Natural gas hydronic boiler condensing concerns

kfCT1

I have a 4,000 sf home in CT from 1931with a 250K BTU cast iron boiler (Utica installed around 1983) piped to cast iron radiators. The home has 1 main zone that heats 90% of the house and a 2nd zone that heats only the kitchen and mudroom via 2 beacon morris kick space units and 1 cast iron baseray unit. Both zones utilize Taco 007 F5 circulator pumps located on the return side of the boiler. No outdoor reset. Zone 1 (main) distribution piping consists of large 4" cast iron mains - I assume that the system was converted from steam at some point in the past - and 1" branch piping to the radiator units. Zone 2 (kitchen) is piped with 3/4" and 1/2" copper distribution piping. We moved in approximately 1.5 yrs ago and installed a stainless boiler flue lining a few months ago.

The kitchen zone seems to operate fine and is controlled by a mechanical thermostat. The aquastat is set for 180 deg and it reaches temperature and water seems to circulate well.

The main zone will only reach 140 degrees before the programmable thermostat is satisfied and the call for heat ends. The total cycles can be quite long ranging from 20-30 mins. My concern is that while the main zone is firing for 20+ mins the aquastat temps range from 100-140 degrees and the flue gases may be condensing. Anyone here have any ideas of what's going on?

Jamie Hall

Two thoughts. First, almost certainly not steam, but gravity hot water originally. Bu that's minor.

What we do need is the temperature of the water leaving the boiler, as well as returning.

kfCT1

Thanks for your thoughts, Jamie.

Would a simple IR thermometer reading of the supply/return piping give a good enough approximate reading?

Zman

The IR would work if you put something nonreflective on the pipe. Black paint or tape will do the job. With sustained operation at 140, you are almost certainly condensing in the vent and perhaps the boiler. It would be a good idea to have both looked at.
At 35 years old, you might start looking at new boilers. A new condensing boiler would perform well with your old gravity system.

EBEBRATT-Ed

@kfCT1

Your system is a converted gravity hot water system. There is some cause for concern due to possible boiler damage from cold return water and condensing.

Best way to fix this is to move the pumps tot he supply pipes and install a bypass pipe with a 3 way valve and a temperature sensor on the boiler return.

But

Your boiler is almost 40 years old. What condition is it in?

If it's lasted this long I would budget for a new boiler and make sure the replacement is piped right when it is installed.

That's easy with the right installer....they are difficult to find

kfCT1

Thanks everyone. I have a service company that has looked but I'm not sure how thorough they are. Difficult to get readings on the supply and return temps. When the boiler cycles, it tends to run from cold (approx 100 degrees) until the thermostat is satisfied. Long cycle of approx 20-30 mins. At the shutoff point the supply is around 140 degrees, return is probably 110. I suspect the circulator is probably undersized for the volume of water in the system (Taco 007 F5) and not ideal being on the return end.

I have started to look into new boiler options. I just bought the house in 2020 and many parts of the house have been neglected. For 40 years old it seems to be in ok condition in terms of corrosion on the heat exchanger. If I can get another season or two out of it, that would be great. I planned to replace when we moved in but with the supply chain and demand issues lately I would prefer to wait if possible.

If anyone has recommendations for a good installer in central CT I'm certainly open to suggestions! I have met with a couple and haven't been impressed with their expertise.

flat_twin

Sounds like your main zone is over radiated and able to satisfy the thermostat long before getting to 180. While you're searching for a qualified installer you could do your own heat loss calculation with the Slant Fin app. You could also research your radiators to determine their EDR at various supply water temperatures. It does sound like your heating system would be a good match for a modcon. Our one zone system with 10 radiators runs in the condensing range all winter down to minus 20. Seven years in and we're very pleased with our modcon for heating and domestic hot water with an indirect.

kfCT1

@flat_twin That's a good point. We have about 27 cast iron radiators on the main zone. Piping seems to be set up such that it will be easy to separate into at least 2-3 zones.

EBEBRATT-Ed

@kfCT1

PM @Charlie from wmass

he is busy so you may have to wait. I don't know of anyone else in central CT. What town are you in?

If it's been running that way since 83 it will probably last another few years

kfCT1

@EBEBRATT_4 Thanks for the rec. I'm in West Hartford. I messaged Charlie seems like he would be a good fit and knowledgeable with the old gravity converted systems. I'd rather plan ahead and install the right system than get stuck in a pinch and toss in whatever is available.

