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Cast Iron Baseboard, TRV'S. and Constant Circulation
Tombig_4 Member Posts: 45
I'am considering a new cast iron baseboard install with trv's and constant circulation. The system will be replacing an 80% natural gas furnace in a two story home with a single zone. Also, steel panel radiators are an option with the same set up. Any pro and con responses would be greatly appreciated.
You're on the right track
Either cast iron or steel radiators work great. You might size them for 160°F rather than the customary 180°F. I assume you will be using a modulating condensing boiler. An indirect water heater would be a good upgrade. When planning the mechanical, you might even leave room for a solar domestic hot water pre-heat tank in the future if you think that might be an option.0
If you have one zone, traditionally a system like that is a monoflow system. You could cut out the second floor and make it a two zone system.
A Viessmann Vitodens or a lochinvar knight would be a great choice in boilers especially if you are going to do constant circ with trvs. If it is in the budget definitely think about solar for future0
Cast iron is great but new american (cast) radiators (burnham) are very expensive. The steel panel rads. are much more affordable and many models incorporate the trv valve, all you need is the actuator.
Cast iron baseboard vs. steel panel radiator cost
Many thanks to everyone for their responses. Scott M., I agree with you. The cost of cast iron baseboard vs. steel panel is much higher, especially when sizing the emitters for mod/con low temps. I'am 99.9% sure steel panels are the right choice for my home.0
As for oversizing compared to 180° sized rads @ 100%, your sizing would be: (200% means buying twice the BTU rating)
150° @ 150% - assuming a ΔT of 15, that's a 135° max return
135° @ 200% - assuming a ΔT of 15, that's a 120° max return
125° @ 250% - assuming a ΔT of 15, that's a 110° max return
118° @ 300% - assuming a ΔT of 15, that's a 103° max return
113° @ 350% - assuming a ΔT of 15, that's a 98° max return
You could look at it like where is your best return at *or* if you ever plan on adding radiant floor anywhere, just use the typical water temperature for it. Higher for pex and plates like probably somewhere between 150 - 200% oversizing factor for the panels to run the same temps. If you would go something like Warmboard then go with their temps and oversize even more if you can. It'll make it much simpler to pipe and control in the future as well as give you more zoning freedom.0
Sizing Panel Rads
In my opinion, sizing panel rads for design temps below 140°F results in some very large or numerous radiators. I am more of a mind to size for 160°F with the assumption that the system will be running well below that 90% of the time and probably lower than that all of the time because of the safety factors built into the heat loss calcs. It may not be the ultimate in efficiency, but I think it's a decent compromise of radiator size and cost with efficiency. That's just my philospohy. There's nothing wrong with sizing for lower temperatures.0
This discussion has been closed.
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