Cast Iron Boiler: A dinosaur ?

TAG

Just finished talking to the owner of a house I redid almost 20 years ago. Grand old stone victorian in Chestnut Hill, PA. Spent almost a year redoing it. The original 2 pipe hot water system was restored --- two new Buderus gas cast boilers with two indirects were installed. The system was expanded to include radiant floors in the kitchen and bathrooms -- also, much of the third floor that was previous for servant activity. It uses ODR for the most part and this was a confusion for the owner initially. We did not live in it long (3 years) ..... it ended up being too big and in the wrong location. The owner is a friend of a friend that we see occasionally.

He had a pump issue about 10 years ago and the service company installed the wrong pump .. that was fixed and I told him to keep another correct replacement on hand. He recently had one of the flue vent dampers go and the service company (different) told him he should think about replacing the system ! I told him a couple years ago that he should be thinking about replacing the indirects .. but, not the whole system.

The service company based this on the date of the install -- I label everything. I told him this was crazy -- they could run for another 20 years. I did again mention that he should replace the indirects and I would replace the second vent damper. I also mentioned some savings could be achieved switching out the main pumps to those that uses less energy.

The service company said they could cut his cost by 50% ... I said ...no way. Funny thing is one of the options was typical boiler that does not look like it does ODR ... they first recommended condensing units. You can just guess on the cost !

My real question: Buderus does not seem to have cast gas boilers anymore that will do ODR. The one replacement line specifically says can not use the ODR controls. I'm assuming the only way would be mixing valves?

motoguy128

One option could be to add a condensing boiler that would handle the indirect and would make water up to about 150F return water temp, then the cast iron would take over.

I find that high mass cast iron systems I run into only needs 120-140F water most of the year to satisfy heat loss and boilers will be condensing most of the time except the coldest days. Further, the water volume/mass is so high that you get passive ODR it a certain extent as the system will satisfy before you get up to medium or higher temps.

Couple ways to control and pipe this. The lower temp secondary loops like floor radiant should be pulled off the return end to maximize delta T. The condensing boiler should be upstream of the cast iron boilers on the secondary loop.

A really simple control might be to use a 2 stage thermostat, if you have a master thermostat, with adjustable cycle rate like a Honeywell T6, and have it bring on the cast iron boilers with W2. Set the condensing boiler with ODR from 100-160F (depending on model).

Also any domestic call is handled by the condensing boiler only.

Size the condensing boiler for maybe 50% of heat loss. Or for total EDR at 150F.

Just brainstorming some ideas.

You are correct, the cast iron boilers if water quality is good and minimal makeup should last 40 years. Vent dampers, gas valves, ignition controls and flame sensors, LWCO last only 20-30 years or so. Expansion tanks, pressure regulators and air vents last maybe 15-20.

Cast iron boilers are 80-85% efficient and a mod-con depending on water temp is 87-97% efficient depending on water temp and firing rate, but does have the advantage of using outside combustion air if piped as such.

TAG

I told him if the stars align and he was a good boy ... the heating Santa may get him 15 % going condensing -- 10% is more like it. There is no payback possible given the cost of the switch and the use of natural gas.

The old radiators use the boilers ODR -- plus there are the two room controls --- one for each water temp on the boiler that has the radiant.

The other boiler has panel and runtal radiators -- they all have thermo heads. No mixing valve on that boiler. Does have room controller.

It's a nice system and works flawlessly ...

ratio

It's true that dinosaurs aren't today what they were in the past, but think about how long they were Top Dog.

ethicalpaul

And it took a massive asteroid to take them out

Solid_Fuel_Man

If the system is truly a low temp system of say less than 140 supply, then mod/cons would be a decent savings. 

Would I replace a BUDERUS that was 20 years old and showed no sign of rotting out? Nope! 

I am only familiar with Buderus oil, so I assume it's a power burner for gas on a 3 pass boiler? Not a typical atmospheric burner type chimney heater?

Steamhead

Buderus is now owned by Bosch, and they still make atmospherics:

https://www.bosch-thermotechnology.us/us/en/ocs/residential/non-condensing-boilers-1098953-c/

and these models still appear in the R.E. Michel catalog.

Both the smaller model GC144 and the larger G234X use a Beckett AquaSmart control which has ODR capability.

TAG

The G is only available in a larger size -- starts at 160

The GC is available in the smaller size -- The last I checked you can't use it with logmatic controls -- ODR with lower return temp.

That was always the selling point ..... I