Sizing steam boiler questions

Alden Maddry

I am looking to replace my old gas fired steam boiler and have a couple of questions on sizing the boiler.

1) Most of my radiators are standard column type so I can calculate their square feet of radiation but I have two radiators of a different type in my bathrooms. See attached pics. They are both fairly small. How can I calculate the square footage of radiation for these radiators?

2) Does the insulation of my house impact the sizing of the steam boiler in any way? I live in a 1931 brick Tudor house with no insulation in the walls - there are two layers of brick, a 3/4" air space and then the interior plaster walls. There is some rockwool insulation in the attic at the floor level (not between the rafters).

Thanks,

AM

JUGHNE

Think of the system of heating the radiators and pipes, not the heat loss of the house.
How far across did your existing radiators heat on cold days?
And was the existing radiation enough to heat the house?
Then are your steam pipes insulated?

ethicalpaul

From Dan's book, which everyone should buy: https://heatinghelp.com/store/detail/the-lost-art-of-steam-heating-revisited

it depends on the depth of the units. If they are 5", then it's 2.25 sq ft per section and if they are 7.5" deep, then it's 3.4 sq ft per section.

But I think that would depend on the insulation situation on the back, top and sides. If they are insulated, I would use the 2.25 per section number regardless I think.

I dislike these in-wall units if they are on an exterior wall because so much of their heat just goes to the outdoors, unless they are well-insulated (mine wasn't)

Jamie Hall

To reinforce @JUGHNE 's comment, with regard to your question 2: no, the insulation nor anything else about the house influences the sizing of a steam boiler. It is based entirely on the EDR of the connected radiation.

Alden Maddry

As far as I can see none of the steam lines in my system are insulated including the steam header pipes in the boiler room or the steam supply line in the cellar ceiling... would these uncovered lines be the equivalent of more radiators in terms of the radiation calculation? Because there are no radiators in my cellar I'm assuming the uncovered supply line provides some heat to this room which is an advantage... although the condensate return line is also uninsulated and this line also must provide heat to the room?

The two bathroom in wall radiators are built in to interior walls, not exterior walls.

ethicalpaul

What is your EDR count not counting the basement stuff? You should insulate those "mains", your system will operate better. Then if you need to add heat to the basement, you can. Is it finished? Or do you just spend a lot of time down there counting spiders or whatever

Historically, that would be covered by something called a "pickup factor" but I wouldn't worry about it.

Yes, the wet return adds some heat, but not nearly as much as steam does in its phase change from gas to liquid.

Since your in-wall radiators are on interior walls, I would use the smaller side of their EDR. This is because they will condense a lot less steam not being adjacent to the bitter winter cold.

Jamie Hall

Uninsulated steam mains provide remarkably little heat to the space in which they are located ( a 2 inch diameter main is, very roughly 120 BTUh per foot). What they do do is slow the delivery of steam to the radiators. There are other ways to heat the space, so insulate them.

Alden Maddry

Here (attached) are my radiation calculations so far (without including the 2 in wall bathroom radiators) and the tag from the boiler.

My cellar is finished so I'd like some heat to remain down in this space... but at this point there is plenty.

I realized after putting all of this together that I only have 12 radiators total in the house and 3 are not working well (or at all) and we have switched off 1 so 4 out of 12 radiators - 1/3 of the system isn't functioning...

I'm going to have a steam expert / plumber finally come in this year to check out and work on the system to get it back up to speed... probably should have done this a long time ago!

ted_p

I strongly encourage you to read this brilliant article in the System Help Center, by Dave Bunnell, @The Steam Whisperer :

Taking Another Look at Steam Boiler Sizing Methods

This one is worth reading. Thinking about for a few days. Then going back and reading again!

nicholas bonham-carter

Is the present boiler leaking, or otherwise problematic? How old is it, and does it use a lot of water?
I would work on making the system work properly, before changing the boiler.
Often this is as simple as replacing the main vents, and insulating pipe.—NBC

BobC

The vents on those radiators in the pictures are both Varivalve Heatimers. They vent very fast and can cause problems on steam systems. They don't have floats so they can spray water under unfavorable conditions.

Most steam systems benefit from low operating pressure, fast mains venting, and slow radiator venting.

Bob

ted_p

BobC said:

.......

Most steam systems benefit from low operating pressure, fast mains venting, and slow radiator venting.

Bob

Taking slow radiator venting to a whole 'nother level is the heart of @The Steam Whisperer's approach, when applied to 1-pipe systems.

nicholas bonham-carter said:

Is the present boiler leaking, or otherwise problematic? How old is it, and does it use a lot of water?
I would work on making the system work properly, before changing the boiler.
Often this is as simple as replacing the main vents, and insulating pipe.—NBC

What NBC said! Plus, if your existing boiler happens to be power-gas (a converted oil boiler, perhaps?), it can be down-fired by a good boiler man with a combustion analyzer, which opens the door to applying Dave's approach with your existing boiler as a sort of "whole system tune-up". If that works out, you might be so pleased with the results that you decide to keep the old Gal and run 'er till the wheels fall off.

