Boiler size advice for confused homeowner

SquareRuth

I am a homeowner who must buy a new boiler for my one-pipe steam system.



I am confused about the correct boiler size to insist on.



I measured my square feet of steam, and it comes to only 112 sq. ft.  I read in Dan's book _We Got Steam Heat,_ that removed radiation will increase the number you use in order to compare to the boiler ratings, as they are figured on a conversion factor of 1.33, but you might want to use a larger factor, based on your piping.  There have been at least two radiators removed from the first floor, and perhaps others from the second floor (can't tell re: second floor).



In any case, even if you use a conversion factor of 2.0 (!? -- just for example, don't really know why I would choose 2.0 vs any other theoretical factor), you only get up to 168 sq ft rating for the house (112*2.0/1.33).  (It is true we may want to add additional radiation later; perhaps replace one of the removed radiators [+about 24sf], and/or increase the size of one or two of the existing radiators [+about 4sf/added section].)



I've been quoted several different sized boilers, all evidently the smallest available to each contractor:

- 196 sq ft Weil-McClain

- 196 sq ft Lennox

- 217 sq ft Smith

- 233 sq ft Peerless

- 281 sq ft Utica



I am not considering the Utica.  But considering my system as above, how much difference would it make to my system if I went with the 217sf instead of the 196sf?  How much difference if I went with the 233sf?  (There are reasons besides boiler size to consider these two contractors.)  Dan's book says if your boiler is too big, it will cycle more, which will make it less efficient and wear out the controls faster.  Are we talking "slightly less than ideal" efficiency, or "really inefficient" at these sizes?  Are we talking about wearing out in "50 years rather than 70 years," or wearing out in "10 years rather than 70 years," at these sizes?



I know it is impossible to answer these questions with a lot of certainty, especially if you haven't see the system.  But does any knowledgeable pro out there have a ballpark kind of opinion?



It seems like there is some difficulty for contractors to provide a boiler from a supplier they don't usually do business with, although it may be possible.  But also I am wary of asking a contractor to install a boiler he is not familiar with -- I'm not sure if this is actually an issue or not.



Many thanks for any insights!

Dave in QCA

Are you sure???

Before answering any of your questions, let's double check your figures for radation.  By the way, it is the EDR of the radiaton that you are measuring.  It is measured in sq ft of surface are.  Boilers are sized to match, and they already have the 1.34 piping and pickup factor figured in.  You can't measure the steam.



Your figures seem very low for your EDR.  4 or 5 small radiators would normally have a greater EDR than what you are indicating.  Can you take a picture of your radiators?  Are they column type, large tube, or small tube.  How many columns, or tubes are in section?  How many sections?  How tall?

Brad White

I agree with Dave

that sounds like a very small house or an EDR mis-measurement.

A general description of the radiators or photos at oblique angles so we can see the section ends/tubes and gauge the height will help to confirm.

Dave in QCA

examples

These radiators happen to be on a hot water system, but they are measured the same way.

The first example is a column type radiator.  It has 3 columns in each section and is 38" tall.  We know that a radiator like this has 5 sq ft /section.  There are 10 sections, so it would be 50 sq ft EDR.



The second example is a large tube type radiator.  It has 5 tubes per section and is 38" tall.  We know that this type of radiator also has 5 sq ft/section.  There are 6 sections, so the EDR is 30 sq ft.

SquareRuth

Radiator pics and dimensions

Thanks so much for your attention!  We have five radiators, pictures attached.  I measured their EDR based on a document another poster offered on this Web site:  Replacement Boiler Sizing Chart (also attached).  Using these instructions, I figured my radiators were all column type.  Although the dimensions do not _exactly_ match the choices in the chart, I rounded to place them all in the chart at 7-3/8" wide (2 columns), and either 38" or 32" tall.  The actual widths and heighths are:

1.  7-1/2" wide, 37-7/8" high, 6 columns

2.  6-3/4" wide, 31" high, 6 columns

3.  6-3/8" wide, 37" high, 5 columns

4.  7-3/4" wide, 37-5/8" high, 6 columns

5.  6-3/4" wide, 37" high, 6 columns

Numbers 1 through 4 are on the first floor, and #5 is on the second floor, above #2.



