Extending Slant-Fin Hot water baseboard

Is there a basement or crawlspace below this room? If yes, it should be a straightforward job except for the fact that it's a gravity system. Adding more pipe increases the pressure drop in the system and could stop flow. I would hear what your contractors have to say about it.

What is the size of the pipe inside the BB? 1"? 3/4"? Whatever it is, don't decrease the size and make sure they properly ream their pipe.

Is the entire system still running gravity with no circulator or is a former gravity system comverted with a circulator?

Regardless, its not the best thing to have baseboard on the same system with CI radiation because they don't heat the same.

A couple of options are to add baseboard but it may not work to your satisfaction. Or take the baseboard out and install a CI radiator.

Is the baseboard on it's own loop or tied into the gravity system?

Pictures will help.

of the boiler and boiler piping from 8' away and pics of the baseboard piping where it connects to the system

It looks like someone put a replacement cover on it, possible without proper hangers to hold the element at the correct height.

you could do a tall one next to the window and a short one under it.

you can buy new ci radiators from us boiler and they aren't super expensive.

Very cool Honeywell Heatmaker!

That still would not be enough heat for this room. Heat loss calculations call for 8000 BTU, but I actually would be perfectly happy with over 9000 BTU for the simple fact slant fin does not hold heat the way a cast iron rad does.

Let's say you are correct that your heatloss for the room is 8000 BTUH. Calculations are notoriously in error, usually resulting in values that exceed the actual loss.

What you're not grasping is that fact that the 8000 BTUH is only necessary on the design day………….the coldest day of the year for your location. The room does not need 8000 BTUH on any other day. So, you MIGHT suffer a small drop in room temperature on that one day. Meaningless.

Your argument for "holding the heat" is not at all relevant. A CI radiator provides both RADIATED HEAT and convective heat.. A baseboard provides only convective heat. The amount of heat necessary for the room is the same.

Where I live, it’s gets below 0° multiple days during the winter, so yes, I need consistent heat to the level of the heat loss calculation. This is why I’m in this position now because whoever did this for the previous owner did NOT do a heat loss calculation and this baseboard is undersized for the room.

Sorry, I misread your original post. The current baseboard is 10 feet and you wish to replace it as its output is approx. 4500 BTUH. I had utilized 7 feet in the original recommendation but this is the value you placed on an additional baseboard.

IF you were to replace it with the recommended H2 baseboard from Smith, its output would double your existing and you will get 9000 BTUH.

The use of the Smith will GUARANTEE that you can maintain 70F on the design day.

This is, by far, the most economical solution and requires the least invasive plumbing. Any additional panel radiators or baseboard that you add will have piping running along the floor. You cannot easily run it beneath the floor. Of course you could utilize a giant panel radiator (24" x 48") but that would need to be NEXT to the window (you don't have 24" below the window with clearance beneath the panel rad) and you'd have exposed copper running along the floor beneath the window to the corner. Of course, you could box it in so it's not obvious, should you choose the panel radiator.

You can use two of the Burnham CR930CFS rads. This pair will give you the necessary output at 170F and they should just fit next to the window (not beneath it). However, I shudder to think of the cost.

You need some serious CI to get to 9000 BTUH.

I don't see how that heats at all. The elements are low enough already and the covers aren't helping. Minimum convection. Let it breathe.

Are you able to get supply and return temperatures for that branch loop? I bet its no more than a 10° temperature difference with the covers on. IDK the heat loss of the room. Maybe it does need linear feet, but those covers look like a hindrance.

Do you have a real heat issue (ie room is too cold all the time) or Man J mismatch? Man J is very hard to get accurate with older houses. I have yet to see a normal sized room that needs 9000BTU even in an old house. Even 4000BTU is a lot for most rooms.

Also mixing cast iron with baseboard is recipe for trouble. You can get around it by adding running the baseboard circulator more and piping it to be able to steal heat from the cast iron rads when the boiler is off.

I'm curious how well that baseboard gets fed with the gravity circulation. the radiators have a lot more water volume to slowly fill and stay hot, the baseboard cools almost instantly, which could increase circulation or maybe it just never gets anywhere near its design temps all the way across.

I'm not sure that wouldn't screw up gravity circulation elsewhere in the system.

Best would be to go back to the full size pipe and put in an appropriately sized CI rad.

Can you get a closeup of them? How wide are the openings on top, 1 mm? I'm sure it's nice and toasty inside the cover.

You can stack Baseray.

Hello Willie,

I hate my hot water baseboard, and I wish we had cast iron radiators just like the ones we had in the apartment over my fathers grocery store that were steam radiators and the steam radiators in my wife's first home where she grew up-this home was a Montgomery Ward kit home that was shipped by railroad car with everything needed to build the home down to the tongue and groove board, nail, paint, asbestos shingle and hand fed coal boiler in one or two box cars.