CI Radiators, converting iron pipe to pex

vincyking11212

Hi, I’m trying to do steam to hydronic (hot water) conversion and need some advice before installing next month. I bought a 7 section manifold to feed 6 CI radiators and 1 hot water heat blower, a navien NHB-55 (Mod con boiler), and running Homeruns 1/2 inch pex al pex. However I am concerned about my design. I am converting the entire house from a 140k BTU steam heat system with DHW to 2-Navien mod/con with single zone use. My house heat loss is 20k and the radiators will output collectively 29,700 btus and all of the runs are about 45 feet long. Also, I'm installing one boiler per unit, it is a duplex house. Any suggestions?

Steamhead

I think you're wasting your money. You might gain 2-3% efficiency, and the Navien won't last anywhere near as long as a cast-iron boiler. And some types of radiators won't work with hot-water.

Jamie Hall

Keep the steam, if you haven't already demolished it.

First, it will be less expensive.

Second, it will be a lot less work.

Third, it will heat better. Particularly, in that regard, have you determined whether the steam radiators -- which may or may not work for hot water -- will produce enough heat? At best you can expect only half to maybe two thirds as much heat from a given radiator on hot water as you got from steam.

Forth, have you evaluated what size boiler or boilers you really need? Steam is sized on the basis of the installed radiation ("EDR"). Hot water is sized on the basis of the heat loss of the structure.

vincyking11212

I already wrecked out the steam and oil tanks. I brought CI rads. What are the usually issues with using CI rads with a hydronic setup?

Steamhead

If the sections of a radiator are only connected across the bottom, rather than at both top and bottom, water cannot circulate through them.

You would have done much better to consult with us before tearing everything out.

vincyking11212

Its not too late for me to make the adjustments, I haven't installed the new rads yet. Do you think it is better to install the supply on the top radiator connection and the return on the bottom radiator connection (left to right)

Steamhead

Take some pics of the rads you have and post them here.

vincyking11212

Rads.

STEAM DOCTOR

> @vincyking11212 said:
> Hi, I’m trying to do steam to hydronic (hot water) conversion and need some advice before installing next month. I bought a 7 section manifold to feed 6 CI radiators and 1 hot water heat blower, a navien NHB-55 (Mod con boiler), and running Homeruns 1/2 inch pex al pex. However I am concerned about my design. I am converting the entire house from a 140k BTU steam heat system with DHW to 2-Navien mod/con with single zone use. My house heat loss is 50k and the radiators will output collectively 29,700 btus and all of the runs are about 45 feet long. Also, I'm installing one boiler per unit, it is a duplex house. Any suggestions?

Your heatloss is 50k and radiator output is 29k??

vincyking11212

@STEAM DOCTOR that was a typo, the approx. heat loss is 20k. The house is attached and insulated.

vincyking11212

Also, it is a small building that is apporximately 1000 sq ft.