Steam Cast Iron Radiators and Convectors to Hot Water

arborus14

I am working on the heating upgrade of an old building and have just finished the heating load calculations. The building has mostly steam cast iron radiators with some Modine type steam convectors. I have worked out the surface area of the radiators and convectors with Dan's book "Every Dam Radiator" and found the heating load can be offset with water temperatures as low as 160F. Even with a fairly hefty safety factor on the calculations. Were steam radiators back in the day (60 to 100years ago) oversized? I will likely keep the convectors (which are much newer than the cast iron) and replace the cast iron rads with a Jaga or equivalent. Looking for people's experience converting from steam to hot water.

hot_rod

How tall is the building? The radiators will need to to be pressurized at least 12 psi

Are they connected across the top? One ir two pipe connections?

Jamie Hall

The problem isn't so much the ability of the radiators or convectors to heat If the building has been upgraded with better insulation, for instance, it may need less power to keep it warm -- and it was probably overdesigned anyway. Engineers and tradespeople used to do that...

No, there are three problems in any such conversion. The first is is the existing equipment -- in your case the convectors -- suitable for conversion by design? In many cases, particularly if the original installation was a two pipe installation, the answer is yes. But it must be checked. The second is whether the existing piping and other fittings are suitable for conversion? In this case, the answer is almost always no, at least with regard to valves and other fittings. Almost all two pipe systems have some means of controlling steam flow and preventing steam from entering the returns. All of these fittings have to be replaced, as must other steam related fittings such as traps and vents. More obvious, if the original system was one pipe, the return pipes required for hot water heat are completely missing. Then the third question is whether the existing material which can be retained -- piping, radiation, etc. -- can withstand the additional pressure of hot water heat. And the answer there is -- sometimes. Hot water operates at at least ten times the pressure of steam, and weaknesses which were present, but not a factor for steam, may show up -- and usually do.

If you are looking for real life experience, over the years on The Wall what I have observed is that sometimes it works and works well enough. Most of the time it doesn't.

Steamhead

@arborus14 , why do you want to do this conversion? What do you hope to gain, that can't be done by simply upgrading the steam?

LRCCBJ

arborus14 said:

I am working on the heating upgrade of an old building and have just finished the heating load calculations. The building has mostly steam cast iron radiators with some Modine type steam convectors. I have worked out the surface area of the radiators and convectors with Dan's book "Every Dam Radiator" and found the heating load can be offset with water temperatures as low as 160F.

The heating load on the design day could very well be satisfied with 160F water. However, on every other day, you don't even need 160F water.

With steam, we don't modify the temperature suppled to the rads (vacuum systems excepted). We modify the TIME that the steam is provided. If you need a continuous 160F on the design day for hot water, you would need to run a steam boiler for about 45 minutes to accomplish the same goal. At temperatures above the design day, you would run the steam boiler for less than 45 minutes per hour. Tekmar makes a fine product for accomplishing this.

Your costs to convert to hot water, and the inherent risks as stated by Mr. Hall, really do make the conclusion that the current steam system is much more economical to maintain in its current configuration.

arborus14

Thanks for your input. We will likely just upgrade the steam plant. We are finding out that the building has asbestos which will make any distribution piping changes very difficult and expensive. Has anyone ever analyzed existing piping? Some of the steam piping is below grade which adds another possible problem to the project. If it's not in good shape, has anyone used epoxy linings to upgrade existing worn pipes?

Steamhead

@arborus14 , where are you located? We might know someone who can help.

arborus14

Ottawa, Ontario, Canada