Can I mix cast iron radiators and cast iron baseboards in same hot water heat system?

eclecticmn

I have an old house with old cast iron radiators and boiler temp around 180 deg F, if that matters. I ripped out the kitchen slant fins as they never heated the kitchen. I am about to put in two 26 in high 8 section cast iron used radiators in front of a double window in the niche. They do stick out some and above the window bottoms.

I only recently learned that cast iron baseboards existed and just saw some used on craigslist, but too expensive as listed. Can I mix these in the system? Can you wall mount these?

It is one zone for the whole house with a two pipe system I think it is called. Two large supply lines leave the boiler and two large returns go back to the boiler. They both decrease in diameters further from the boiler. I control heat by throttling back the flow in some rooms I do not use.

Jamie Hall

Well, you can mix them, and the cast iron baseboards do behave more like the regular radiators. They don't have, usually, as much heat output -- simply because they don't have the total surface area. They will work much better, though, than the finned sort.

It sounds as though your system may have been a gravity system, once upon a time. In which case your approach to balancing -- by reducing flow through radiators which aren't really needed, or needed as much -- is almost the only way to do the job unless it is much more extensively rearranged.

EBEBRATT-Ed

@eclecticmn

Fin tube and CI heat and cool at different rates. Using them on the same zone isn't recommended. CI takes longer to heat but stays hot longer fin tube heats faster and cools faster

eclecticmn

I ripped out the slant fins and gave them away as they never heated the kitchen. I am about the plumb in two cast iron radiators but wondered if I could mix cast iron base boards with the hot water cast iron radiators in the rest of the house.

Jamie Hall

A rather important question is why didn't the finned units provide heat? As I noted in my previous comment, you may have a converted gravity system and simply not be getting circulation in them. The cast iron baseboards are a better fit with the rest of your radiation -- but if they don't get enough flow, they won't heat much if any better.

eclecticmn

Why the slant fins did not provide heat is a mystery. I have asked several places. I examined many things and replaced things. I replaced the slant fins and valve and made sure I had elbows with bleeders on each end to fix any air lock. The slant fins and elbows were the highest point on that loop, low on the first floor kitchen. The 2 1/2 in main teed off to 1 inch then 3/4 bushing then 3/4 copper to the slant fins, which were first in line after which the the 2 1/2 main dropped in size. I could find no corrosion or blockage. I am using new plumbing in part because the old plumbing was jammed into a tight corner inside a basement wall.

Every other radiator in the two story house works fine. The new plumbing will be from the 2 1/2 in main to 1 inch O2 barrier pex to 1 inch copper to 1 inch hot water radiator valve to 1 inch bushings to two cast iron radiators in series then back to the 2 1/2 in return main line to the boiler.

If that does not work I will consider installing a circulator pump in line in that loop. The previous owner recently told me the kitchen did not have working hot water heat for at least since 1989 when he moved in so he installed a wood stove!

You mentioned this was maybe a converted gravity system? Maybe no circulation? Why not?
What does that mean? Is there some strange way where the return main has too high a pressure to allow flow back? I cannot imagine how that could happen.

I am attaching a rough piping diagram. The pipe sizes off the mains might be off by 1/4 inch. The returns are alongside the supply and the piping is the same. The boiler is the lowest point, in the basement. The boiler feeds in where the words West and East are. West and East join up right near the boiler.

eclecticmn

Re an old gravity system. My hot water system has a newer boiler in the basement with a maybe 1 foot diameter by 3 feet long horizontal ballast tank (no diaphragm) above the boiler near the basement ceiling. No other water tanks.

Jamie Hall

Your first paragraph and the drawing solves the mystery. Remember that water is lazy. VERY lazy.

Now look at your pipe sizes. You have a beautiful big 2 1/2 inch main for the second floor, with various risers going off of it -- ranging from 1 1/4 down to 3/4. Now -- very roughly, the flow resistance in a pipe varies as the square of the pipe diameter and the flow through it. All those risers had to have the same flow resistance -- that's one of the rules. A 3/4 inch pipe will, for the same flow, have twice the resistance of a 1 inch for the same length, and 4 times the resistance of a 1 1/2 inch line. In addition, the fin tube has far more resistance than a nice big roomy radiator. So... your fin tube just wasn't getting enough flow to generate much heat.

