cast-iron radiator temperature drop

bruce smith

yeah, i know how many many square feet of edr and corresponding flow. maybe i phrased the question wrong. can i safely use a 20 deg. delta t w/radiators? bruce

bruce smith

temperature drop through a cast-iron radiator

wondering what the delta T is through a column type cast-iron radiator. more specifically whether to use a single pipe system with monoflow T's (which have terrible flow rates) or a reverse return system which uses more pipe and labor? if the temp drop is large enough through the radiator the poor flow through the monoflow tee isn't as critical. i know they used to use 1 pipe systems w/cast-iron radiators just can't find the right info.

Brad White_203

All of the usual variables apply.

Delta-T is just a function of flow, radiator surface area and ambient around the radiator, basically. Can be one degree or 60 degrees.

I would take exception to your statement that "monoflow t's have terrible flow rates". It all depends on what the delta-P through the radiator. I would agree that small-bore fin-tube, long branches, down-feeds without dual Monoflow tees can challenge the flow rates in any case.

But large volume cast iron has minimal pressure drop.

So, do you know your flow rate, heat loss, radiator surface area (EDR) and desired room temperatures?

Brad White_203

Oh gosh yes

Any delta-T you want, so long as your boiler can handle the return temperatures which result.

Cast iron is ideal in many ways.

bruce smith

thanks. we'll b using a condensing type boiler w/160 deg supply temp which means 130 btuh/sq ft of radiation.

Brad White_203

Perfect

And not that you did not already do so, but double-check your heat losses versus your radiation EDR. In actual practice you can likely use a lower "high end" temperature than you may think you need.

Go with as aggressive a reset schedule as you can (trim to comfort of course!) and enjoy the savings.

TRV's on the radiators with an ECM circulator, that is icing on the cake.