Migration to Cast Iron Radiators

The nice thing about those radiators is that they will take all sorts of temps and still throw out a good amount of heat. I wouldnt think you would need to mix any of the temps down unless you have a strange zoning arrangement in the house that would cause a space to overheat with the 195 degree water.

Are you running multiple zones? Using thermostatic control valves on each radiator?

Donl said:

I just purchased a number of used cast iron radiators that I will use to migrate from forced air to all hydronic. I have completed a heat loss calculation for each room in our house and an estimate for btu output for each radiator. I use storage and my boiler system temperature ranges anywhere from 140f to 195f. My design temperature is 140f, so the rads should provide adequate heat on the coldest days while running off storage. My question is, should I supply a constant 140f to the rads using a mixing valve or just use what ever temperature is available from the boiler/storage (140 - 195).

What would be the best approach on this?

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Donl said:

I plan to use 3 or 4 zones. Each zone will have from 2 to 5 radiators connected in parallel back to a manifold using 1/2" pex driven by a grundfoss 15-58 circulators.

I have not planned on using thermostatic radiator valves (trv's). They are expensive and I have read they are prone to failure. I use a NFCS computer to monitor temps in each zone and control each circulatory when required. I hope to balance the radiators in each zone by a gate valve on each radiator.

I'm just not sure my plan will give me adequate control of output temperature with such a wide range between 140f and 195f. My goal is to provide an even comfort with all variables.

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Does the NFCS allow you to have somewhat of an "anticipator" setting? Since the radiators will continue to provide heat to the space for a bit after the circs are off, I wonder if the software could take the temp of your supply loop into account and shut down circs prior to meeting the setpoint in each zone, thereby avoiding ovheating the spaces. As your supply temps drop, the amount of anticipation in the controls would decrease.

No idea if thats something the NFCS can do...

Hey Don,

How many GPM will you be moving through your storage?

I think that some mixing control would maintain better stratification in storage, maybe?

Can you share a link to where you read about TRV's being prone to failure? In my research I found very favorable opinions of them both here and over at The Wall.
And as I have 7 installed in my house......

Thanks,
Noah

What stands out to me is you said you'd be using 1/2" pex back to the manifold. I guess the only radiators that come to my mind are those that use >= 1" pipe. Wouldn't 1/2" pex limit the flow too much ?

I have used cast iron rads for three years now and with a manifold in parallel 1/2" pex is fine. as for the controls, I have control valves on the manifolds but I just leave them all open. I find that the cast iron is real forgiving so I would not over think the controls. I would vote for keeping your system simple

NHFarmer said:

I have used cast iron rads for three years now and with a manifold in parallel 1/2" pex is fine. as for the controls, I have control valves on the manifolds but I just leave them all open. I find that the cast iron is real forgiving so I would not over think the controls. I would vote for keeping your system simple

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I second this! We tend to overthink controls sometimes. When it's in out own houses we can expierement, and sometimes TRVs and all are not needed, simple throttleing gate galve at each rad, as you said, and a centeral thermostat to control the circ. The 1/2" pipe and manifold setup is treating the CI rads like you would a panel rad, which is basically what they are just with alot more mass!

TS

An outdoor reset would be nice to have but is not a must. It will help to keep you from overshooting temps on more mild days.

Hi Don. I have all ci rads and I run them wide-open, so they're getting pretty hot water from time to time. I've found that the room stats (zones) do a good job of keep temps pretty even. I have to add that we err on the side of warm in our house. But I've also found, as Taylor suggested, that simpler is usually better with hydronic heating systems--as tempting as it is to lay on the controls.

I just have to say, I LOVE CI rads too. No need for them here though

I zoned my radiant with three zones, garage, living/kitchen, and the rest of the rooms. Got the fancy 5 loop manifold to accept the special zone valves (ebay) ran the thermostat wires, got the zone valve controller for it all...... Now the garage zone is all I use, the other 4 zone valves are not installed and run when the circulator is on. The garage is the second dump zone (after indirect). Controlled by two stage aquastat and a 24V transformer. Sold what I could recoup the money from.

Simple works better, we tend to overthink this stuff, it's not a commercial building with 100 rooms nundreds of feet from the boiler room, most of the doors are left open and interior petitions offer little insulation anyhow.

TS

Like you, Taylor, I've started out with a lot of fancy stuff, which eventually got removed or disabled or never used as situations developed that made it a lot more logical to just go the simple route. My advice, based on that experience, is to start simple and then add complexity once you use it for awhile, if desired. Saves time, money and head scratching.

Don,your are going to love those cast iron radiators.I made the switch 3 years ago and couldn't be more pleased.My original heat loss calculation also showed a need of 140* but in reality have never needed temps that high.I'm using a very simple injection mix system and last year the temps were leaving my storage at 110* and returning at 90*,by using these lower temps I was able to wring out all I could from storage.In my case I would burn a 10 - 12 hr fire every other day taking my storage to 200*,.by the way we keep our house at a constant 70*

Jeff S said:

Don,your are going to love those cast iron radiators.I made the switch 3 years ago and couldn't be more pleased.My original heat loss calculation also showed a need of 140* but in reality have never needed temps that high.I'm using a very simple injection mix system and last year the temps were leaving my storage at 110* and returning at 90*,by using these lower temps I was able to wring out all I could from storage.In my case I would burn a 10 - 12 hr fire every other day taking my storage to 200*,.by the way we keep our house at a constant 70*

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Here in Canada our hydronics code requires a max temp of 140 f for cast iron. I would definately use a thermostatic temp valve to lower the temp to the cast iron rads. The other thing to look into would be your delta t.. Temp sensors on both sides, hot and return lines. Temp differance of 20 degrees ideal. A storage tank is excellent. Is your boiler a chimney condensing unit, and or a boiler condensing unit. ( condensing in the boiler). Also. low temp hydronics seem to be better over all. (in floor). safer and less maintenance. Also, mono T's are an inexpensive way of helping direct water flow. Coupled with thermostatic control valves at the rads are a great way to manually control room( zone) heat.
Good luck.