(I've tried to load the pics so they will show in the same order, but they may come out backwards.  The one with the pan of water on it is #5.)



Thanks!

Mark N

Don't buy more boiler than you need

Do you use oil or gas? If it is gas check out the Burnham IN-3. Its net EDR is 158sqft of steam. You have a very small system, don't get a boiler that is twice as big as you need.

Dave in QCA

You EDRs are

I refigured you rads and came up with 113 sq ft EDR.  It looks like you have several that are 24 sq ft.  If you allow for replacing the ones that are missing, you can just add them in.  So that would still give you a total edr of 137 or 161 sq ft.



Is your steam main in the basement insulated?  If not, the piping and pickup factor needs to be higher, say 1.5.  Burnham Independence is rated for 158 sq ft.  But, if you need to use a factor of 1.5 instead of 1.34, because for example, you main not being insulated, you would calculate as follows.  

Assume you might add 2 rads, so you want to be able to heat them.  The total EDR would be 161.  But, if you want to use a 1.5 factor instead of 1.34,  you would take your 161 / 1.34 x 1.5 = 180 EDR   (this would be the boiler rating you would need to be able to heat 2 added radiators, and if you were accounting for unusual piping and pickup factors, such no insulation on your mains in your basement.



By the way, what is the size of your current boiler?  What is its actual firing rate?

Charlie from wmass

Thats pretty close to the right size she is quoting

It is a small system. I think some people measured and others are just going from the old boiler size. The current boiler is oil fired and down fired a lot. The weil is as small as they come.

SquareRuth

Pipe insulation; current boiler size

I am a little confused about which pipes are supposed to be insulated; I suppose all of it?  What we have is no insulation on what I gather is called "near-boiler" piping (all pipe names are gleaned from Dan's book and online, so I hope I'm saying it correctly):  boiler riser, header, system riser, about the first 16 inches of the steam main, equalizer, and some of the drip connection .  The rest of the main is all insulated with that asbestos-containing material, subsequently wrapped in plastic.  Except that we do have these dry return lines which hang below the steam mains (two), doubling back from part-way down the steam mains back to drip connections.  They are copper until they get to the main vents at the drip connections  We are getting them replaced with steel in the upcoming boiler replacement.  These were not insulated until we blithely put that Home Depot-acquired plasticky foam-style pipe insulation on them a few years ago, so now they have that.  In any case, when these are replaced, we would insulate them properly, too.



I understand that one issue you did not bring up is missing radiation, which would also increase the factor from 1.33 to a higher factor.  See my original post for information about missing radiation.



I do not know the size or firing rate of my current boiler; the plate identifying it is completely rubbed out.  But from what I've read in Dan's book, I bet it's too big and we wouldn't want to base our new boiler on it!  The current boiler is oil-fired; we are going to gas-fired.

SquareRuth

How contractors picked boilers

Thanks for posting!

Everyone (except one "knucklehead") measured, but only one contractor (!) went outside the "box" of their usual supplier to find a smaller boiler than the smallest offered by their usual supplier.

BobC

The right contractor is most important

Always consider that the quality of your installer trumps the choice of boiler. A well installed boiler will be efficient, quiet, and long lasting.



Bob

Brad White

My goodness

that is a small system!

If you are in that range of 112-113 SF EDR, your heat output net to the space is only 27,120 BTUH.



It sounds cozy!



Ruth, you are in good hands here and that contractor who went looking for a smaller boiler gets points.

SquareRuth

Old and new: boiler size & drip returns(?)

Anyone have an opinion on my question?

Q:  If a boiler rated for 196 sq ft EDR is the best choice, what difference specifically would be experienced with a boiler of 217 sq ft EDR or 233 sq ft EDR?

I understand the concept of right sizing.  Does anyone have any experience with real-world consequences of the differences?  I'm gathering that, while it wouldn't be perfect, it doesn't really matter _that much_?



A new question:

A contractor today told me that he would combine my two separate drip returns (I think this is what these pipes are called)  into one when replacing these copper pipes with steel.  I have a hunch that might not be a good idea.  Any input?



Thanks!