Old cast iron system upgrade design review/help

JakeCK · August 2019

New to the forums, but I've been lurking for a while since I bought my old house almost a decade ago. This forum has been instrumental in helping me understand my 90+ year old hydronic heating. So thank you. Now to the fun part, bringing this old system to the 21st century... For starters I've called probably 15 or more HVAC companies around here that claimed to be knowledgeable in hydronics and have been met with liers, cheats, people to busy to even return my calls, or people giving me astronomical bs estimates over the phone. Oh and those who do come out shy away from the project. So I'm left to attempt this on my own.

The facts:
~30yr old Weil McClain CGM-5 series 9 140k input 115k btu output. Old and WAY oversized but shes in good shape and still kicking strong so she stays put for now(hopefully until after I insulate the house)

For heatloss I once spent a night recording run times on a very cold Janurary night a few years back. At ~3F the boiler ran for about 35min/hr. When I worked out the math it came out to around 67k BTU/hr. I've also noticed when we get below 0 the aquastat shuts off the burners(for some reason its set to 150f). After I used a worksheet to calculate the outputs of all the radiators it made perfect sense. They were sized correctly for the design temp even 90 yrs ago. Cleveland design temp is 5F if I'm not mistaken.

All CI radiators on 2 two pipe loops(one loop front and one for the back of the house) And just recently had an abatement company remove all the old asbestos pipe insulation. so I'm clear there as long as I don't cut into the walls.

Radiator sizes @ 140f:
Living rad1: 4500btu
Living rad2: 5300btu
Dinning: 8600btu
Kitchen: 7800btu
Bath down: 2700btu
Vestibule: 3600btu
Master bed: 8900btu
Front bed: 6400btu
Back bed: 7700btu
Bath up: 5700btu

Downstairs: ~32.5k btu
Upstairs: ~28.7k btu
Total: ~61k btu

The plan: I'm wanting to setup primary/secondary loops with a 4 way mixing valve to give me ODR and boiler protection. The secondary would have 7 zones with only 5 actually setup, the other two for future expansion into the walk up attic, and full basement. The Primary would have a second set of closely spaced T's that are capped off for potential indirect DHW. Current gas hot water tank is already 12yrs old. I would be using zone valves and a zone controller plus a infinite variable ECM system circulator. The boiler circulator that it currently uses would remain. I would however move the expansion tank so the pump is pulling from it and a new air scoop. Other features I want to add are lots of isolation valves. One for each radiator and other service points in the system. Differential by-pass(not really needed because of my choice in circulator but for 30$ w/e), drain valve, flow check, and wye strainer.

Each bedroom would be its own zone with thermostat, and the main floor would be on its own. Because of the number and size of radiators on the main floor I would run a 1" supply to a seperate manifold. 4 1/2" and 1 1" zone valves and 28 isolation valves. Did I mention I wanted a lot of isolation valves? I do not want to be caught in the middle of january with no heat a whole day because I have to drain the entire system because of something stupid EVER again.

Here are a few pictures and a couple plumbing schematics. Please don't mind my horrible hand drawing and writing.

Edit: Forgot to add the reason I'm doing this is both to free up space in the basement, I've hit my head one to many times and would like a man cave. Also when I set it to a comfortable 72 downstairs I sweat balls in the master, or of my room is comfortable there are cold feet downstairs and the other bedrooms get chilly.
I would also be using 1/2" pex-al-pex to each rad. And on my diagram I forgot to draw the isoltion valves around the boiler.
My biggest concern is how small the bedroom zones are relative to the boiler. When I replace and downsize the boiler and/or add DHW it would be less of a concern. Until then I might tie multiple zone valves together just so keep the boiler from short cycling.

Ironman · August 2019

If it were my house, I’d leave it alone until the boiler is replaced. Your plan for p/s, a 4way valve, etc., may not be necessary with a fire tube mod/con.
You also need to abandon the idea of a thermostat in every room. That would short cycle the boiler to death. TRVs are the answer there. And you don’t use a pressure bypass with a delta P circ. It’s either or, but not both.

psb75 · August 2019

Put in a Viessmann boiler and a Viessmann low-loss header. Skip the 4 way valve. Put TRVs on radiators. Magnetic dirt separator is a must. Get rid of the thermostats--run the boiler on ODR.

hot_rod · August 2019

If you do upgrade and use a boiler style the recommends a low loss header, take a look at the Sep u.

The only true 4 in 1 device for air, dirt, magnetic & hydraulic separation. Plus an insulation shell.

JakeCK · August 2019

> @Ironman said:
> If it were my house, I’d leave it alone until the boiler is replaced. Your plan for p/s, a 4way valve, etc., may not be necessary with a fire tube mod/con.
> You also need to abandon the idea of a thermostat in every room. That would short cycle the boiler to death. TRVs are the answer there. And you don’t use a pressure bypass with a delta P circ. It’s either or, but not both.
>

Dropping the bypass from the design is easy enough. My plan was to just have it there but set high enough it would never open with that pump.

I've kind of shy'd away from mod-cons due to cost/maintenance/reliability. The yearly maintenance just to keep the warranty would cost more then the savings at current gas prices. Don't all mod-cons call for p/s loops as well in the install manual?

Another reason I'm looking at thermostats in the bedrooms is for smart home control and not TRV's is so I don't have to play with 90 year old CI radiators. The other solution is a centrally located thermostat upstairs and controller controlling the valves for the bedrooms?

JakeCK · August 2019

> @psb75 said:
> Put in a Viessmann boiler and a Viessmann low-loss header. Skip the 4 way valve. Put TRVs on radiators. Magnetic dirt separator is a must. Get rid of the thermostats--run the boiler on ODR.

The smallest viessmann is 125k btu, that is bigger then what I have now. For a mod-con that is a huge waste?

A magnetic dirt separator looks simple enough to install.

JakeCK · August 2019

> @hot_rod said:
> If you do upgrade and use a boiler style the recommends a low loss header, take a look at the Sep u.
>
> The only true 4 in 1 device for air, dirt, magnetic & hydraulic separation. Plus an insulation shell.

What does something like that cost? It would certainly reduce complexity of the system. That is always a plus for service and reliability.

Edit: I actually like that but wow is it pricey. $670 compared to about 200 installing all of that capability with individual components.

JakeCK · August 2019

Could the controls be setup where when a zone calls for heat it only opens the valves and turns on the pumps? And if only the water temperature in the boiler is sufficiently low enough turn on the burners? Then have a minimum runtime to prevent prevent a short cycle?

A new boiler in addition to replumbing the whole thing is not in the budget as much as I would love to get something more appropriate for the size of the house. Remember the primary reason is to free up space in the basement, not to save on monthly gas bills. More comfort and better balance is just a secondary goal. If I had to I would forgo the zone valves and but still use a manifold and home runs to each rad.

Edit: A buffer tank would also eliminate the short cycling problem, but cost almost as much as a new boiler.

Old cast iron system upgrade design review/help

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