Radiator replacements

[Magneto]

Hey so lately customers have been asking me if there is a modern day replacement for their cast iron radiators. I knew this day way would come considering all the money people are shelling out to renovate their households. Seems like cast iron is dying, along with baseboards and other types of convectors. I said I'd look into it and I have, Just wanted to know the general idea about this topic in the community. How are your local areas dealing with this new age in heating?

 

[Dana]

Steel low temp panel rads (Buderus, Biasi, Runtal, et al) are out there, with more contemporary look & feel than antique cast iron. The low profile flatter face cast iron rads like Burnham Radiant or OCS Cast Ray are still pretty available, if the customers don't object to the look. They don't scream "old school" quite to the same extent that column radiators do (even though variants thereof have been around since the 1920s), but they don't scream "ultra-modern" either, and were still pretty popular well into the 1950s in higher-end suburban housing.

Cast iron column rads and tube rads are still being made & used in Europe and parts of Asia, but are fairly uncommon in newer construction in the US.

Panel radiator variants:

There are thousands of variants of "heated towel rack" radiators for bathrooms out there in contemporary designs.

vs: Flat cast-iron still being made:

and definitely not older school some of which is being made for the restoration market:

 

[Sponsor]

 

[Magneto]

Thank you for the well spoken response, great presentation I really appreciate it. I have even seem to found a different type of modern radiator as well. They are also European style like you mentioned, they are made from aluminum and steel, called bi-metal radiators. Seem to have a pretty good btu output as well, and cheaper than cast iron from a quick look. Have you heard about these Dana?

 

[Dana]

Haven't heard of bi-metal radiators being sold in the US. They're essentially aluminum-clad thin die-cast steel radiators, with the ferrous metal on the water side, the aluminum on the outside, power coated or painted. The aluminum makes them less likely to develope corrosion / rust than all steel versions when the finish gets dinged up, I guess. (At least one manufacturer says so.)

A quick web search shows that they are usually radiating convectors, some similar to a SunRad in basic form/function, with the exit-air coming out the face of it rather than straight out the top (as most convecting steel flat panel radiators), while others convect straight out the top.

 

[Magneto]

Seems like your correct about the components. Aluminum body casing with a steel core makes for great thermal inertia for sure, but the big factor for me was the btu output highly exceeding what I thought it would be for an aluminum radiator. Seems these bi-metal radiators are two times more efficient than cast iron, and up to 3 times more efficient than baseboards according to my calculations. So apparently doing some more research there is actually an online store named Canarsee supply that sells them in a few different sections. Not the biggest variety but these seem to be just like the picture you posted.

 

[Dana]

The steel or iron is usually only a small fraction of the thermal mass in most old school radiators, since the specific heat of iron is only ~11% that of water by weight. A 100 lbs. steel radiator is comparable to 9.1lbs of water, which is just a bit more than a gallon.

These thin die-cast radiators don't seem to have much water volume OR iron weight compared to old school stuff. This one, has only 0.42 gallons/ 3.5lbs of water in it, and less than 22.5lbs of iron (= 2lbs of water-equivalent thermal mass.) The total thermal mass of it is equivalent to a couple quarts of water, but the water is more than half the total thermal mass even of this l0w-volume rad.

 

[Magneto]

So my next question to you is do you approve of these radiators, or would you still suggest a cast iron type for a modern household?

 

[Dana]

It's not up to me to approve anything. To my eye they look a lot nicer than fin-tube baseboard, and would surely FEEL better too, both of which are aesthetic considerations.

From a system design point of view it's easier to design with radiators that have some thermal mass in them, to mitigate boiler short-cycling. This is especially true in homes that have been micro-zoned, with zone loads even at the 99% outside design temp lower than ~7-8KBTU/hr which is about where the minimum modulated output of the very lowest-modulating boilers are. If the 99% design load is that small, the average load is even lower, and having some thermal mass in the radiation can avoid having to resort to buffer tanks or ridiculous amounts of radiation for the tiny zone loads to protect the boiler.

Steel panel radiators don't necessarily have a lot of thermal mass either. There's something to be said for old school type radiation, which has higher thermal mass in both water & iron form at equivalent BTU output. But new cast iron is comparatively expensive at some point the economics of buffer tanks as a solution look better, and not everyone is on board with the visual aesthetics.

 

[Magneto]

Well everyone's' opinions differentiate depending on their own personal style and taste. The economic standpoint is also a large factor of making a decision. My opinion is that the world is moving in a new direction, and with that direction come new territory. Old school radiation is soon to be forgotten about from my point of view. Then again maybe I'm wrong. I understand your point on thermal mass, and you have a solid understanding of the terms your using. Thanks you for your input once again.

 

[Dana]

Soon forgotten?

Old school radiation has already been forgotten. It is a nearly-dead business, selling primarily into older building restorations. I don't expect that to change. Most new hydronic systems in the US are fin-tube baseboard, which has even less thermal mass than panel radiators or bi-metal radiating convectors, and effectively zero radiated heat transfer. It's pretty inexpensive compared to aluminum radiators or steel flat panels, but it's not nearly as comfortable.

But hydronic heating are also losing market share to ducted hot air, in a US marketplace that increasingly demands air conditioning in new houses. I don't expect that trend to change either. High-end new housing often includes hydronic radiant floor/ceiling heating, but that's a niche market. A typical US HVAC solution would be a gas/propane fired hot air furnace with a cooling coil in the air handler and a 2-4 ton condenser outside. Even baseboard heating is losing share to that trend.

Micro-zoning is something of trend too, and responsive lower-mass low-temp radiation like convecting panel radiators or aluminum clad convecting radiators can work just fine at condensing boiler temperatures, as long as there is sufficient thermal mass in the system.

What I hope would change is the fraction of hydronic designers for new construction who do basic 5th grade math. A condensing boiler that can't operate at condensing temperatures in the system without short-cycling itself into low-efficiency (and an early grave) isn't worth much, yet it happens all the time.