Copper fin steam radiators- can I make the heat last longer?

skimmer

I have a one pipe steam system. All black pipe up to the radiators (partially recessed in the wall) where the builder installed copper fin for the actual radiators.

Heats nice when on but it doesn't retain heat like my grandmas free standing radiators!

I was wondering if there was a way to retain the heat like my good old grandmas radiators used to.

Are there cast iron "plates" or something to that effect that I could lay on top of the copper fins that would retain the heat like the old free standing radiators like my grandmothers?

Don't get me wrong, when my boiler is running and the rads are giving off heat it's wonderful ,but they lose their heat quite quickly after the boiler shuts off. I would like to be able to keep the warmness that the old style radiators give off after the boiler shuts off

Fred

Have you tried setting the thermostat for maybe 3 cycles per hour to see if that evens out the temp swings?

Jamie Hall

The difference is in the mass of metal -- your grandma's radiators were, most likely, cast iron and pretty massive. They take awhile to heat up -- but they retain the heat for awhile, too. Your copper fin tube is much lighter and more conductive, and will heat almost instantly -- and cool just as fast. Just the way the physics of the thing works.

I'd try @Fred 's suggestion. It may work very well indeed in your situation -- but with one warning: be sure that your system is very well vented, particularly the mains! You want to set up your venting so that all the radiators begin to heat at as close to the same time as possible, and this may take some fiddling.

skimmer

No temp swings. Just wanted to retain the warmth of the radiator that's all.

Jamie Hall

skimmer said:

No temp swings. Just wanted to retain the warmth of the radiator that's all.

No can do. Copper fin tube, with an outdoor reset and constant circulation, can be made to have a constant -- or at least very slowly changing -- warmth on hot water heat. It could also be made to do that with a steam system capable of, and designed for, operating under a variable vacuum. Otherwise... no.

Brewbeer

Can the copper fin tube radiator be replaced with a cast iron radiator?

Fred

Brewbeer said:

Can the copper fin tube radiator be replaced with a cast iron radiator?

I would say that depends, a lot, on what size the run-outs are.
@skimmer , if you don't have temp swings, give up on the nostalgia and enjoy the warmth of your living spaces. You may be creating a problem that doesn't exsist.

jumper

When steam stops vent opens and that cools off whatever inertial heat there is.

Probably impractical in a house. But bigger buildings can have several boilers. So when too little steam is on line then there's always some heating. Never cuts out. Probably works better on two pipe. Crude but....

PMJ

This is the problem everyone has more or less. It would be more pronounced with all fin tube convectors. With the boiler on it's only speed (high), it puts out steam faster than is needed, rads fill more than needed for the conditions, then there is a too long off period before the next call for heat during which the rads cool down - especially ones vented to the atmosphere. Because the rads got overfilled, there is necessarily some amount of overshooting of the temperature each time. The longer the off period before the next call, the bigger was the overshoot. Obviously none of these things happened when the boiler was coal fired. The rads never filled, the fire never shut off, the rads never cooled down completely.

The way to improve your situation is to spread out the steam production either with modulation or controlled timed firings. That way you never put out a continuous amount of steam enough to fill anything. The next burn cycle then will come along before the rads cool all the way down because you determine when that is. You "pulse" steam into the system more slowly over time. Others here have stated that this timed cycling improved the same condition you describe significantly.

Beyond this, natural vacuum between burns also would help dramatically with the rads real hot then cold problem. Easy to accomplish in 2 pipe systems, it is being worked on in one pipe systems right now by several people on this forum.

The Steam Whisperer

Along the lines of PMJ, find out the EDR of the system and see if the boiler capacity can be reduced to just enough to meet the EDR. It seems, and makes sense, that lightweight convector systems do not need nearly as much boiler Pickup factor. I would try the EDR capacity plus 15%, assuming you use plenty of main vent capacity, very small capacity convector vents, and the steam mains are insulated in the basement. This will allow longer burner on times and shorter off times, tending to keep the convectors warm most of the time.

PMJ

Reducing total output capacity is what controlled cycling does. By managing total % on time vs off time you reduce the output of any size boiler to match the heat loss more closely. You reduce the total burn time per hour and extend the call time. My big boiler can never ever run more than 30 minutes total in an hour unless I am cold starting. 3-10 minute burns separated by 10 minute waits when it is really cold. But that big boiler sure is nice to have on cold starts.

Remember, the most even heat would be a call for heat that never ends. Temperature always in the deadband of the tstat.

jumper

No guarantee that the following will work. Plug all vents and evacuate air from system. Say 29" vacuum. Then some heat will still be given off for a while after boiler shuts down.

PMJ

Anyone wanting to try out vacuum should just start with the natural 1000/1 volume collapse of steam to water. That is plenty enough for a very big impact on things and zero extra cost.

The Steam Whisperer

I would suspect that would work really well with convector systems.....there is so little air volume that the system can be filled completely with steam very quickly and then a vacuum is formed. The volume collapse of steam to water is actually about 1700 to 1.... even more huge. Using natural vacuum with cast iron we often see about 8 to 10 inches mercury vacuum.

jumper

The Steam Whisperer said:

I would suspect that would work really well with convector systems.....there is so little air volume that the system can be filled completely with steam very quickly and then a vacuum is formed. The volume collapse of steam to water is actually about 1700 to 1.... even more huge. Using natural vacuum with cast iron we often see about 8 to 10 inches mercury vacuum.

Where would you vent? Would you put multiple valves on the vent?

Harry_6

I have a customer with a similar problem. An addition to his house was made in the 1920's, and instead of cast-iron radiators they installed something I saw in a period catalog listed as "copper tube" radiators (see photo). These also heat fine until the steam is off, then the temperature plummets. All the rest of the house is 2-pipe (vapor vacuum). Before replacing all five with cast iron rads (which would be hard to match, size-wise), I'm considering mounting a piece of black slate (with suitable gaps at the top and bottom for air flow) against the front of the coils to add thermal mass. I don't know how well this will work, but I figured it's worth a try. By the way, anybody seen these before?
-H

mikeg2015

Those units would I bet work ok with hot water with a mixing valve with outdoor reset.

Stone would be a good option. Be sure to leave room for air movement on top and bottom. Maybe 6”.

nicholas bonham-carter

Maybe switching the thermostat to 2 or 3 CPH would help, or going into sub atmospheric operation would even out the heat.—NBC

jumper

Water has highest specific heat. So if you can stuff sealed somethings containing water among those fins you'll get the most thermal inertia per pound.

mikeg2015

> @jumper said:
> Water has highest specific heat. So if you can stuff sealed somethings containing water among those fins you'll get the most thermal inertia per pound.

It’s funny. I was going to say the same thing. I sometimes wonder if a steam/water hybrid radiator would be nice in some downstairs areas where some extra mass is helpful. Could glycol fill it and leave some air in it for expansion.

You could almost have a CI radiator thats iron pipe across the base. You would need a prv on the radiator. But normally it would be under a slight pressure so it can’t boil.

jumper

mikeg2015 said:

> @jumper said:

> Water has highest specific heat. So if you can stuff sealed somethings containing water among those fins you'll get the most thermal inertia per pound.



It’s funny. I was going to say the same thing. I sometimes wonder if a steam/water hybrid radiator would be nice in some downstairs areas where some extra mass is helpful. Could glycol fill it and leave some air in it for expansion.



You could almost have a CI radiator thats iron pipe across the base. You would need a prv on the radiator. But normally it would be under a slight pressure so it can’t boil.

Good technical idea but how big a market?