Replacement Steam Boiler Advice Needed

Old 01-23-10, 02:23 PM
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Replacement Steam Boiler Advice Needed

We are going to replace a 1940's steam boiler (coal converted to oil fired) with a new unit.

There are some questions that we have for this install that I would like some experienced advice for.

Survey Data:
* Two pipe low pressure system with a float type condensate return pump.
* Total Square Foot EDR = 650
* Total calculated building heat loss = 160,000 BTU
* The building is single story and has about 125 feet of insulated 2 inch horizontal mains.
* The existing boiler has a water capacity of 8 gallons between the N.W.L. and the LWCO.
*The existing boiler firing rate is 2 GPH
* On a cold start the existing boiler runs for 12 Minutes (starting from the time the header gets hot) and steams off 4 gallons of water before the condensation pump will turn on to refill the boiler.

Question 1.
Due to the length of the mains what is a reasonable pick up factor to apply to this system....... is 1.5 sufficient? I calculate that with a pick up factor of 1.5 the replacement system should have a DOE Capacity of at least 234,000 BTU... Does this sound correct?

Question 2.
Of the currently manufactured boilers that I have researched, none have a water capacity that matches that of the existing boiler. I understand that I will need to install a "reserve tank" to supply the new steam boiler with enough water to produce enough steam to fill the radiators and the pipes of the system.

I calculate that I will need about 2.5 Gallons of "reserve water"...

What is typically used in these situations as a reserve tank? I have seen that some have used plain compression tanks, but a compression tank can be expensive, and I have not seen any horizontal CT tanks with both top and bottom fittings to connect to the system..... Does a pre-manufactured reserve tank exist?

Could I weld one from a length of 1/4 steel box beam and cover the ends with plates?..... Would that pass code??

IMPORTANT... Because the new boilers water capacity will be increased with "reserve water", Is it necessary to oversize the boiler to allow for that increased capacity, and if so by how much?

Question 3.
If I went with a tankless coil option on the new boiler, how much do I have to over size it to compensate for that heat loss?

Question 4.
I really like the "Peerless ECT" but it is expensive.
I have been told that the Crowns are good, and they are reasonably priced, but their largest residential boiler only has a DOE of 235.000BTU, and I don't think it will be big enough for this install.

Who else makes a good, reasonably priced boiler that is sized large enough to replace the existing boiler for this install?
Old 01-29-10, 05:56 PM
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Burnhams mega steam is the only steam boiler I will ever use. Period. I have never used a boiler that works as well and is as straightforward to install as the mega steam. I even bought their dropped header on the last one and it was slick. You really don't want the coil in any boiler like this. Use an indirect if you need domestic and cold start the boiler. It will kill you all summer long on fuel if you dont.

Old 01-29-10, 07:16 PM
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Maybe it time???

to get away from steam and start to think about going with a HW system. steam boilers don't typically last long anymore because the castings are much thinner than in yesteryear. It wouldn't be unusual to replace a steam boiler in 7-10 years..., but hot water warantys go out to 25 years... Steam is about 5,... I think, and requires watching the PH of the water closely...
Old 01-30-10, 08:49 AM
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As usual I play the devils advocate. I would keep the steam boiler as it can operate efficiently if properly installed and vented properly. They last a long time if maintained. The iron is as heavy as it always has been but with hotter flames and less water it is much more violent inside.
You need to verify the vents are good and no steam or water leaks for longevity.
You do not have to add a pick-up factor for the boiler it is already built in today. The manufacturer will deduct 33% for a pick-up which is good for residential insulated main installations.
Should not have to add a tank for water if the tank is at the end of the main or the main is a dry return. The only reason for adding a tank may be slow returns.
12 minutes for 4 gallons of water....I did not do the math but that sounds excessive. You may be surging or getting wet steam which both will put excess water in the mains.
See this link for more info.
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