did spray foam, they are still drafty.

Ironman

Are you including the basement or garage in the 2400 sq. ft?

chrisalecia

Basement yes, garage no

SWEI

chrisalecia said:

Slant Fin heat loss calculator 37921 based on 70* interior 10* exterior.
...
What boiler size do I need?

37,921 BTU/hr at an 86% efficiency would need a firing rate of 44,094 BTU/hr.

I also have an indirect DHW

What size is the indirect? What kind of DHW loads do you have? Even the smallest GC144 (74k) will give you roughly twice the recovery rate of a standard gas water heater.

Ironman

Your calc seems a little on the light side. I would think 55-60k btu's would be closer.
The 560 btu pr. ft. of baseboard is with 180*water entering the baseboard. A system with 180* supply and 160* return has an average water temp of 170* and 500 btu's per ft. of BB is the number to use. So, that would indicate that your BB is sized for 77.5k btu's.
This is a good thing since over-sizing the BB allows for lower water temps which means higher efficiency. The negative side is that it also means lower stack temps and greater likely hood of condensation.
An over-sized boiler will short cycle and that can cause excessive condensation also.

Did you contractor do a heat loss calc? It looks as though he just sized it off the old boiler.

chrisalecia

40 gal boilermate. 3 showers in the morning. Boiler is rated at 85% non condensing. I mentioned what was installed in the original post. I'll take all opinions.

Ironman

Opinions? There're like armpits: everybody has a couple of them and quite often they stink.

Personally, I would have gone a size smaller on the boiler and up-sized the indirect. But that's my opinion.

The 2107 is not an on-demand, cold start control. It maintains a warm boiler, so that helps reduce condensation.

Get the chimney lined and your problems will go away.