Replacing Steam Boiler

kframe

George,

Glad you've found your way over.

There are some real steam heads here, so you should be able to get all the answers you need, and more.

I'll toss in with a few more answers...

Cast iron is still the material of choice for residential steam systems.

New systems do tend to use less water, yes. I don't know about causing problems when placed in old systems, though. As long as the new systems runs on the same amount of steam pressure (typically no more an 1 to 2 lbs per sq. inch) and is properly sized to the area you're heating, it should be a problem.

My parents replaced an 1897ish coal converted to oil boiler in the early 1980s, using a new Weil-McLain high efficiency system. Worked like a charm, no problems at all, and the fuel expense was a lot less.

Most oil systems max out at around 85%, and steam systems are by their very nature a little less efficient, so that's actually about as high as you're going to get.

I'd say size for your expansion now.

As for converting to hot water, it can be done, but it's normally expensive, time consuming, and has its own set of problems.

Chances are, for the minimal amount of efficiency you'll gain you'll NEVER recoup the cost of conversion.

I'd say learn to love your steam system.

George Fisher

Steam Boiler Replacement

I'm finally rebounding after a few years of unemployment and can now replace my residential steam boiler. Because of financial situation I want to do as much as I can myself as long as it's legal and safe. The system I have is an old (between 50 and 100 years old), one pipe, cast iron steam heat/hot water system. Over the years the hot water tank was removed and the burner upgraded to gas. Except for a leaking tank, the overall system still works great with absolutely no problems. But, after doing some research I have some questions I'd like some advice on before I proceed.

First, Is there a boiler material (i.e. steel, ?) that is preferred over the cast iron and why?

2d. I've read that new boilers use less water and have some other improvements that might cause problems when placed in an older system. Are these really a concern and what should I do to prevent problems? By the way, I'm sure slope is not a problem.

3d. What is a good efficiency rating for steam boilers? Most I've seen are around 81 to 82%.

4th. I currently heat one story of about 1000 sq ft. Within the next 5 years I plan to expand either up or out to have about 1500 heated square feet. Should I size the new boiler to existing and add a second heating system later or size for the 1500 now?

5th. Aside from the benefits of steam heat, would it be worth considering a change to forced hot water to take advantage of increased efficiencies, side wall venting, etc.?

6th. Any other comments?

Thanks for any help/input!!

Unknown

I agree

All good stuff. I'd add that if you are going to add size to the boiler for the new addition, do the piping and radiator plan for it before you select a size.

Are you going to zone it? How? Is the header and main piping the right size, and is it in the way of the new main for the added radiation?

Will a boiler that big have water level problems with the original zone because it is overfired? I hate that, when it happens. You make steam faster than the mains can take it and the water starts pushing on the returns, and flying down out of the boiler and gauge glass. The cure is to fire it at the correct rate for the load. Hopefully, that is within the boiler's firing range.

How you size the radiators in the new part is important. If it is on the same zone as the rest of the house, you can't really expect balance in the whole house if you put little radiators in the new part, and there are huge radiators in the old part.

I'd consider the options in piping, before I chose the boiler. You need to do all of this math eventually, this is the right time to do it.

Noel

Steamhead

KFrame is right, you've come to the right place

and I'll try to answer your questions as you asked:

1. I'd pick cast-iron every time. It is much more durable than steel on steam systems. I can't remember the last time I saw a residential steel steam boiler being marketed- they're almost all cast-iron now.

2. In most cases the new boiler will have enough water in it to fill the system with steam, assuming the pressure is kept low. Two things to remember here: 1- when you take a certain quantity of water and boil it into steam, it expands 1700 times; and 2- steam is a gas, so if you compress it by building pressure it will take up much less space, which you then have to make up for by generating more steam! See my comments on venting under #6 below.

3. Most steam boilers have AFUE ratings from 81-85%. For the most part these are not nearly as complicated as higher-efficiency boilers, which means they are easier to service.

4. Do a heat-loss calculation on the proposed addition, and size the new boiler to include this amount. You can down-fire it temporarily while it is serving only the existing house.

5. I wouldn't convert to hot water. There are many pitfalls to this and as KFrame says, you may not reap any benefits. Sure, some hot-water boilers have very high AFUE ratings, but they are much more complicated than the usual steam boiler and parts may not be readily available if needed. I know you wouldn't want to encounter this on a 5-degree night!

6. The system must be as efficient as the boiler for good results. Air venting is crucial. Steam mains must have vents that will let all the air out of them in a minute. Radiators must have properly-sized vents too. And all steam pipes must be insulated.

Where are you located? I'm sure you can find someone near you on the Find a Contractor page of this site.

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Unknown

Brings up a question

I know that some new oil steam boilers can be downfired for just this situation - Peerless ECT and Burnham V8 series are 2 brands . But which brands of gas boilers can be downfired , according to their own literature ? Its been quite a while since I installed a gas steamer .

Unknown

not many

on atmospheric burners, too much excess air goes up through the boiler if you downfire them.

Gas power burners in wet base boilers can be downfired. Only to a certain point, though.

Noel

Bob_19

Boiler

Steel is stronger than cast when comparing stresses applied, but for a residential unit cast is suitable.

1lb of water will produce 1 lb of steam, and a newer unit will be sized with that very simple principle in mind. With any boiler you are producing lbs of steam an hour. Newer units though will produce that steam at a cheaper cost (hopefully). What to keep in mind here is that you will need so many btu's to offset heat loss in the structure your heating, and that will be plugged into a sizing survey. Usually older boilers were sized for that and then some, older houses had greater heat loss.

Efficiency at those numbers are normal. One of the reasons it seems low is that when calculating efficiency feedwater temp needs to be taken into account. Usually it's low for residential boilers. Industrial boilers run in the upper 80's to 90's if run correctly, it's not easy, but possible.

Definitly size now like others have said, for any planned additions later, you'll be glad you did.
You already have most of what you need for steam, so you should consider staying with it.

Buy the books, they'll explain all this in greater detail.

Steamhead

and

if you have a digital tester such as a Bacharach or Testo, you can see when the excess air percentage starts rising- right there on the screen!

If you don't test, you don't know.

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