Condensing Modulating Gas Boiler Questions

[pamike]

I recently installed a Condensing Modulating Gas Boiler for my new radiant floor heat. I have a few questions for the experts.

-I turned down the max BTU output on my boiler because I was having temp overshoot. How does the boiler limit the max btu? Is the boiler still efficient when running at less than max btu?

-I don't have a floor drain close to the boiler. Any pointers on what to do with the condensate line? It produces a lot of liquid

-Can someone explain how the outside temp sensor changes the boiler operation. Does it not fire the water as hot? Or not as fast?? The boiler hits the temp point, it appears, no matter what the temp is outside

Thanks!

 

[LS6 Tommy]

Sounds like the outdoor setback schedule is either not set correctly or the controller isn't working properly. The condensate has to be neutralized by code, and in many places it can't drain to the outside, it has to be indirectly drained to a waste line.

Do you have access to an electronic copy of the manual that you could post?

Tommy

 

[pamike]

https://files.gitshare.io/link/nG2-Y8bSGCA/K2WTC Combi I&O Manual.pdf

Here is a link to the boiler. Its a U.S boiler, 180k combi unit.

My "pro" installer was having issues and couldn't get the system up and running so I took over. The outdoor sensor is installed and wired in, but I am not sure what exactly the outside sensor is called in the manual...

 

[acmikee]

condensate can be pumped to a drain or out side using a little giant pump but you first have to run it thru a neutralizer
the outside are sensor is for resetting the boiler temp..so as outside air goes down boiler temp will go up depending on reset ratio

 

[pamike]

condensate can be pumped to a drain or out side using a little giant pump but you first have to run it thru a neutralizer
the outside are sensor is for resetting the boiler temp..so as outside air goes down boiler temp will go up depending on reset ratio

Can you point me to a neutralizer? Never heard of such a thing...

I am a little perplexed by your reset ratio comment. The max temp they say to run radiant through concrete is in the 110-120 range. I set the boiler max at 120. So that will be the max and the boiler temp will go lower than that as its gets warmer outside?

 

[Chris705]

Look at page 104 for a description of outside air set point.

 

[Jackfre]

Wow! That manual reads like freakin' "War & Peace." Only 66 pages of venting instructions. There is a lot "in" that boiler to understand. The ODR system will, when enabled, adjust that output temp of the boiler depending upon outdoor temperature. Make sure that sensor is on the N side of the house and not in direct sunlight. Running a radiant system your max supply temp to the slab should be not over 120*. The ODR system will provide cooler temps as the outdoor temps go up and hotter water as the temps decline. It appears, and I only scanned the manual that there is a lot for you to digest here. You can make the system sing about any song you want it to, but you have to be really squared away to do so. How is this boiler piped? Is it primary-secondary or direct heating as they show. If it is direct they have some very pricey and large circs (0011/13)? Do you have pex-a/oxygen barrier pex? If not you have to isolate the slab from the heat loop with a HX. That is non-negotiable. Failure to do so could require a new boiler in about 2 yrs...or less. Are you hitting the minimum flow rates (pg73) for the boiler (9.3-13.3gpm)? Is it LP? Was it properly converted?
Having freed your "Pro" frankly, you are in a fix. You need to be on the Tech line to the manuf, but they, correctly, would be within their rights to tell you they will speak only to the pro. Keep in mind that the phone tech can only see what you tell him you see. Get the pro back in and make the call to the tech line on speaker and let them walk you through the set-up. Prior to doing so, take the manual and carefully trace your piping lay-out so you know what has been done. Ask the contractor any questions that vary from the manual.
Generally, I tell people to pump or drain the condensate over to the neighbors tomato garden. They like acidity and the pH on the condensate is around 3.2. That is hot. Do not drill a hole in the slab and let it drain. It WILL eat the slab from the bottom up. I have seen it. Tommy is, as usual, correct on the condensate neutralization. I only scanned the manual. By the time I got to page 100 I thought I was getting one of those flash-back they promised me from my psychedelic days, so I am not an authority on your ODR system. Report back!

 

[LS6 Tommy]

I have used Neutrasafe brand and like them, but any decent refillable model is fine. You can get them at plumbing or HVAC supply houses, amazon, online dealers. They are sized by boiler Btu and you need to replace the media annually.

https://neutrasafe.com/product-overview/

Tommy

 

[pamike]

Good thing I didn't listen to my "pro" that said to drill a hole in the slab and dump the condensate down there...

Jackre, The boiler is up and running, I just don't think its tuned in to optimum performance. Yes, the outside sensor is tucked up under the eaves. Not in direct sun. I understand your comment about boiler temp adjusting with outside temp, but I think in the manual the boiler will adjust temps from 180 down to 130. We are already below that min at 120...
The boiler is plumped up direct. No primary/secondary loop. I have enough flow. When the "pro" had the supply manifold plumbed in backwards and the flowmeters were blocking flow the flow sensor in the boiler was tripping out..thats squared away now with proper plumbing. Yes, I used oxygen barrier pex. I installed that myself. Boiler was converted to LP by me. "Pro" forgot to do that and kit was laying in the box....
I think I answered all your questions.
My big remaining question is will the boiler adjust the temp since I am already down below the range of temp adjustment? Or at least that's how I read the chart...

