Radiators versus convectors -- optimum use and placement

Narendra Varma

I am working on a home that used to have a two-pipe steam system that was converted to hot-water in the mid-eighties. The client would like to replace some of the old cast-iron radiators with panel type emitters (I'm hoping to use the replaced cast-iron radiators to heat the basement so they won't go to waste). A few questions about the various types of modern panels (radiant floor is not an option):

1) Fins or no fins: What is more "comfortable" in terms of its closeness to the ideal heating curve: panels without fins or panels with fins? It is my understanding that on panels with fins a larger proportion of the heat output is via convection rather than radiation. Is this true? Since radiant floor seems to be the closest to the ideal heating curve, I would imagine that the goal is to get more radiation and less convection from an emitter (although you would always have both).

2) Shape of emitter: Are there advantages or disadvanteges to using a long and narrow "baseboard" style panel rather than a more square panel? In some cases, the physical constraints of the room or aesthetic concerns make this a moot point but again, I'm wondering if one is theoretically better than the other.

3) Placement of emitter: In old houses, the radiators were usually placed under the window. Is this still considered the optimal placement if one is dealing with single pane windows and uninsulated exterior walls?

4) Brand: I have been looking at the Runtal and Myson catalogs -- Myson only makes on panel witout fins but it's limited to a 79" height. Runtal provides the option on all their models. Are their other brands available in the U.S. that one should look at? Any reason to chose one over the other?

Thanks for the help,

- Narendra

Steamhead

Mixing cast-iron and fin-tube will cause problems

if used on the same zone. This is because cast-iron holds its heat whereas fin-tube or steel panels cool down instantly when the circulator stops.

My first choice here would be cast-iron baseboard. It will behave the same as the old radiators. If you must use something else, give it its own zone.

Whatever you use, size it according to the same water temperature the radiators use now. This was usually 180 degrees on the coldest day of the year when these old houses were built, and may be as low as 150 now if the house has had insulation, storm windows or other such improvements added.

Optimum placement is still on outside walls under windows, since this is the coldest part of the room.

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Mike T., Swampeast MO

1) Panels with convective elements like "fins" will have somewhat greater output per unit of surface area. I would prefer those without convection enhancement unless such are required by physical space constraints.

2) At least one lab study seems to show that tall, narrow (about 2 to 1 aspect) panel radiators are extremely effective at delivering their heat via radiation.

3) Numerous studies are showing that placement of panels/radiators on inside walls is the "best". BUT, only in structures where infiltration is fairly low and insulation fairly high. With single-pane windows and uninsulated exterior walls traditional placement (best is under windows) is in order. If this is the case in your home AND you don't plan on changing this AND you plan on using panel radiators I would use short, wide, convective enhanced panels under the windows.

4) Buderus is another panel radiator company.

You didn't ask about this but if you use panel radiators INSIST on TRVs! The reasonable added cost will pay back not only in energy saved but in comfort. And yes, these devices are very reliable.

Ex Maine Doug

Flat Panel Rads

I am using Veha flat panel rads in place of the original steam rads in my building. One 43x38 work space with 14 foot ceilings and about 400 sq.ft. of windows on east, south and west sides. Last winter managed to get 3 connected with 3 more to do on the east side (seems other things made it to the to-do list). They are under windows and we were comfortable last winter with -6 degree temps. So I am not installing all 8 as originally planned. Downstairs we have radiant slab, concrete ceiling above the radiant slab.

So I am pleased with the flat panel Veha's. We drove the truck to Tamworth NH where Windy Ridge Corporation
had banded the rads to a pallet and loaded them for us.
Our fuel consumption is a bit less than half that of the steam system- we have installed insulated windows and foundation insulation but nothing in the ceiling space.
Email if you would like to see some pics.

Phil_6

Or...

...if you don't want to use the cast iron baseboard, install sunrad type recessed radiators. A little carpentry involved, but they take up less wall space and you don't have to assemble them

Phil

Steamhead

Comparing panels with steam radiators

really isn't valid unless both systems had similar boilers and were in good condition. Many times a steam system's fuel consumption is excessive because of improper venting, lack of insulation, improper pressure settings, inefficient boiler etc.

I find it's a lot easier and cost-effective to fix a steam system rather than tear it out and replace it.

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Ex Maine Doug

Good Point. Unfortunately the

steam boiler was located in what was to become the master bedroom. Also the big steam pipes hanging everywhere made for close encounters of the head banging kind. The steam system was functional although oversized. So it all had to go, plus all the plumbing, electrical.