1 pipe steam wet return line not getting hot

deebster190

Hi, I have a 3 floor multi family semi-detached house that has the steam boiler in the back 1/3 of the house in the walk in basement. Everything works fine, heat is going upstairs, boiler shutting off on pressure, thermostat is working fine, however the front of the house wet return line that runs along the floor is not getting hot even after 1 hour of the boiler running (it is the the return for the front 2/3 of the house from the boiler). I know the water feeder works and it's not constantly feeding due to loss of water not returning to the boiler and the return line isn't stuffed up bec A. Feeder is not constantly feeding and B. the the radiators upstairs aren't pissing out water from the air valves being that it cannot return.
The back 1/3 return line of the house does eventually get hot, but takes an extremely long time, about an hour.

Any help with this is appreciated

TIA

Jamie Hall

Wet return? Along the floor? The only reason it would get even warm is if enough hot condensate got into it. And, of course, condensate is supposed to get in there -- but enough to get it hot? Slightly warm perhaps, if it takes the condensate from a lot of radiators...

Suppose you have a radiator putting out about 10,000 BTUh. That works out to a bit over a gallon per hour of condensate. That will just barely fill a 2 inch pipe 10 feet long -- during which time it is mixing with the water in the pipe and cooling. It might -- if the return is only ten feet long -- get up to 120 or so... in an hour...

Why do you think this is a problem?

deebster190

If I were to want to put a hydronic loop off the return line and maintain it with a aquastat at 140 degrees, then wouldn’t the return line need to be able to reach that temp?

Jamie Hall

deebster190 said:

If I were to want to put a hydronic loop off the return line and maintain it with a aquastat at 140 degrees, then wouldn’t the return line need to be able to reach that temp?

This idea comes up from time to time, and it does sound attractive. Unfortunately, it doesn't work. There simply is very little -- by comparison -- residual heat in the condensate from steam systems.

Go back up to my calculation above. We found there was perhaps a gallon of water per hour. That's around 8 pounds of the stuff. If we suppose that that condensate, when it left the radiator, was at 200 F, and that by the time it got back to the boiler it had cooled to 100 F -- a delta T of 100. That's 800 BTUh that that condensate will give you.

Which is about the same as a couple of hundred watt bulbs.

It's perfectly possible to put a hot water loop running off the boiler in the basement -- but not using the condensate.

JUGHNE

Feel good that the CI rad has milked all the heat it could out of the steam and put it into the living space. Just put your hand on the main and then the wet return to feel (carefully) the difference.

ethicalpaul

That one degree of change from steam at 212 to water at 211 contains a lot of heat energy. The water going from 211 to room temperature doesn't contain very much. It's not that much water and there is a lot of cold water and pipes in a wet return for it to mix with.

deebster190

Thanks all for your help and advice. Gonna put the loop through the boiler and put an aquastat on the loop. 

Would you put it on the supply or return side and at what temperature? 

Jamie Hall

You should use a tapping as low as possible on the boiler for the supply, and pump away from that. The return line can go -- and perhaps should -- into the wet return.

The aquastat setting -- which would be on the supply line -- should be whatever it takes to heat the space to the temperature you want with the radiation you are using.

ethicalpaul

The lowest tapping? There's not always a choice, but I'd take a higher tapping than the lowest to minimize the mud getting sucked through the pump.

Here's how to do it: https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

Jamie Hall

ethicalpaul said:

The lowest tapping? There's not always a choice, but I'd take a higher tapping than the lowest to minimize the mud getting sucked through the pump.

Here's how to do it: https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

Well, true on the mud -- but whatever tapping is used, it must be low enough to ensure that the pump always has a decent net positive suction head on it.

ethicalpaul

I agree. Question: can you tap from a bit higher (but still well under waterline of course) and then run it immediately down to the floor to get that additional head on it?

Jamie Hall

ethicalpaul said:

I agree. Question: can you tap from a bit higher (but still well under waterline of course) and then run it immediately down to the floor to get that additional head on it?

Yes -- that works fine.