 

[Jackfre]

If you are running strictly radiant 130 is to high and should be mixed down. There are a number of ODR products out there and I don't work with the them daily so I don't know all the ins and outs of each set-up. Some are a real pain to understand and then the process of programming can be challenging (face to the right, hop up and down on your rt leg three times and only then with your left hand push the second button from the top on the left bank, two times). As you are the pro call tech service and have them walk you through this. I have not read your entire manual. I only scanned it, but there should be different Set-points in the ODR for the type of heat. For instance, the boiler I am most familiar with had four temp set points depending upon the type of distribution. Baseboard ran at 180, air handlers at 140 or 160 an radiant a max of 120 and they all adjusted down from those high points based upon outdoor temp. I think that if there aren't these broader set point adjustments that tech service will suggest a repipe to primary secondary. At the least, you may want to install a tempering valve in the radiant supply to control the slab input temp.

 

[Radix2]

Here are the things you need to keep in mind.

1. The lower the return water temperature, the higher the boiler efficiency - this why you want to use outside reset and minimize the output temperatures. At temps above 140 most of these condensing boilers won't condense and efficiency falls way down. To get your rated 95% or whatever, typically you need to be below 115deg. Bottom line, the lower the return temp to the boiler, the more efficient it is.

2. I'd be surprised if your minimum output temp is 120 for outdoor reset, maybe there are different settings you need to get to. It will take dome trial and error to find how low you can go, but it would be common to need only 80 or 90 degree water to keep the place warm in chilly spring or fall weather the only time 120 should be needed is when it very cold outside if the system is properly designed.

 

[pamike]

I am confused by the comment that 130 is too high and should be mixed down. You wouldn't set the boiler at say 120 to 130 and run it right into the slab loops? You would set boiler higher and mix the water down to temp??
Update: I spent a lot of time reading and studying the manual and it looks like I can set the minimum boiler water output temp to 80 degrees and the max output at 120. The boiler will then adjust between those temperature ranges depending on the outside temperature. Is there any danger with having the boiler output temperature that low? I read somewhere about 140 being the ideal boiler output so that condensation doesn't corrode the boiler??? Or is that only with non condensing boilers?

 

[66HertzClone]

Since there is an going discussion here about these units, Id like to ask some questions. I am in the process of purchasing a 1900 sq foot ranch style home, full basement. Currently has an oil fired combi unit for heating and DHW, during the home inspection it was found that it is leaking, has been for a while given the stains and the fact that he has a hose connected to bleed out the air, this has been in place during each of my three visits to the property. The boiler appears to be the original unit given the lack of modifications to the piping for it, so it is about 40 years old, end of it's life I have been told.

I would like to have gas as a fuel, it is out on the street, the range is all electric as is the dryer, both of which I'd prefer to have gas at least for the cooktop and dryer at some point. I have a grill that is fueled with natural gas, a Weber brand grill which I understand frowns upon conversions, the house is wired for a backup generator, so adding a transfer switch and a standby generator might also happen in the future. Seems like a good time to convert, pull the oil boiler and the oil tank, have a new high efficiency combi unit installed to replace it, taking advantage of the current state and utility rebates available. Convince the current owner to provide some discount to the price of the house and pay for the difference out of pocket.

There is a well for the water supply, I don't have the results of the water test yet but no doubt the water will be rather hard as there are at least three things in the basement that are part of a water softener system. Can any of you provide some sort of recommendations on what brand, model number of combi units I should consider? The house is in Morris county NJ, so a unit that is familiar with local contractors I think would be best.

Thanks for any help or direction you guys can provide with this.

 

[Radix2]

I am confused by the comment that 130 is too high and should be mixed down. You wouldn't set the boiler at say 120 to 130 and run it right into the slab loops? You would set boiler higher and mix the water down to temp??
Update: I spent a lot of time reading and studying the manual and it looks like I can set the minimum boiler water output temp to 80 degrees and the max output at 120. The boiler will then adjust between those temperature ranges depending on the outside temperature. Is there any danger with having the boiler output temperature that low? I read somewhere about 140 being the ideal boiler output so that condensation doesn't corrode the boiler??? Or is that only with non condensing boilers?

You should not need any mixing with your boiler, it should be able to control the temp properly for the floor loops, mixing is used with noncondensing boilers.

To attain your high efficiency, you must operate at low temperatures, the lower the better (higher the efficiency). No problem at all going down to 80.

Non condensing boilers need high return temps to protect the boiler - does not apply to you.

 

[Lonnies Performance]

My calculations said I don't need over 102 deg water at 0degF.

Try setting your OA temp reset to range from 80 to approx 100 & see how it works.
If it doesn't keep up on the coldest days, raise the upper temp limit.

Start conservative & you will have the most efficiency.

As for pri/sec systems, you can also use them with a condensing boiler if you want to further lower the temp below the boiler low limit setpoint. I'm currently doing this as my boiler low limit is 86 & I can lower the secondary supply temp to below 80. By reducing the primary flow (variable speed pumps) and/or increasing the secondary flow will cause more return water to mix back into the secondary loop.