Home>Discussions>PLUMBING>Old, cast iron radiators vs Slant Fin radiators
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1917house
Old, cast iron radiators vs Slant Fin radiators

Hi, I recently got a crazy idea to convert electric baseboard heat to hot water radiant heat. To make a long, complicated story short, can anyone enlighten me on the impossibility or advantages of installing old, cast iron radiators versus installing newer Slant Fin radiators. I've heard the Slant Fins are the least expensive to buy but the most expensive to heat with. I recently purchased some beautiful old radiators but it's tough finding anyone who wants to hook them up in a house that's never had them.
Thanks.

johnjh2o
Re: Old, cast iron radiators vs Slant Fin radiators

The easiest hot water system to install is a loop system. That can be used with copper fin baseboard such as Slant Fin. With this type system there are no main lines it just loops from one section of baseboard to another. With cast iron radiators this type system can't be used because the water would cool between radiators. When using radiators the two systems that are used is a one or two pipe system which requires mains to be run around the basement which is much more costly then a loop system. I don't think you would see much of a difference in operating cost between the two systems. But the radiators would be a much quieter system.

John

brewster
Re: Old, cast iron radiators vs Slant Fin radiators

Cast iron rads are an EXCELLENT way to heat a home; however, there are caveats; you note you have an older house---how many total square feet; how many rads did you buy, have you had them air-tested to 30 psi to check for leaks (can easily be done with simple fittings & bicycle pump), are they free of rust & have you calculated their EDR heat output in BTUs/hour (site below); are the rooms large w/large windows & ceilings higher than 8' ?????

If there is any rust on the newly bought rads, they can be taken to an auto body shop to have them sand-blasted & repainted to come out looking like new; you will have to find some way if they are sitting in the yard to move them around, up the stairs, into the house.

Your first step should be to check the exterior walls & attic for adequate insulation---have cellulose insulation blown in to all exterior walls & attics & change to double pane vinyl windows if you have leaky, old single pane windows.

In your part of the country there may not be a lot of heating installers who are familiar with installing cast iron rads; then again, many don't want the responsibility of taking the chance of installing 2nd hand rads if there is a chance that they may develop a leak sometime down the road---in such a case removal & replacement of another cast iron rad for the leaker can be a real hassle----many of these rads weigh in excess of 300 lbs & hauling them up & down stairs can be a real PITA.

If you can find someone to do the install, it's possible to mix them with baseboard radiation, which is much easier to handle & install; baseboard comes in standard output of approx 580 BTU/hr per foot, or high output baseboard at approx 850 BTU/hr per foot; the rads should be placed directly under a window---the great advantage of a CI rad is that it holds the heat from the HW a lot longer (typically for an hour or so) than a strip of aluminum finned baseboard (typically for a matter of minutes); the rad keeps on pumping out convective & radiant heat, so it complements the quick response of the baseboard when used in a room in combination; it also serves to dampen the cold air coming off the window for a more comfortable room---can make for a very comfy living room, which is where most people spend most of their time; you will have to Google "Heat Loss Calculation" to find a formula on how to calculate the total BTU/hr heat loss for each room, & the total Btu OUTPUT of the rad & any baseboard (approx 580 BTU/hr per foot of baseboard) combination-----the total heat output in BTU/hr must equal or exceed the room's total HEAT LOSS per hour at or near "design temperature", which is temps during the coldest days of the year.

There are other types of convectors you can use---stainless steel panel wall radiators have become popular (site below); they are much lighter than CI rads, are very attractive, & put out a lot of heat, many of them are pricey though.

Google "How to install Hydronic Heating"

John Siegenthaler is a hydronic engineer that has written much on baseboard & rad installation techniques; Google "Baseboard Makeover Siegenthaler", "Beyond Series Circuits Siegenthaler", "The Glitch & the Fix Siegenthaler". His excellent book "Modern hydronic Heating" is in some public libraries.

http://highperformancehvac.com/boiler-water-loops/
http://www.antiqueplumbingandradiators.com/askpage.html
http://www.colonialsupply.com/resources/radiator.htm
http://www.hydronicalternatives.com
http://www.runtal.com

Re: Old, cast iron radiators vs Slant Fin radiators

When I reno'ed my home (1922 old) I ripped out the forced hot air and installed Burham Radiant cast iron throughout divided into four zones. It was a little costly with all the feeds/returns/cast iron rads/ etc. but the best money I spent besides all the new installation in the house. You can have it cruise at low temp or crank the boiler to get them cooking at 200°

1917house
Re: Old, cast iron radiators vs Slant Fin radiators
LIHR wrote:

