retrofitting 1952 single loop boiler

here_to_learn · April 2023

I currently have what seems to be original 1952 Janitrol boiler (60% efficiency and needs some work to fix). We have been heating with gas forced air furnace, but I miss the radiant boiler heat and desire to replace it. Also, I want to plan for replacing our hot water tank. My thought was to get a high efficiency modulating boiler and indirect hot water tank. I have a contractor (who has worked in HVAC about 20 years) who has installed and worked on some boilers, but it is not what he works on regularly. I’d like to learn what is involved with changing my original system over to this new setup.

Load calculation:
I have used loadcalc.net (Whole House Block Load) to find 47k btu/hr total btu’s heating when leaving Construction empty. When selecting Construction “good”, the heat load is 53k btu/hr.
A blower door test showed 4500 cfm50 and about 8 ACH50 of leakage. I’d love to keep improving this, yet I have done significant amounts of improvement on my own (when I first purchased the home, an energy auditor was not able to calculate the leakage due to huge leaks everywhere!).

I’ve also used Dana Dorsett’s load calc (involving monthly past usage and HDD65/HDD60) to calculate a heating load around 43k btu/hr.

Current boiler setup:
To my understanding, the current boiler system has a 2” O.D. piped single loop for first and second floor that is all run with one pump. There are cast iron radiators (10” x 2” x lots of 2’ connected pieces for each section) in every room. There are what I’ll call dampers on each section to adjust the flow and what I’ll call two smaller line branches off the main 2” O.D. line (one going to each end of the CI rads). We have not used the boiler in a while, but when using we would occasionally bleed air out of a vent upstairs by loosening the rad vent.

Goals:
I want to replace the atmospheric combustion boiler and hot water tank with say some type of sealed combustion like high efficiency boiler with indirect tank. It would also be nice to setup a future zone for the garage. I’m drawn to the mod-con boilers, since the idea of dialing in an outdoor reset curve to optimize intrigues me. I like optimizing, and I like deals.

I’m thinking that 60k btu input is the desired size, and I understand the importance of a larger turndown ratio (for design day vs. normal run time operation).
I am uncertain about advantages in this setup for firetube vs. water tube boiler.
I’ve read through the manual of Rinnai I-series boiler. Yet, I am open to any brand and realize the install is very important.

Any ideas and thoughts the community could share about products needed for such a retrofit/install and how to approach this retrofit would be highly appreciated. Thanks!

hot_rod · April 2023

Maybe do a radiator assessment. Size and output.

With the current and ongoing building upgrades you may be able to run lower SWT to meet thise loads
That would further leverage a condensing style boiler.

Many good mod cons to chose from, find out what is most common in your area for service and parts availability

EdTheHeaterMan · April 2023

This appears to have a 1-1/2" x 3/4" (or 1/2" to smaller radiators) diverter tee system by the looks of that last tee before the elbow down the the circulator pump. I would caution against moving or adding new radiators to that system. If there are any renovations or additions to the system that require additional radiators, I woulds connect any new heat emitters (radiators) to a separate zone on a separate circulator. The Dead Man that did all the math on sizing those radiators and diverter tees that have worked well for the past 60+ years will not like it if you mess with his work, and may just come back from the Dead to make sure you are uncomfortable.

Pictures of the radiators or heat emitters will help to determine if a small adjustment to the radiator location or adding or removing just one of them will cause any problems. But that said, if you add a Modulating, Condensing boiler (ModCon) to that system and scrap the old Janitrol "Ships Anchor", you will realize a much lower operating cost.

Best of Luck with the project.

Mr. Ed

here_to_learn · April 2023

hot_rod said:
Maybe do a radiator assessment. Size and output.

With the current and ongoing building upgrades you may be able to run lower SWT to meet thise loads
That would further leverage a condensing style boiler.

Many good mod cons to chose from, find out what is most common in your area for service and parts availability

Thanks hot_rod. I'll look into this ASAP. From my research, I'm thinking the baseboard rads EDR is 3.4 sqft per linear foot. Then, to determine BTU/h, would I use some de-rating factor depending on the water temp?

There are some rads stored in the basement that were removed during a kitchen remodel, so I understand that some additional heat might be needed there. Yet, there was some major air sealing done in that room. Each rafter bay was open and created a chimney effect. (This is building climate zone 5.) The crawl space below half the kitchen was open dirt, and it is now air sealed and insulated from the 3 outside walls and floor. In rooms with large windows, there are long lengths of rads, likely due to the original single pane and leaking windows. In the basement, the original single pane windows, which I'll change sometime, have a fin tube heat source in the main line near each basement window. So, I imagine lots has changed.

here_to_learn · April 2023

hot_rod said:
Maybe do a radiator assessment. Size and output.

I found 172 linear feet of cast iron baseboard radiators. Also, there is about 11 feet of what I'll call fin tube (fin tubing connected to the main line). I'm wondering how to calculate the btu/hr at certain water temperatures.

There is an additional 11 linear feet of cast iron baseboard radiators in storage/not connected.

here_to_learn · April 2023

EdTheHeaterMan said:
This appears to have a 1-1/2" x 3/4" (or 1/2" to smaller radiators) diverter tee system.

Mr. Ed, it took me a moment to notice what you were seeing here. Yes, I confirmed that is the size.
Here is a pic of a CI baseboard radiator and a diverter tee. Would any other pics be helpful?