While on the topic, when you do buy a new boiler, you should at least consider going power-gas, instead of atmospheric. Although more expensive, the advantages of higher combustion efficiency, dramatically reduced stand-by losses, and the ability to fine-tune your system by down-firing are very compelling.

Alden Maddry

My current Peerless boiler isn't leaking and doesn't use much water... I only have to add water every couple of weeks in the winter. The boiler is approx. 32 years old. I don't know if the current boiler is a converted oil boiler or not... although I do know that the previous owner converted from oil to gas, but not sure whether the boiler was changed as part of that.

I'd be happy to fix this system rather than replacing the boiler - insulating the pipes, replacing the vents and doing anything else that would help.

ted_p

What's the model # of your Boiler?

Is the burner a blower-like device hanging on the side of the boiler, something like this?



If so, it's power-gas.

If just it has multiple burner tubes underneath (like a typical gas fired hot water heater) then it's atmospheric.

Alden Maddry

The Model # is G-561-SW-I
and my boiler doesn't have the blower device on the side - the tubes are underneath so I guess that makes it an atmospheric.

ted_p

Yes, I'm sure it is.

I searched the Peerless website in hopes of finding docs for your boiler, to see what the specs are, but came up empty handed.

IIRC, @Hap_Hazzard has the same (or very similar) model Peerless, way over 30 years old, and it's still going strong; so don't be too quick to give up on what you've got! I bet he can to help out with tips and info about your boiler, and possibly even docs.

Hap_Hazzard

ted_p said:

IIRC, @Hap_Hazzard has the same (or very similar) model Peerless, way over 30 years old, and it's still going strong; so don't be too quick to give up on what you've got! I bet he can to help out with tips and info about your boiler, and possibly even docs.

Right you are. Mine is a G-561-W-S, which means it's a gas-fired, 5-section series 61 boiler for water or steam heating systems. Sometime back in the 80s they changed the model designation from 561 to 61-05 and made a few changes in the casting, then about 15 years ago they discontinued the series 61, but they are very similar to the series 63 boilers.

I'll attach a PDF of the IOM for the series 61 and 62, which isn't available from the Peerless website anymore. You may notice a few differences between the manual and your boiler. Most importantly, you won't find a skim tapping where it's shown in the tapping locations diagram, because the older ones didn't have them, so you have to improvise. Other than that I think you'll find the manual pretty useful. I still have my original manual, so I should be able to provide any info you might need when there's a discrepancy.

I'd encourage you to hold onto this boiler as long as you can. Flush out the sediment and do a blow-down every couple of years and clean the flueways in the fall before you fire it up and it should keep you warm for a few more years. The newer boilers might be more efficient, but they have thinner castings, so they won't give you as many years of service.

Kjmass1

Jamie Hall said:

To reinforce @JUGHNE 's comment, with regard to your question 2: no, the insulation nor anything else about the house influences the sizing of a steam boiler. It is based entirely on the EDR of the connected radiation.

Just curious, if you insulated your home, then right-sized all of the steam radiators with say radiators 1/4 the size to match the heat loss of the now improved home, and matched the boiler to your new EDR, would the new system cost significantly less to run vs keep existing radiator EDR and sizing to that?

ethicalpaul

No, not significantly I think. It would run more predictably, and be easier to balance, and it would cycle a lot less, but in the end, you make a btu by burning fuel at 80-something percent efficiency either way. A smaller boiler takes less fuel to get up to boiling of course, but against the cost of a new boiler, it would take several lifetimes to make that up.

And to add to the "power burner vs atmospheric" conversation, the power burners are very much louder than atmospheric boilers which can be noticeable in the living space depending on the house.

PMJ

Kjmass1 said:

Jamie Hall said:

To reinforce @JUGHNE 's comment, with regard to your question 2: no, the insulation nor anything else about the house influences the sizing of a steam boiler. It is based entirely on the EDR of the connected radiation.

"Just curious, if you insulated your home, then right-sized all of the steam radiators with say radiators 1/4 the size to match the heat loss of the now improved home, and matched the boiler to your new EDR, would the new system cost significantly less to run vs keep existing radiator EDR and sizing to that?"

The fuel bill is determined by the heat loss, not the size of the boiler or the installed EDR. To maintain temperature you have to replace what is lost. The capacity of the equipment installed doesn't change that. After insulating the same equipment has no choice but to run less and burn less fuel.

The answer to your question is no - primarily because radiator EDR downstream of what is needed doesn't affect anything. You actually need and do use less EDR on warmer days. Insulation has the same effect - as far as your system is concerned all the days are a little warmer than before.

I barely ever fill to 1/4 on my radiators on an average day. If they were all even bigger they would be even less full as a percentage but that would affect nothing.