When I reno'ed my home (1922 old) I ripped out the forced hot air and installed Burham Radiant cast iron throughout divided into four zones. It was a little costly with all the feeds/returns/cast iron rads/ etc. but the best money I spent besides all the new installation in the house. You can have it cruise at low temp or crank the boiler to get them cooking at 200°

Hi, can I ask how much you paid? Right now I have 3/4" copper piping linked all around my basement ceiling. I used to have electric baseboard heat and I wanted hot water radiant. Slant Fin baseboard radiators were put in but they're not keeping my house warm. I need to have more installed but then I got the crazy idea to put in the old cast iron radiators. As it stands I just have one loop that would connect all the radiators. I've had people tell me it can be done this way and I've had people tell me it has to be closed loops like you have. It's been frustrating. I'm meeting with a technician today and he's going to look at my radiators. Up to this point I've spent about 14,000 to have the pipes and Slant Fins installed and that also includes the 6 old radiators I just bought. Spendy is correct.
Jay

Re: Old, cast iron radiators vs Slant Fin radiators

Whoa. Slow down. First off, the problem is that you are spending money on stuff before you even know what you need to buy. If you have the slant fin installed already, you will save the most money by correcting the mistakes of installation.

You absolutely need to do a heat loss on your home so you know how much baseboard you need. You also need the information to make sure your piping is sized correctly. There is also a limit to how much baseboard you can have on one loop. If the baseboard is 3/4", I believe the limit is about 60'. If the baseboard is run in series, then the rooms at the end of the run will have cooler water and need more baseboard than the rooms at the beginning of the run.

You should not mix copper fin tube baseboard with cast iron radiators. Cast iron heats up slowly and dissipates heat slowly. Baseboard heats up quickly and dissipates heat quickly. So you will have uneven heating if you mix them.

Check out comfort-calc.net. Lots of good info in the tech menu.

Do your heat loss!

brewster
Re: Old, cast iron radiators vs Slant Fin radiators
drooplug wrote:

Whoa. Slow down. First off, the problem is that you are spending money on stuff before you even know what you need to buy. If you have the slant fin installed already, you will save the most money by correcting the mistakes of installation.

You absolutely need to do a heat loss on your home so you know how much baseboard you need. You also need the information to make sure your piping is sized correctly. There is also a limit to how much baseboard you can have on one loop. If the baseboard is 3/4", I believe the limit is about 60'. If the baseboard is run in series, then the rooms at the end of the run will have cooler water and need more baseboard than the rooms at the beginning of the run.

You should not mix copper fin tube baseboard with cast iron radiators. Cast iron heats up slowly and dissipates heat slowly. Baseboard heats up quickly and dissipates heat quickly. So you will have uneven heating if you mix them.

Check out comfort-calc.net. Lots of good info in the tech menu.

Do your heat loss!

It's an old wive's tale that says one can't mix cast iron rads with baseboard---we've done numerous installs over the years without any problems and a good heat response---we do prefer two-pipe and venturi piping arrangements as opposed to series piping.

1917house
Re: Old, cast iron radiators vs Slant Fin radiators
drooplug wrote:

Whoa. Slow down. First off, the problem is that you are spending money on stuff before you even know what you need to buy. If you have the slant fin installed already, you will save the most money by correcting the mistakes of installation.

You absolutely need to do a heat loss on your home so you know how much baseboard you need. You also need the information to make sure your piping is sized correctly. There is also a limit to how much baseboard you can have on one loop. If the baseboard is 3/4", I believe the limit is about 60'. If the baseboard is run in series, then the rooms at the end of the run will have cooler water and need more baseboard than the rooms at the beginning of the run.

You should not mix copper fin tube baseboard with cast iron radiators. Cast iron heats up slowly and dissipates heat slowly. Baseboard heats up quickly and dissipates heat quickly. So you will have uneven heating if you mix them.

Check out comfort-calc.net. Lots of good info in the tech menu.

Do your heat loss!

Hey I guess I now know that everything I put on this board will show up. First of all, I didn't mean to broadcast how much money I spent. Now that it's out there - most of that went into infrastructure. I didn't have any piping in my house - all that needed to be put in. The 3 Slant Fins were the cheapest part of what was done so I'm decided to upgrade before I put any more in. The biggest problem with this project is finding good, reliable information. It seems that everyone has a different opinion of how this is supposed to work. The plumber who installed the pipes did a bang up job. He just didn't know much about heat. I know that now. I have another guy who's going to finish this project up. I think, after days and days of research, we all have a fairly good idea of what to do next. I'll keep you posted.

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