Must radiator be above main? Heating basement

jlbk

This is probably a dumb question, but can a radiator be lower than the main, but not be a wet return? I have a basement that I would prefer to heat with steam instead of a separate hydronic loop with circulator. Can I hang a radiator on the ceiling or wall below the main but above the return line? Does steam not travel down? I feel like im missing something really simple. Thank you.

bburd

The old-school way to do that, on a gravity return one pipe steam system, was to use a slim wall mount radiator and hang it flat on the ceiling, above the steam main. Rooms heated that way were notoriously uncomfortable.

Steam will indeed go down—many high-rise buildings have steam boilers on the highest floor—but they use condensate pumps. You don’t; so if you install the radiator below the main and the boiler is on the basement floor the radiator may flood with condensate, which won’t circulate quickly enough to give off much heat. Condensate will rise in the wet returns, 2.3 feet above the boiler water line for each pound of steam pressure.

The usual modern solution is to put  that radiator on the floor where it belongs and heat it with condensate pumped from the boiler.

Danny Scully

You could also hang it on the wall and add a drip into the wet returns...far simpler and less to go wrong then with a condensate zone. 

Jamie Hall

The short answer is yes a radiator can be below the main. And they work just fine, on iether one pipe or two pie systems'. There are only three cautions: first, such radiator must be vented. Second, ity will be, ideally, two pipe style (even on a one pipe system)) with the outlet piped to a wet return. And third -- and the real limitation -- is that they must be high enough on the wall or orverhead so that they don't flood from the wet return.

ChicagoCooperator

Don't some people do fin tube on the returns (or is that not really worth it for output)?

Jamie Hall

ChicagoCooperator said:

Don't some people do fin tube on the returns (or is that not really worth it for output)?

Some people do... if you do the math, though, you find that there isn't much heat there.

ChicagoCooperator

Jamie - thanks, that's what I thought.

jlbk

ahh yes the limitation is that it must be roughly 2 feet above the boiler water line. Would a two pipe system circumvent this issue? What about a steam trap? Can steam and condensate pass through the radiator and then have some trap prevent the condensate from entering the radiator?

bburd

Without a condensate pump, gravity head must be sufficient to force the condensate back into the boiler against steam pressure. This applies to one and two pipe systems. An ordinary steam trap is not a pump and will not take the place of one.

Since residential steam systems normally operate at up to 2 psig, returning condensate will stack up to 4.6 feet above the boiler’s waterline. Carrying lower steam pressure, perhaps using a vaporstat, can reduce this.

DanHolohan

@bburd, that’s true if you use a steam trap, but in this case, you don’t need a steam trap. Just vent the radiator and drip it into the wet return. A-dimension of 28” applies from the radiator outlet to the boiler waterline. 

bburd

@DanHolohan Thanks for the clarification. I was not suggesting that a steam trap was necessary; the poster above mentioned it as a possible way around the flooding problem. 

Jamie Hall

jlbk said:

ahh yes the limitation is that it must be roughly 2 feet above the boiler water line. Would a two pipe system circumvent this issue? What about a steam trap? Can steam and condensate pass through the radiator and then have some trap prevent the condensate from entering the radiator?

No. Even if the trap arrangement prevented back flow -- which a steam trap wouldn't -- the condensate in the radiator couldn't get out again.

DanHolohan

What Jamie said. And a check valve would cause the condensate to rise even higher in the radiator. 

DanHolohan

@bburd. Thanks 

mattmia2

What about cast iron baseboard mounted up high and set up as 2 pipe with a vent if you have the wall space? Or even a convector.

Of course both will heat very differently than a traditional CI radiator. The basement itself will be a completely different load than the ground level floor so anything on the same thermostat as the main part of the house isn't going to do a great job of doing more than making it say a workspace. I suppose you could oversize it and use a TRV on the vent to shut it down during some cycles although that would make the having less mass and wanting shorter cycles than the cast iron even worse.

The hot water loop options would give you completely separate control.