What needs to happen is that you need to have valves on the bigger lines to increase the resistance, so the flow will go through the smaller lines. They are called balancing valves, and they really are needed on systems like this.

EBEBRATT-Ed

@eclecticmn

@Jamie Hall is exactly right. Water takes the path of least resistance. Your system was sized for gravaty flow with no circulator. The pipes are huge.

You can't add small pipe to that system and expect it to work....it won't water takes the easiest path.

You have two choices:

1 Put balancing valves in the large old pipes to force some water through the new zone.

2 or put a circulator on the new zone

#2 will be less$$ and you can put baseboard or anything you want back in.

eclecticmn

Jamie Hall: Thank you. You are the first person in many posts here and elsewhere to mention this. This even after I included the drawing. BTW my piping diagram pipe sizes may be off by 1/4 in as I measured in a hurry and made some mistakes. The 2 1/2 in mains are all in the basement feeding the first and second floors. It is possible that the largest pipe leaving the mains is 1 inch steel/iron, not 1 1/4 in. The pipe leaving the 2 1/2 in main for the kitchen is 1 inch steel/iron. It was reduced to 3/4 with a bushing before then to 3/4 copper for maybe 20 feet to the slant fins. I ripped it all out in desperation. I valved it off so I can screw around with it in winter.

My current plan is to run a 1 inch O2 barrier pex from the 1 inch steel to the 1 inch copper near the cast iron radiators to the 1 inch radiator valve and bushings. I understand the pex B is .875 ID vs .995 ID 1 in copper vs 1.049 in ID sched 40 iron vs 0.785 in ID 3/4 copper. The pex B fittings will reduce the flow but only for a short distance, not the whole length.

I assume that the flow restrictions from narrow pipe and fittings is cumulative with length. One fitting that is small will not kill everything.

I am not a professional and do not have tools for pex A which might create less flow restriction. Maybe 1 inch pex A with fittings would create fewer restrictions???

It is winter in MN and there is a limit to what I want to take chances with.* Long story. Maybe in spring I will try an optimal solution. What is that? Also, the upstairs radiator valves may restrict the overall flow to encourage flow to the kitchen.

Is a Taco circulating pump in line for the kitchen loop a possible fix if my fix does not work?

*Years ago I replaced all the radiator valves at once and needed ventless gas heaters to save myself from frozen pipes for a couple weeks. I hesitate to remove the tee off the 2 1/2 main (to line it up) for fear of cracking something ancient.

Jamie Hall

I understand your caution. Middle of winter is no time to play games with a heating system in Minnesota.

I think you may still have balance problems, but if you have functioning valves on the other radiators try closing them some to see if you can persuade the water to go where you want it to. Don't be too shy with this -- you may well have to get them half closed or even more to see the effect you want.

And yes you can put a booster pump on that circuit to help with the flow.

eclecticmn

EBEBRATT-Ed said:

@eclecticmn

@Jamie Hall is exactly right. Water takes the path of least resistance. Your system was sized for gravaty flow with no circulator. The pipes are huge.

You can't add small pie to that system and expect it to work....it won't water takes the easiest path.

You have two choices:

1 Put balancing valves in the large old pipes tp force some water through the new zone.

2 or put a circulator on the new zone

#2 will be less$$ and you can put baseboard or anything you want back in.

Thank you. I cannot imagine trying to even get at the old large 2 1/2 pipes or even the smaller ones down stream. Increasing the kitchen loop pipe size to 1 inch and the radiators to one inch valve cast iron might help. It was 3/4 copper and 3/4 copper slant fins.

If I was skilled I might be able to use 1 inch sched 40 or even larger. As I am not I am stuck with pex and copper.

bburd

There is another issue here: cast-iron radiators hold a large amount of water, unlike fin tube or even cast-iron baseboard. That water has immense thermal mass, so those cast-iron radiators will stay hot for a long time after less massive types of radiation have cooled to room temperature. I once owned a house like that myself.

