baseboard vs. radiators

Brad White_172

on the ratio of radiator surface to heat loss. The one that is most generously sized to allow a lower water temperature is the one that will cost less to operate.

CI has a better radiant effect right to the body while fin-tube forms a film along the wall with good coverage (if applied correctly) so will reduce the walls mean radiant temperature (MRT) right off the bat.

If the CI is placed along outside walls will have a similar effect, the radiant portion compensating for spotty coverage (large radiator on one spot versus a baseboard).

If the CI is on an interior wall as in some original installations, you will have to run a warmer temperature for comfort and still may feel cold on the side of you that faces the outside wall...

All things being equal, BTU's are BTU's but give me cast iron :)

[Deleted User]

Is there any difference in monthly heating bills by using regular non cast iron baseboard vs. Cast Iron radiators for a hot water system?
Also will one work better then the other to heat the rooms?

Unknown

very well said ,Brad....

Very well said, Brad.... Cast iron base board, when installed properly, is considered the 2nd best heating comfort...

Eric Johnson

mixing the two

I know it's a bad thing to mix ci rads and finned copper baseboard on a zone, but I don't know why.

Is it OK to mix them in a house but on different zones, or better to stick with one or the other on one heating system?

Brad White_172

The reason it is not recommended

to mix CI and Fin-Tube on the same zone has to do with thermal mass in addition to emittance.

Baseboard has less mass and is convective. When water flow stops, the output drops rapidly and with it goes the convective effect, the barrier of warm air up the walls.

Conversely, cast iron will continue to emit radiant heat, diminishing more slowly until the radiator temperature and the room temperature coincide.

If your controlling thermostat is in a cast iron served room, the fin-tube rooms will cool off perceptibly while the primary zone continues to work. Reverse that and presume that a fin-tube room has the controlling thermostat. The CI-served rooms would tend to overheat.

When they are on their own zones or if you use continuous circulation with Thermostatic Radiator Valves (TRV's) you can achieve that elusively defined "acceptable comfort". (Issues regarding too many zones and short-cycling opens another thread.)

Many folks prefer one or the other entirely and if given a choice, cast iron by those who know

Mix CI and Fin-Tube without regard to basic principles will cause a major disruption to the earth's orbit; cats will mate with dogs and mice will rule the world. For those and other reasons, I say, "do not do that".

Steve Ebels_3

A tale of two emitters

Last fall we did an job which included Climate panel for a 750 sq ft new addition and panel rads for the existing 1800 sq ft of the house. Previous heat was poorly executed hot air.

I asked the owner how they liked the heat this past winter when I was at his shop a couple weeks ago. First he said they LOVED it. Then he delivered a very telling comment. "If we had known that the radiators made such comfortable heat we'd have probably skipped the infloor in the new addition."

The system is driven by a Vitodens 200 which of course provides variable water temperature and constant circulation. There is no "normal" thermostat in the house, just a TRV on each radiator. This makes a very simple system and provides such excellent comfort I don't know why anyone would consider anything else.

The owner also told me that the house used over 240 gallons less propane than the winter before despite the fact they were heating more sq ft.

Uni R_3

Hey Brad...

How much does constant circ help out with mixed emitters? Enough for it to work okay?

Brad White_172

Okay is the operative word

That is a bit subjective, Uni.

The temperature will be (or can be made to be) even but the perceived MEAN RADIANT temperature will likely vary.

The physical versus the physiological effect of "theoretical perfect temperature" compared against good radiant effect in one room and a convective barrier along the wall in another. Sort of comparing a "positive" with a "neutral"

The variables toward the extremes would be a room with a lot of glass and one with little, even if the radiation is sized precisely the same to the heat loss. You can imagine how each type of radiation, even properly applied, would have a different effect on a body.

But yes, short of replacing all the emitters with ones of one type, it is a cost-effective approach. Most people find the effect acceptable.

Mitch_5

Missing one thing

You can run Cast Iron at a much lower temp. Attach it to an Ultra on outdoor reset and you can run it like radiant heat. Especially in the old over sized homes.

Copper baseboard runs at higher temps.

Mitch S.

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Uni R_3

A BTU is a BTU...

A BTU is a BTU is a BTU and no matter which materials you chose to compare they will ALL transfer at any ΔT.

The difference will be in the efficiency of how different materials transfer heat over time.

Use better controls (listen to m-c boiler owners with fin-tube say how comfortable they are) and the whole industry could save on materials and most won't have to rely on cast iron for the comfort in any install. For some it's nostalgia.

ALH_4

Radiators

Time (rate) is extremely important. Radiators transfer heat at a higher rate than baseboard as fluid temperatures drop. For one, panel radiators provide a taller column of air to increase the stack effect and therefore increase the convective heat transfer. Secondly, the face of the radiator also radiates heat directly to the room, where baseboard relies solely on convection.

My favorite new emitters are steel panel radiators. I am not a fan of copper fin-tube baseboard simply because it is so easily damaged and generally looks pretty shabby after a while. If adequately-sized cast iron radiators are existing, there is little, if any, improvement to be made even with radiant floors.

I think the ideal system uses radiators combined with radiant in the kitchen and bathrooms.