wrong mix of low temp cast iron & hi temp copper fin rads

John_182

Hi, my 90 yr old house originally had gravity upfeed hot-water heater. I confirmed this in the Systems part of this website. Over the years it was modernized with a circulation pump, compression tank, living room rads replaced with full wall length baseboard rads, and in 1991 with a Dunkirk's Plymouth Water (PWB4) Boiler, and a second zone for the finished basement. I took over in 1998.

When the second zone was added (1991) they used hi temp copper fin baseboard rads. These throw off almost no heat although hot water is circulating. My understanding is that this is because they require much hotter water than the rest of the system which has a mix of chunky old cast iron rads and the older style wrap around the room baseboard rads.

Presently the boiler is piped very simply with a single supply and return that splits to two circulation pumps for the two zones. Basement zone runs nonstop with no thermostat or control over boiler, partly to avoid any issue of thermal shock to boiler since there is no bypass or primary/secondary. In the past basement zone did have thermostat and control over boiler but we had a problem with this inducing flow in main zone even when main zone didn't call for heat. Backflow preventer values were added to the main loop, but these constantly tinkle unless main control value is turned down to perhaps half the flow.

My first (of many) question is: What should I do to get heat in the basement zone?

Various contractors have suggested just about everything:
- install electric rads in the basement and ignore hydronics in basement, supposedly least expensive option
- replace basement copper fins with old style cast iron
- replace basement copper fins with low temp baseboard rads
- repipe boiler to allow for two temps of water to two zones
- etc

Can anyone help me figure out which of these would be the best approach?

Glenn Sossin_2

Copper/Alum Fin not putting out.

As long as you don't mix the copper fin and cast iron on the same loop, you should be ok. They have different densities, hence, a different response curve. The cast iron takes longer to come up to temperature - once it does, it takes a longer time to cool down. It characteristically has a much flatter wider heat curve, resulting in a much smoother room temp changes than alum fin baseboard.

Your comment "These throw off almost no heat" - is most likely the result of a very minimal flow rate. This could be the result of a multitude of factors - air, flow restriction, imbalance of flow with the other zone, a bad circulator .....etc.

Your comment "My understanding is that this is because they require much hotter water than the rest of the system" isn't exactly true. Radiators don't actually require a certain temperature to work. The manufacturer will usually publish a chart with varied output numbers based on water temps as low as 110F and as high as 230F with flowrates of 1gpm(500lbs/hr) and 4gpm 2,000lbs/hr).

The heat they radiate is a primary function of two things - flow rate (gpm), and water temperature. These two values determine how much heat energy (btu's) the baseboard (or any other type of radiation) puts out.

Another big factor/variable sometimes overlooked - we need the ability to convect air across the element inside the cover. If the elements are dirty, caked up with crud/crap/dust, fins bent and mangled, this could have a substantial impact on the heat output of the baseboard. Pop off the cover and take a look at the fins. Are they relatively clean?. Is the damper opened properly. Is there an air gap on the bottom of the baseboards so air can get inside?? Sometimes people put in new thick pile carpeting that will virtually close off the bottom of the board opening. I would suspect the heat output would be 30% -40% of the normal rating if the air isn't able to convect freely.

Actually, you'll probably be surprised to learn, for a new install, at a given flow rate and temperature, your aluminum fin board would probably have a slightly higher output rating than the cast iron baseboard. Why ? More surface area to transfer heat to the air - those fins and the convective currents

Try to see the temperature difference between the supply and return pipes on the baseboard loop. If its low (6-12F), that indicates you probably have a good flow, but limited transmission from the boards. This could be because the elements are dirty and or there is inadequate flow through the baseboard itself.

If its high/wide 25-30F or more, that would most likely indicate a very low flow rate. The board at the beginning of the circuit is probably hot, but as the water travels down the piping, it's giving off it's heat energy and cooling down to the point where near the end of the loop, the water isn't really hot enough to generate sufficient heat.

I'd be curious what your find. I'll be watching for your response.

tim smith

mixed radiation

I would say the easiest way would be some repipe & wire change at boiler so either zone can call for heat. Protect boiler from thermal shock and verify baseboard radiation is enough for area. I would do this first. You can run both at same temp as long as baseboard can do the job with the amount in place. Good luck, Tim

John_182

What is the best way to measure the temp of the supply and return for the basement rads? I have a medical (mouth/bum) thermometer, an outdoor drybulb therm, and an indoor dial therm. I can't quite see how to use those, or can I get something better at the hardware store?

tim smith

Thermometer

Probably not at the hardware store but you need a surface contact probe, usually a digital meter with probe for testing surface temps. Wraps around pipe w/ velcro strap with a disc type thermistor against pipe. Or a infrared gun. Good luck, Tim