From Wall Hung to Cast Iron -- radiant / baseboard / indirect hot water

JPennHill · January 4

Hi folks - I am not a plumber in real life but I play one in my head…. actually, just a homeowner doing a bunch of due dilligence as I work with local plumbers to plan a boiler replacement for my bunker in Northern New England.

Long post - hope this is okay.

In short, can I use a cast iron propane fired boiler (130K btu range) to heat 2 radiant zones, some basement baseboard, and an indirect domestic hot water (DHW) tank?

More detail.

My timber frame house is incredibly well insulated and air tight - on a very windy / cold hilltop.

Currently have a 10 year old wall hung propane fired Buderus (130K btus) supplied 2 radiant zones (1500 sqft per zone), about 20 ft of baseboard for 1500sqft basement, and a 60 gallon HTP indirect domestic hot water tank.

Buderus is out of business and a recent failure took 4 weeks to resolve due to parts.

I use a woodstove to heat upstairs and have a wood stove (in basement) as well that I use for these types of situations.

Obviously, not a sustainable situation for Northern New England.

Current air supply and venting is via 3" PVC. Air supply is horizontal 30' (corrected for bends) and 67' for exhaust (up through roof and corrected for bends).

One vendor has recommended an IBC wall hung replacement - vendor says that their IBC unit supports interfacing into PVC exhaust. IBC literature seems to confirm this. This seems like the simplest plug and play solution.

Another vendor is recommending a Viessmann wall hung but Viessmann doesn't support venting into PVC (I asked them). This vendor said it would be fine. This to me is a red flag.

Another vendor, old school guy (like me), is recommending either a Viessmann in a different location to allow for quick venting through an outside wall then piping supply and returns 40' over to distribution (current) location.

This old school guy is much more keen on cast iron boilers. From what I can tell - a lot more sense - simpler, longer life; only downside is less efficient and more external controls to interface with radiant / domestic hot water / baseboard. Really don't care about the delta in efficiencies — I think simpler is always better.

From what I can tell, all these wall hung units have 10-15 year life spans, and are more complicated and expensive to repair because of the electronics.

He is working up a quote to interface a cast iron boiler; exhaust will be into an Excel chimney (6" ID / 8" OD) that is currently servicing one of my woodstoves - obviously, the stove would no longer be allowed to play with that chimney.

Am assuming mixing valve to interface cast ironboiler into radiant zones.

Am I on the right track?

Thanks for any help. Really appreciated.

109A_5 · January 4

Hello JPennHill,

" Buderus is out of business " I thought it was part of the Bosch Group now.

Maybe set up both types for redundancy, especially if the Buderus still works.

pecmsg · January 4

How was 130K BTU/h chosen? High efficiency is fine as long as the water stays below 140°F, any higher and its no longer High Efficiency.

Buderus is out of business and a recent failure took 4 weeks to resolve due to parts.

Thats another issue with High Efficiency.

jesmed1 · January 4

@JPennHill said:

Really don't care about the delta in efficiencies — I think simpler is always better.

I'm just a homeowner/engineer, not a heating pro, but I'm also in the "simpler is better" camp, so I would definitely go with the cast iron boiler. Yes, it will be 10% less efficient, but your building envelope is well insulated and sealed, so you won't be burning a ton of fuel, meaning a 10% fuel savings isn't going to be worth the headaches that come with high efficiency.

So I personally would go with a cast iron boiler. If you have the money, you might want to look at an Energy Kinetics boiler. They are really nice, efficient as you can get from a non-condensing oil boiler, and long lasting. And their Ascent Combi can vent into polypropylene if your venting is an issue. Or you could do an EK1 with indirect. @Roger of Energy Kinetics frequently answers questions here, so their support is excellent.

If you don't have the money for an EK, I would get a Buderus G115WS cast iron (not wall hung as you have, so parts are not as problematic) or another cast iron Weil-McLain boiler to replace our existing WM cast iron boilers, which have been bulletproof and have survived 30+ years of low water temps that everyone says should have killed them.

Again, that is my non-pro homeowner/engineer personal preference.

hot_rod · January 4

but you get a lot more than just some fuel efficiency with a mod con. The modulation can be a big part when you multi zone. All the adjustments for reset, step firing, etc need to be considered. Combustion air issues go away with a mod con.

What makes you think parts for a cast boiler will be available in 10-15 years? The same electronics will be obsoleted. Gas valves, ignition modules, electronic relays.

Seems like a lot of failed electronic aquastat, on cast boilers if you check in on some of the other boiler service websites.

But if simple is the deciding factor go with a U.S. built cast or steel boiler.

Jamie Hall · January 4

Your fundamental question is — can you use a cast iron simple boiler with your combination of heating? And the answer is yes. No problem. In fact, what might be called the "interface" (how's that for a nice modern sounding word) between the heat source — the boiler — and your three loads will be much the same, regardless of whether the boiler is a solid old time cast iron one or the latest and greatest mod/con from someone. You will have primary/secondary piping, and three outputs: the indirect now and then, the baseboard, and the radiant. The fanciest of those is going to be the radiant, which really needs a thermostatically controlled mixing valve to mix the water temperature down to what the floor can manage. The other two — thermostats. On and off.

Parts and maintenance and installation is a big consideration — much bigger in northern New England than in the urban areas. For that reason I'd go with the simplest design possible. Which sounds like your old guy…

JPennHill · January 4

thanks to all for the info — another option is to sell my bunker and move down south:)

Kaos · January 4

First step, how much propane are you burning in a heating season right now?

JPennHill · January 4

https://forum.heatinghelp.com/discussion/comment/1831868#Comment_1831868

Boiler specs were determined by original plumber back in 2014 - as noted above, boiler is heating water to 180 +- for indirect DHW tank.

pecmsg · January 4

You need a Manual "J" load / loss calculation to determine the heat loss of the building. That 130 was probably a WAG at best.

JPennHill · January 4

https://forum.heatinghelp.com/discussion/comment/1831900#Comment_1831900

no clue :) - will have to go take a looksie.

EBEBRATT-Ed · January 4

One of the mod con "deficiencies" if you want to call it that is that they are great little boilers with high efficiency, modulation and quiet operation.

But 10-15-20 years and the parts are not available at any cost and when you can get parts they are $$$$. And the MFGS are constantly changing models and there is no standardization.

You also need a technician who can work on that boiler sometimes not easy to find.

Mod cons are more $$$ but you get more….but for less life expectancy

CI boiler you can always get parts to get it running, almost?? anyone competent can work on it. Parts are less$$$ and are available. Efficiency of course is a little less.

Your choice and not an easy one

pecmsg · January 4

https://forum.heatinghelp.com/discussion/comment/1831910#Comment_1831910

On a cold night (At or near your design low) See if that boiler cycles on and off and there corresponding times

JPennHill · January 6

Just wanted to thank everyone for their comments / help.

From Wall Hung to Cast Iron -- radiant / baseboard / indirect hot water

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