Separate HWH is at 10 yrs so it could be a good time to go to a condensing boiler w/ indirect water heater. I saw one of Charlie's posts from a few years ago and it sounds like he's done a number of the Lochinvar Knight setups. Those with skills and knowledge seems to have plenty of work!

flat_twin

kfCT1 said:

@flat_twin That's a good point. We have about 27 cast iron radiators on the main zone. Piping seems to be set up such that it will be easy to separate into at least 2-3 zones.

27 radiators, wow!

Before thinking any further about having more zones, how is the comfort from room to room? If the answer is good with very little temperature variation I'd leave it alone. Being over radiated is exactly what you want with a modcon. It allows for much cooler supply temps as you're finding out. Having most of the house on one zone (especially with large pipes and cast iron rads) makes short cycling much less likely. The problem may be getting the kitchen/mudroom zone to respond to lower supply water temps like the rest of the house.

mattmia2

Alternately, you might need to look at a modcon that can have multiple heat calls at different reset curves so you can supply hotter water when the kitchen zone calls.

kfCT1

@flat_twin Another good point. The thermostat for the main zone is located centrally on the 1st floor and the comfort is very good all things considered with minimal temperature variation room to room. I spoke with Charles Garrity and he was very helpful and is looking at the system for some improvements and solutions to mitigate the condensing concerns.

@mattmia2 That sounds like a great solution but I'm not sure about investing in a high efficiency unit given the insulation of my home. Solid masonry exterior walls with a 1" air gap then plaster over celotex board so no insulation in the house except for R15 batts in the remodeled kitchen. Original double hung windows with triple track storms. Planning to improve the attic insulation - currently a walk up attic (unvented with 3 operable windows) with loose fill cellulose in the 2x8 joist bays.

EricPeterson

@kfCT1
You may benefit from my experience.
Our house was built in 1917, face brick construction with no insulation in walls or ceilings. It has a converted gravity system piped and sized for the original 10 freestanding radiators. A family room addition (before us) added some copper-finned radiators.
When we moved in the first project was to replace the copper-finned radiators with 9" WM CI baseboard and put them on a separate zone. After that the basement mains were re-piped to split the original house into two zones (1st floor, 2nd/3rd floor) and also the near boiler piping was redone. Other projects added some insulation to different parts of the house, mainly upstairs, and an addition saw the adding of 7" CI Burnham BaseRay for two of the rooms, and another radiator for a new bathroom. To balance the heat TRVs were added for rooms on the second floor and the thermostat placed in the coldest room. Note that a side benefit of TRVs is that you can safely shut off the heat for individual rooms without fear of pipes freezing. The end result has been a very comfortable house.
After all the work the boiler (dated from 1954) was finally replaced with a CI atmospheric-vented model. I considered many options before deciding. I did a heat loss calculation and also figured out the EDR of my system as well. Since I determined that for much of the heating system the needed water temperature exceeded the threshold where condensing boilers remain efficient (see below), I opted for the simpler boiler design.
Protection for return water temperature was made by incorporating a system bypass. I would like to improve on this and use a ESBE VTC 3-Way Thermic Valve or equivalent.

Hope this helps,
Eric Peterson

kfCT1

@EricPeterson Thanks for sharing! Sounds like the system bypass might be the best solution at this point with the hope that I can get a few more years out of my current boiler then replace in kind and retain the piping configuration. I like the idea of the MCB, but for my application I don't think it's worth the cost.

EricPeterson

@kfCT1
Your boiler is almost 40 years old so if it's still working perhaps no immediate changes are necessary.
What you probably need more is a plan for the future. Good luck with that.
But in the interim you should find someone to service it, which should help you with finding someone you would trust to make changes later on.

My boiler was 56 years old when it was replaced. By that time roughly 25% of the burner mantles had been removed due to corrosion, I suspect from years of flue gas condensation.
It operated all those years without any kind of bypass. Nor was it ever serviced on a regular basis as far as I could tell. I recall that the combustion chambers were packed with soot so much so that one day there were flames coming out the sides at the bottom of the boiler.
Although it had been "modernized" from the original gravity boiler, parts of the original system were still in place, including a disconnected expansion tank located in the attic, and 4" mains. I wish now I had taken pictures of all that old stuff. Maybe my wide did, I'll have to check the photo boxes.

27 radiators in your place - wow that is a BIG residential system.