steam boiler sizing

Boilerpro_5

On many vapor systems the 80% rule applies. The radiators are designed to heat only 80%. In addition, if there are enclosures etc on the rads this also reduces radiation capacity. On high end homes, I strongly suspect the system was designed for these enclosures to be used. Radiation capacity drops again, usually about 15%. These two together will give you only about 70% output of the installed radiation, so only 70% of the full size boiler is needed. If the radiation is way too large, installing orifice plates in the supply valves would allow you to effectively downsize the capacity, allowing a lower capacity boiler to be installed and improving boiler efficiency. Give Tunstall a call, they have information about this and can supply the orifices. Also, on a system so large, modular step fired steamers would seem like a logical choice, so you can get much improved part load efficiency. I have installed a couple of Slantfin modulars and they work very well. Another option would be to use a modulating burner on a larger boiler, preferably a 3 pass wetback boiler. This could very possibly give you constant flame on conditions on typical winter days depending on how the system is controlled. I have a couple modulating burner steamers and they run about 83% or better efficiencies when tested on low fire. Both of these boilers had previously been on/off units with typical problems of running too high pressure, poor control, and poor burner set up. Now with getting the basics right and modulating burner operation, there have been significant fuel usage reductions.....40% on one and the other still needs to be calculated.

Boilerpro

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Dan C.

big residentail boiler

I am sizing a boiler for a house that has a two pipe steam system. I measured all of the radiators and it comes out to a Burnham V905A. I have never had to use a boiler this big in a house. It is a very big house with very big radiators. Does this sound right? I have attached a picture of one of the radiators that I did not count and also a picture of the devices that are on the radiator returns. Also I did not include a 3 sec sunrad from one of the bathrooms. I used the edr ratings out of the burnham heating helper

38" high 3 columns 20 sections,
38" 2 col 8,
26" 6 tube 20,
28 2 col 17,
45 3 col 12,
18 5 col 20,
45 4 col 10,
38 2 col 7,
38 2 col 7,
38 3 col 16,
38 3 col 20,
38 3 col 7,
38 3 col 16,
20 5 col 9,
38 3 col 10,
cieling type radiator 3" thick 13 1/2" tall 22 sections,
38" 4 tube 7,
38 3 col 13,
38 3 col 13,
38 3 col 19,
38 3 col 8,
38 3 col 18,
38 3 col 18,







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Steamhead (in transit)

That's an \"O-E\" Vapor system

and yes, that system is big. This must be a mansion!

The "steam trap" is actually a water seal/check valve unit. It is described on page 264 of "The Lost Art of Steam Heating". The system should be set to run at no more than 8 ounces pressure.

If any rads have trouble heating, you can clear the vent hole in the return elbow. I believe this hole is located in the middle of the screw behind the check ball.

If there are no vents on the steam mains, you will need to add them. Measure the length and diameter of each main and we can tell you what's needed.

The dry returns should have main vents on tall risers. If these are the originals, they should be replaced with non-vacuum vents.

The radiator in the pic is a "pantry radiator" or "plate-warming radiator". That one would have a rating of 23 square feet, asuming it had a length of 23 inches and a width of 13 inches.

On the Sunrad, if the sections are 20 inches high and 5 inches deep, each section is 2.15 square feet. If the sections are 23 inches high and 7.5 inches deep, each section is 3.4 square feet.

On the "ceiling type radiator 3" thick 13 1/2" tall 22 sections", it depends on whether the sections are 13-1/2 x 21 (7 square feet per section) or 13-1/2 x 29 (9 square feet per section).

On your other rads:

38" high 3 columns 20 sections= 100 sq ft,

38" 2 col 8= 32,

26" 6 tube 20= 80,

28 2 col 17= 45.3,

45 3 col 12= 72,

18 5 col 20= 95,

45 4 col 10= 100,

38 2 col 7= 28,

38 2 col 7= 28,

38 3 col 16= 80,

38 3 col 20= 100,

38 3 col 7= 35,

38 3 col 16= 80,

20 5 col 9= 49.5,

38 3 col 10= 50,

38" 4 tube 7= 29.75,

38 3 col 13= 80,

38 3 col 13= 65,

38 3 col 19= 95,

38 3 col 8= 40,

38 3 col 18= 90,

38 3 col 18= 90.

1464.55 square feet so far.

The V-905A is rated 2021 square feet. The V-904 is rated 1504 square feet, and would probably be a better match for this system unless those last two rads put you way over the line. On Vapor systems we've found that it's OK to use a boiler whose rating is "just enough" to fill the radiation, since the steam is in such an expanded state from running at ounce pressures. You may also find that the Weil-McLain 5-80 (1608 square feet) or 6-80 (1983 square feet), or another brand of boiler with a closer rating to your final radiation count, is a better match for this system.


How about some boiler room pics?

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Dan C.

sorry

No boiler room pics. But there are no vents and someone already added a condensate receiver. the boiler is about 20- 30 years old. The header is incorrectly piped but the guy says it works fine. So I was going to re-pipe the header and leave the tank and all of the return piping the way it is. When I go back I will take pictures of the boiler room. I did my math wrong. I had 1665 which is why I saying v905 I would rather use a Burnham boiler. Do you think that would be a bad idea because of the fact that the rating is lower than what I need? I also missed one radiator so I will be over 1504 but not by much.

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Steamhead (in transit)

Condensate receiver isn't needed

go back to simple, uncomplicated gravity return and venting. It'll work fine.

As far as the boiler goes, get the true EDR for the Sunrad and the ceiling rad and see where you are. If it's just a few square feet over the V-904's rating it shouldn't matter as long as the steam pipes are well insulated. If it's more than that, try to match it without going too far over.

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Boilerpro_5

A couple other thoughts on sizing

The 80% rule may apply here, vapor systems often are only supposed to heat the radiators 80%. Also, if those radiators are installed in decorative cabinets or enclosures the output is cut ounce again. The amount varies by cabinet type often times about 85% of full output. These two items alone will reduce radition capcity to about 70% of installed. If indeed the radiation is way oversized, you may want to install orifice plates to limit output. In turn, you can reduce the boiler size to match you new load. Give Tunstall a call about this, they have the plates and sizing information. You could end up with a much less expensive boiler installation that would help cover the costs of the time spent calculating room by room heat loss and installing the orifice plates. And, the customer would get a top notch system running at peak efficiency. You may want to use staged modular steamers to pick up efficiency and cut install time. Here's one of mine and Gerry Gill and Steve and company have stepped forward from this in a very recent install posted here.

Boilerpro

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Dan C.

thanks

Thanks for the quick responses steamhead and boilerpro. I will take pictures if I get the job.

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