Debating adding a zone, replacing a cast iron boiler

WintersInMinne

Hello Heating Help,

I have been debating adding a second loop to our basement, and have been recommended doing that work (adding zoning and two panel radiators) alongside replacing the cast iron boiler that is from 2003. It’s an AO Smith 75kBTU input, 63.5k BTU output unit. New unit would be a NTI FTVN 85, heat only, 10:1 turn down. Would be keeping the 40 gal hot water cylinder as that was recently replaced (mid 2021). I have gotten a couple other quotes, this has been the best price and knowledge wise.

Our main comfort complaint is the oscillation of temperatures that come from the current boiler cycling on and off (runs about 8-10 hours on a cold day in the teens or lower, so 16 hours off, more like 4-5 hours on a 30 degree day). Also, the basement is mostly always cold as it is under equipped with emitters - we’d like to get it ready to serve as an extra bedroom for in-laws in case we need to have them stay over to help with a second child while the other bedrooms are all in use. Also just to have it be generally comfortable to use.

The somewhat high gas usage is another complaint

House is built in 1935, central MN, 1.5 story with a basement, fin tube baseboard on one zone. Basement is 800 sq ft, has 16 ft of fin tube that are improperly installed (pipes and fins hanging in the air, no back plate, odd DIY job from previous owners), main level is 800 sq ft, has 92 LF of fin tube, upstairs is 350 sq ft with 21 LF of baseboard. We also have a 3 head hyper heat Daikin heat pump set up that we use in the shoulder seasons (and honestly quite a bit throughout the winter) to add in heat to our bedrooms and the living room.

I guess the question is, what do people think of the plan to remedy the comfort issues of the house? I know there is more air sealing/insulation work to be done in the cold basement, but I feel like having it be on its own zone will be essential to making it comfortable year round, in addition to air sealing.

I have been encouraged by reading accounts of the the comfort benefits of a long cycling modulating boiler that can have the heat “always on” but raising it and lowering the output as needed. That is the main reason for wanting to change things and “upgrade”. I am not expecting huge savings, but 20% or so annually would be welcome, which seems possible based on what I have read. Should be enough to cover maintenance and a little bit more hopefully.

Annual gas usage is about 900 therms, with around 700 of that being the boiler, and the rest for DHW + other uses.

Thanks for reading!

Jamie Hall

You could all -- or at least most -- of the comfort advantages of a mod/con by simply redoing your present boiler a bit to add primary/secondary piping and circulation and outdoor reset to a mixing valve recirculating system for the emitters. Not a big deal. The boiler would still cycle -- that's the nature of a boiler which can't modulate -- but the controlled temperature constant circulation in the secondary loop would get rid of the temperature swings. The heat would be always on, just as you mention.

You could also add a nice second zone with its own better installed emitters for the basement, same principle.

If the old boiler has been well maintained and is still operating well, you might get 10% savings. I wouldn't count on anything much more than that from a new boiler.

hot_rod

It sounds like a common atmospheric boiler, so it may have some combustion air ducts bringing in outside air, do you see any around the boiler?  They can allow cold air into the basement whether the boiler is firing or not.

On the plus side for a new mod con, it modulates, it is sealed combustion, no combustion air needed in the space  It will be more efficient for some or most of the heating season if it can run condensing r temperatures.

I suspect the boiler you have is a copper tube, has it ever been serviced or checked?

EBEBRATT-Ed

If your going to do this do it right. Start from scratch if you want it to work.

1. do a heat loss or have one done. You can download the slant finn app and do it yourself
2. Check the baseboard sizes for each room and basement based on the heat loss you get. The baseboard will out put about 550 BTUs/foot of finned element
3. add up the baseboard BTUs on each zone and devide the # by 10,000 that will give you the gpm water flow you need for that zone. Once you know that you can size th e pipe. 1/2" pipe=15000 btu, 3/4=45000 btu, 1'=80000 btu


If you heat the basement it must be on a seperate zone to work

Your contractor SHOULD do all the above most will just guess because "we have been doing this for 40 years"


We here horror stories on here every day

So be careful.

If you need a contractor check "find a contractor" on this site or post your location. Someone my have a recommendation

WintersInMinne

hot_rod said:

It sounds like a common atmospheric boiler, so it may have some combustion air ducts bringing in outside air, do you see any around the boiler?  They can allow cold air into the basement whether the boiler is firing or not.

