Radiator Question

amhplumb_2

Belated thanks Brad, started to the same day and called away from the screen, in my mind I did it, crazy month! The job is working out well. Doing it sections at a time off of new header using 1-1/4 (vs the 2-1/2"!) and P/S pumping. The customer was amazed seeing 3/4" replacing 1-1/2 to one of the rads! Good ol' gravity sizing! The TRV on the huge rad in the living room eliminated temp swings in the room!
Al

amhplumb_2

Radiator sizing question

Fellow Wallies, what factor do you use for equivalent foot/feet, for radiators when calculating head loss in sizing the circulator & the piping? My IBR tables only have for baseboard, and I have never sized for rads before! Are there tables, a formula, or a rule of thumb? I have a project where I am replacing a boiler and re-piping an old gravity converion system in which the piping is now way oversized. Fortunately my customer wants to keep the rads! My heat loss calculations show the rad's to be right in the ballpark all over a bit! Thanks!

Brad White

Pressure Drop of Old Cast Iron Radiators

Negligible. Think of 1.0 GPM flowing in a 3/4" pipe. Head loss somewhere above Paris Hilton's dog's IQ. Easy to deal with.

I mean the head loss.

Take that same flow. Think about is as being put it into a large room at very low velocity... even with a TRV, assuming 0.25 feet of head is pretty conservative.

Bottom line: If you are using a TRV and know the flow rate (you should do both IMHO), then take the TRV delta-P and add ten percent to it. Sleep well.

If your radiator to heat loss ratio is high (as it nicely so often is), you are doing a service to the Owner. Outdoor reset and old cast iron is a marriage of love.