Can I pipe a cast iron radiator from one side only?

Question

I am installing a new cast iron radiator to heat my garage using hot water. The radiator has two ports on each side; one on top and one on bottom.

(OCS Part Number T41912)

Normally, such a radiator would be piped to the bottom ports on both sides when using hot water, and the top ports would be plugged.

Due to a space constraint, however, it would be beneficial if I could use the top and bottom ports on one side, with the other side completely plugged off.

1. Is this okay to do?
2. Will it still heat effectively?
3. Should the supply line enter top or bottom?

Answer 1

If you have a installation manual for it check that, it should list the possible hookup configurations.

I've personally never seen one of those with both sides on the bottom, I'll always seen them always with inlet at the top and return at the bottom.

If you can hook it up at the top, then you can hook up the supply and return on one side only.

However you still need a bleed nipple on the other side of the top inlet. Air will collect in that thing and you need to be able to get rid of it. If you have room for a bleed nipple then you most likely have room for the return on that side.

Answer 2

1. Is this okay to do? Yes.

2. Will it still heat effectively? Yes; it won't be optimal, but the difference is not worth obsessing about.

3. Should the supply line enter top or bottom? This almost doesn't matter in terms of heating if there's no air in it and flow rate is correct (slow) and radiator and piping is sized properly.

   More important will be the radiator's location and the existing piping, as this will affect (a) how you fit it and (b) the appearance after installation.

   Optimally, in terms of heating effectiveness, the supply should enter at the top and return out the other side bottom because of hot/cold buoyancy (so that the colder water exits from the bottom return). If air is in the radiator, which will affect heating effectiveness the most, then in the bottom and exit out the top would be preferable if you never check on the air bleed on the radiator.

You can easily verify (today) using a cheap IR temperature gun (on cast iron it will be quite accurate) to check temperature difference across the radiator as the hot water flows through it. If the supply pipe to the radiator is X° and the entire radiator and the immediate exit piping reaches the same X° within a reasonable time before the heat cycles off then you can't do any better than that.

If you really care, hook up a hot water hose to the radiator outside and play with it there first. You didn't mention make/model and where you got it: if it's a legitimate make from a credible seller then okay; if purchased off Amazon and shipped from Hong Kong, then it wouldn't surprise me how poorly its piping could be or if the thing is half fake.

Answer 3

It should be fine. The two important things you need to ensure are that:

1. The outflow pipe is connected to the bottom of the radiator. (It doesn't really matter whether the inflow pipe is connected to the bottom or the top, since hot water rises anyway. But if the outflow pipe is connected to the top, it will let out the hottest water in the radiator rather than the coldest.)

2. There are no internal baffles or other obstacles that would prevent the hot water from flowing into the top ends of all the columns and the cold water from flowing out of their bottom ends. (Apparently some radiators designed for a bottom-to-bottom connection may have such baffles installed at the bottom, even though they really should not be necessary.)

Since you have the radiator disconnected from the pipes, the second part should be easy to check: just look into one of the top ports and check that you can see all the way through the radiator to the other top port. Or try pushing something like a curtain rod in through one of the top ports and out the other and check that it goes through without hitting an obstacle. Then repeat the same check for the bottom ports.

Also, as noted in the other answers, if your radiator doesn't have a built-in air bleed valve, you'll need to install one to at least one of the top ports. It doesn't really matter much which one; the air bleed valve can share a port with the inflow pipe but doesn't have to. What's important is that the bleed valve must be at the highest point of the whole system where air bubbles will collect. Ideally you should mount the whole radiator at a slight angle, so that the end with the air bleed valve is slightly higher than the other end.

Finally, once you have the radiator hooked up and working, it's easy to check whether it's heating evenly with a thermal camera or an IR thermometer. Basic thermal cameras can be found for under $100 nowadays, while IR thermometers (which are basically just single pixel thermal cameras) may cost as little as $10. Or, in a pinch, just touch the radiator with your hand and check that all of its four corners feel reasonably warm. It's normal for the bottom side of the radiator to be cooler than the top side since, again, warm water rises and cold water sinks. But if one of the bottom or top corners feels noticeably cooler than the other, you may have some kind of water circulation issues.