Boiled down: A single thermostat zone should have the same type of radiation throughout. You will be happier with cast-iron radiators in your kitchen.

EBEBRATT-Ed

@eclecticmn

If you have a place you can tie in a 3/4" supply and a 3/4" return you can use copper or pex and a circulator to run what you need.

Maybe even 1/2" depending on what you are doing.

Why not post a picture of your boiler so we can see what is there

pecmsg

1 thing to remember. That kitchen has 2 different heat loads. 1 while sitting 1 while cooking. While idol the base and upper cabinets add extra insulation to the outside walls. I removed a Cast Iron rad during a remodel. In turned gained a lot of counter space. Installed a Kick Space fan unit in the bench seating. Works great but had to put a t-stat open on rise to shut the fan down while cooking large meals.

eclecticmn

EBEBRATT-Ed said:

@eclecticmn

If you have a place you can tie in a 3/4" supply and a 3/4" return you can use copper or pex and a circulator to run what you need.

Maybe even 1/2" depending on what you are doing.
,
Why not post a picture of your boiler so we can see what is there

Would I put a circ pump on the supply side, I assume?

I can get at the 1 inch tee from the 2 1/2 main and I valved them off with expensive threaded ball valves so I can mess with the loop in winter. There used to be a bushing reducing to 3/4 followed by 3/4 in copper to 3/4 in slant fins.

I will try to plumb in 1 inch O2 barrier pex for now. I wanted minimum flow restriction. Maybe add a circ pump in spring. Right now the 1 inch pipe nipples lines are kinda crooked. I would like to allign them before I install a circ pump. I do not want to tempt fate now. Perhaps I could put in a circ pump temporarily in line with the 1 inch O2 barrier pex.

eclecticmn

pecmsg said:

1 thing to remember. That kitchen has 2 different heat loads. 1 while sitting 1 while cooking. While idol the base and upper cabinets add extra insulation to the outside walls. I removed a Cast Iron rad during a remodel. In turned gained a lot of counter space. Installed a Kick Space fan unit in the bench seating. Works great but had to put a t-stat open on rise to shut the fan down while cooking large meals.

Interesting. I found 3 26 in high cast iron radiators, 8 sections each, 5 tubes. I planned to place all 3 under some double windows but that will be a tight fit and not allow for unions so I will install 2. I may place the third, LATER, under a more remote kitchen window BUT that plumbing would be through a crawl space AND any piping or wiring too close to the wall is above an approx 14 inch concrete wall and must extend out.

The toe kick heater is interesting. I assume that would use the same temp hot water as the radiators. I assume there are other such hot water heaters with fans. My goals are low for now. The kitchen has a door to a drafty pantry that has a door to the outside. Also a dog door to the pantry and another to the outside.Any solution better than the wood stove and leaving the oven on would be great.

Off topic but I recently learned of, bought, and used a toe kick saw from Harbor Freight for another purpose. Luckily I still have all my limbs.


When scrounging around the local high priced salvage place I came across some old heavy duty iron benches with small radiators inside.

EBEBRATT-Ed

@eclecticmn

I am afraid your missing the point. The old system was designed for gravity flow with no pump and had large sized pipe. If you run 1" with no pump you will probably get 0 flow. The same problem you had before. The old system worked by gravity and the water took the path of least resistance. Now it has a pump on it the water will still take the path of least resistance and little or nothing will flow through the new zone.

If you want it to work your going to have to put a dedicated pump on your new zone

eclecticmn

Other loops off the 2 1/2 in main have 1 inch pipes and cast iron radiators and get hot. I am hoping that changing the kitchen to a 1 inch line with cast iron radiators will help (over the old 3/4 pipe and 3/4 slant fins). If not enough help I will add a pump to that loop. I know that the O2 barrier pex with fittings will restrict some compared to all iron 1 inch.

I thought some pipes in other loops were 1 1/4 inch but I might be wrong. I was wrong about one for sure. They might all be 1 inch.