EdTheHeaterMan · April 2023

I have made note of your 172 lineal feet of cast iron baseboard. I am concerned about the 11 feet of fin tube baseboard. the pressure drop across 11 feet of 3/4" copper and the pressure drop across the larger internal chamber of cast iron baseboard might lend itself to an imbalance of the heating output of the two different design heat emitters. One might argue that the less restrictive cast iron may allow for more flow and therefor more heat transfer in the room with cast iron compared to the room with the fin tube. Unless careful consideration of that pressure drop or just dumb luck came into play, I would not be surprised if there was a difference in the way the two rooms heated on each cycle.

Another thing to consider is the removal of some heat emitters in the remodeled kitchen. Since there is a restriction built into the design of the Diverter Tee, and the branch is actually the relief for that restriction, if the removed radiators were capped off at the Diverter Tee, that relief path thru the radiator is no linger there, but the restriction is still there. That can't be good for the design. Look at page 21 and 22 of this book to get idea of how the Diverter Tee design works. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf

mattmia2 · April 2023

Even the best glazing has a much lower r value than average wall assemblies so if you have tens of square feet of glass in some rooms you will need significantly more heat in those spaces.

mattmia2 · April 2023

If the person doing it doesn't do hydronics much make sure they do their homework, they will have to be careful to use the right circulator to get enough flow in the monoflow loop to induce flow in the emitters through the diverter tees, This also means it will need to be piped primary secondary. Caleffi has some great hydraulic separators that make the primary secondary neat and have ports to mount some of the boiler trim.

here_to_learn · April 2023

@EdTheHeaterMan
Regarding your concern about the 11 feet of fin tube baseboard, I'd like to ensure we are talking about the same thing. I have attached pictures of one of these. Is this called fin tube baseboard? There are two sections of these (about 5'6" each). Each was put in a basement room near windows and part of the 1-1/2" main loop.

EdTheHeaterMan said:
Another thing to consider is the removal of some heat emitters in the remodeled kitchen. Since there is a restriction built into the design of the Diverter Tee, and the branch is actually the relief for that restriction, if the removed radiators were capped off at the Diverter Tee, that relief path thru the radiator is no linger there, but the restriction is still there. That can't be good for the design.

They were capped, as you guessed. Your explanation and diagrams make sense. (I wonder if this is related to the rads in the kitchen feeling much cooler. I don't know about inconsistencies in temp in that room. Yet, I always assumed the rads were cooler, since they are at the end of the heating loop and there is less lineal feet after the kitchen remodel. Maybe the decreased flow contributed more so.) Thanks for the info. I suppose that it would be best to remove those Diverter Tees.

here_to_learn · April 2023

mattmia2 said:
Even the best glazing has a much lower r value than average wall assemblies so if you have tens of square feet of glass in some rooms you will need significantly more heat in those spaces.

I agree and can confirm there are a lot more in each room with windows. Surprisingly, the two westward bedrooms have the most lineal feet (yet not the most windows or size). I assume this was due to how leaky those rooms were, yet significant improvements were made in air sealing below these rooms.

All windows (except in the kitchen remodel) have rads the full length of windows or more. If adding some additional heat under the floor in the kitchen, what considerations would need to be made? I'm imagining the restriction in those tees that Mr. Ed pointed out could be used. (Maybe I could put something in the newly conditioned crawl space or under the subfloor in this kitchen space. I could even put the removed CI baseboard rad in the newly conditioned crawl space below the kitchen, yet I imagine there are much better alternatives).

mattmia2 said:
If the person doing it doesn't do hydronics much make sure they do their homework, they will have to be careful to use the right circulator to get enough flow in the monoflow loop to induce flow in the emitters through the diverter tees, This also means it will need to be piped primary secondary. Caleffi has some great hydraulic separators that make the primary secondary neat and have ports to mount some of the boiler trim.

Thanks again. I'm trying to do my homework, and I will need to ensure that the person doing this does so too.

mattmia2 · April 2023

here_to_learn said:

All windows (except in the kitchen remodel) have rads the full length of windows or more. If adding some additional heat under the floor in the kitchen, what considerations would need to be made? I'm imagining the restriction in those tees that Mr. Ed pointed out could be used. (Maybe I could put something in the newly conditioned crawl space or under the subfloor in this kitchen space. I could even put the removed CI baseboard rad in the newly conditioned crawl space below the kitchen, yet I imagine there are much better alternatives).

If you want to add radiant under floor heating to the kitchen that will have to be a separate loop off of the boiler. It will need to be supplied with a lower water temp than the CI baseboard and the fin tube. The radiant loop will also have too much flow resistance for the monoflow diverter tees to supply.

here_to_learn · May 2023

For those that may be researching a similar situation, I found an excellent article
https://idronics.caleffi.com/magazine/25-lowering-water-temperature-existing-hydronic-systems
It contains lots and lots of info. It has ways to calculate water temperature after lowering the heat load.
This depends on factors like original (in my case 1950s) design water temp and BTUH. I assumed original water temp to be 180 F since CI baseboard rads. I approximated original design heat load to be a little over 120,000 BTUH. Assuming this, I seem to be calculating that the new water temp at design could be in 130s. (Yet, I do need to recheck my work.

)

Thanks everyone for the very useful info and ideas!

retrofitting 1952 single loop boiler

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