On the plus side for a new mod con, it modulates, it is sealed combustion, no combustion air needed in the space  It will be more efficient for some or most of the heating season if it can run condensing r temperatures.

I suspect the boiler you have is a copper tube, has it ever been serviced or checked?

Yes, there is a cold air intake hose that is in a “J” pattern in the basement. If we switched the boiler to a sealed combustion unit, but still have a hot water cylinder, would we still need the combustion air intake hose?

Our boiler has been checked up on, but not had a full “service” as none of the companies around here do cleaning of cast iron boilers. Not sure about the copper tube part - it is an AO Smith brand, “GB100 W-4 cond” is the model.

WintersInMinne

Jamie Hall said:

You could all -- or at least most -- of the comfort advantages of a mod/con by simply redoing your present boiler a bit to add primary/secondary piping and circulation and outdoor reset to a mixing valve recirculating system for the emitters. Not a big deal. The boiler would still cycle -- that's the nature of a boiler which can't modulate -- but the controlled temperature constant circulation in the secondary loop would get rid of the temperature swings. The heat would be always on, just as you mention.

You could also add a nice second zone with its own better installed emitters for the basement, same principle.

If the old boiler has been well maintained and is still operating well, you might get 10% savings. I wouldn't count on anything much more than that from a new boiler.

That is interesting to hear about add on options. I have not gotten a quote for something like that - some folks have told me that adding an outdoor reset to the existing boiler may not be possible depending on the model. This unit is an AO Smith GB100 W-4 cond, whatever that is good for.

I wonder what the cost comparison would be like for doing this work vs replacing it with a new boiler plus loop. Thanks for the suggestion!

Jamie Hall

The suggestion I made should be no more than a quarter of the cost of a new boiler... probably less. Problem would be finding a contractor who could figure out how to do it and do it. Where are you located?

WintersInMinne

Jamie Hall said:

The suggestion I made should be no more than a quarter of the cost of a new boiler... probably less. Problem would be finding a contractor who could figure out how to do it and do it. Where are you located?

St Paul, MN

hot_rod

Eric Aune, Aune mechanical is in that area, he could recommend someone if he doesn't service that area.

Midwest Sales is a top hydronics rep in that area, they could give you a list of contractors. www.mwsmrep.com

WintersInMinne

hot_rod said:

Eric Aune, Aune mechanical is in that area, he could recommend someone if he doesn't service that area.

Thanks, will reach out and see what response I get.

WintersInMinne

hot_rod said:

Eric Aune, Aune mechanical is in that area, he could recommend someone if he doesn't service that area.

Midwest Sales is a top hydronics rep in that area, they could give you a list of contractors. www.mwsmrep.com

So I contacted Eric, he said that he is a bit outside of the area to do work, and is not licensed in St Paul, and I have not gotten a quote back yet from another referred to place.

I am leaning towards going full boiler replacement, and adding 3 panel radiators on their own zone - one in the laundry room/boiler room (200 sq ft, 5000 BTU unit, maybe a bit oversized, but they will all have a TRV), two in the main room, each 8000 BTU's, to cover about 600 sq ft of space, that may end up partitioned in the future into two rooms if we make one space into a bedroom.

I am hoping that this downstairs loop will provide a base level of heat at efficient radiator temps, that will help the main level have more even heat by coming up slowly through the ceiling/floor interface. Then combine that with the modulating boiler, to have better year round comfort in the upstairs.

All in cost is fairly high, but doable I think with a 5 year loan. Hoping the comfort benefits are worth it, along with some savings from a more efficient system, as well as opening up more square footage of the house to year round use. Also hoping it would make the house more desirable down the road if we do decide to move in 5 years or so. The panel rads should make it look more modern down there.

Am I on a good path here?

WMno57

Install electric resistance heating in the basement, and save your money for your next home.

WintersInMinne

WMno57 said:

Install electric resistance heating in the basement, and save your money for your next home.

That's a route that I have considered, and may continue to. To install one baseboard heater would be like 4% of the cost of the larger boiler replacement + radiators. So it's tempting to just do that and see how it goes, while I keep air sealing, etc.