3/4" copper loop off 6"(?) pipe former gravity loop: how to increase flow?

Nom_Deplume

In our basement we have big fat (maybe 6") supply and return pipes. At one point 3/4" copper pipes branch off from these and go straight up to the 2nd floor, where they feed a Runtal baseboard in a bathroom. The baseboard does get warm, but the bathroom is colder than other rooms. The baseboard is properly sized for the room.

I'm not an expert, but I'm not at all sure what drives water up to the 2nd floor baseboard. Sure, there is a circulator on the formerly-gravity loop, but the 3/4" loop is long and thin while the formerly-gravity pipes are huge so you wouldn't think much water would divert to the 3/4" pipes. Maybe gravity, rather than the circulator, drives circulation in this loop since there is a 2-floor height advantage.

In any case my question is, how can I increase the flow and will it help to do it? I can put in a circulator in this loop, but it's a long way to run AC from the boiler. Plus, the baseboard has a TRV (now opened wide) and when(if) it shuts off it will kill the circulator. Are there any other ideas? many thanks,

Don_197

is there any way to restrict flow on the larger supply pipe just downstream of the 3/4" takeoff? (I doubt it....that would be a BIG VALVE.....never hurts to ask) other than that.......you could but a circulator on that loop...........the smallest wimpiest one you can find. Be careful!! messing with a converted gravity system can have LOTS of unforeseen effects on the rest of the system.

Ironman

Properly Sized - Maybe not.
It may be properly sized for the heat loss, but not proportionately sized to the rest of the system. The old CI. Rads are probably well over-sized since the house has no doubt been tightened up in more recent times. Also, those large rads required cooler water than what the Runtal does (unless it's over-sized). So, in all likelyhood, the Runtall and the pipes are under-sized.
You could add a Grundfos Alpha circ which would sense when the TRV opens, but that would not cause the boiler to fire.
The surest thing would be to pipe the loop all the way back to the boiler and put it on its own pump and stat. In other words, make it another zone. But, unless you have a C.I. Boiler that's high mass, creating a micro zone may cause the boiler to short cycle.
How about posting some pics and more info about your system?

Nom_Deplume

Thanks for the replies. Shutting off the downstream rads is a good idea, I just did it (only one rad there, actually) and I'll find out.

Runtal baseboard is slightly oversized, yes, relative to the CI rads in the other rooms. I checked the numbers myself. Yes, a separate micro-zone would not be a good idea but it doesn't have to be a separate zone, one can run multiple circs in parallel as a single zone. I'll think about doing that but it's a lot of work. I'm hoping that turning the downstream rad down will do it.

icesailor

"" Runtal baseboard is slightly oversized, yes, relative to the CI rads in the other rooms. I checked the numbers myself ""

"Oversized" in relation to what?

Did someone do a complete and total heat loss on the building then room by room? Then, measured each and every radiator in each room and compare the output to the installed radiation and loss? Its my understanding that the really old gravity systems were designed for 160 or 17 degree water. What temperature output was used to calculate what Runtal was used? Runtals are "Convectors. Cast Iron Radiators in old gravity systems "radiate", not convect. Not the same thing.

If it is a gas fired boiler without a tankless coil like you might get if it was oil and hot water, Outdoor Reset might make it work better, but that would only be to get the Runtal as hot as the rest of the radiators.

Without seeing the application, a Taco "I" Series 4 way Mixer, properly connected and using the ODR feature would give you a lot of nice comfort and would probably pay for itself quickly.

If you don't want to really spend a lot of money, put a fan Light heater or an electric heater in the bathroom on a timer. The cost will be a lot less and you aren't spending a fortune to try to make the bathroom warmer. There's never enough light in most bathrooms. Especially in old houses. You weren't supposed to be comfortable doing something that wasn't talked about in parlor conversations. Bathrooms should be the most comfortable room in a house. Every bathroom should be required by code to have a great big bright light shining down on the toilet. For reading in comfort. Reading on the best seat in the house.

FranklinD

We went through that. We have 3/4 takeoffs to radiators on a converted gravity system.

My first thought was 'is there a pressure drop through a TRV even in the open position?' that might be impeding flow since it's not 'directly' pumped?

And my second thought was this: we tried a 'towel warmer radiator' piped in place of a cast iron radiator in our bathroom. It warmed up, but our system maxes out around 140-150* water at -10f outside. The towel rad just didn't warm the room. So we sourced an old, small cast iron radiator. Works MUCH better, since it hold the heat (300 lbs of mass). If the Runtal baseboard works by convection and your water temps are like mine, it's won't work well. You need to radiate, not solely convect.

I run 6.8 gpm thru my system, the mains are around 3" or so, reducing 1/2" at each pair of run-outs. I get plenty of flow to each rad once I got some radiator valves freed up and adjusted properly (thanks icesailer!). An IR temp gun was invaluable for balancing.

Best of luck!