Sizing a steam boiler

gmcinnes

Very quick question. As I understand it the correct way to size a steam boiler is to measure the EDR, convert it to BTU/hr and move on with your life.

There's no need to calculate heat loads or other variables you can play with in a water system, right?

My motivation for asking is that my in-laws have a failing chimney flue, and would like to line it with a metal liner, but their current boiler flue pipe is 8", and an 8" liner is too large to go around a bend in the chimney flue.

As in so many cases though, their current boiler might be oversized, and I'd like to rule out fixing it by changing the boiler before they have to start taking the chimney apart to rebuild it.

KC_Jones

Actually it's even simpler than that. You add up the EDR and go right to the boiler specs, they list the sq ft rating for the boiler right there. So you get your EDR, then find the closest boiler without going under. Well not much under anyway. IF I had 322-330 and a boiler rated for 321, I'd do that boiler I would not go bigger.

gmcinnes

Perfect. Thanks KC. That's exactly what I thought. Much simpler to figure out, but so much less fun to nerd out on

leonz

If you have enough ceiling height in the basement:

Be sure to plumb in a drop header or double drop header into your thinking about this as it will help make dry steam for heating the radiators much faster and should keep them hotter longer.

ChrisJ

leonz said:

If you have enough ceiling height in the basement:

Be sure to plumb in a drop header or double drop header into your thinking about this as it will help make dry steam for heating the radiators much faster and should keep them hotter longer.

No,
Please do not do a double header of any kind.

leonz

OK, asking as a lay person what is wrong with a double drop header??
Is it because it is a single family home??

A drop header to make dry steam will only provide many dividends to the home owner.

ChrisJ

leonz said:

OK, asking as a lay person what is wrong with a double drop header??
Is it because it is a single family home??

A drop header to make dry steam will only provide many dividends to the home owner.

A normal drop header may or may not provide drier steam than a standard header.
A proper header of any kind sized correctly in theory should provide dry steam.

Doing a double header is a complete waste of time and money and the only time you see it is when someone tries to re-use old piping instead of just cutting it out.

Unless you mean using two risers into a header, and even that highly depends on the boiler and the size of the boiler. On most residential boilers a single 3" riser is plenty.

gmcinnes

FTR, if it matters, this is a Brooklyn brownstone (think Sesame Street), not a single family home. Like most of them, it's split by floors into apartments.

There's one boiler, with one thermostat on the first floor. Not ideal for the other tenants, but it is what it is. In the grand tradition of NYC they keep the thermostat too hot, and the tenants deal with it by opening windows . It's 1918 pandemic approved!

They may not have been getting good dry steam previously, because the condensate return pipe, which is under tile in the basement rotted out. Then again, the system is probably more than 100 years old. Anyway, that's off topic.

leonz

ChrisJ said:

leonz said:

OK, asking as a lay person what is wrong with a double drop header??
Is it because it is a single family home??

A drop header to make dry steam will only provide many dividends to the home owner.

A normal drop header may or may not provide drier steam than a standard header.
A proper header of any kind sized correctly in theory should provide dry steam.

Doing a double header is a complete waste of time and money and the only time you see it is when someone tries to re-use old piping instead of just cutting it out.

Unless you mean using two risers into a header, and even that highly depends on the boiler and the size of the boiler. On most residential boilers a single 3" riser is plenty.

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If I remember Dans writing correctly he said that the more tapping's you have in the steam chest the faster you can deliver steam.

Plumbing in 2 risers into a larger header pipe with the condensate drain back to the boiler to create the drop header was what I was referring to.

Plumbing a 3" riser into a 4" drop header would work well too.

ethicalpaul

You don’t even need a single drop header if you pipe it as directed in the manual. Peerless for example doesn’t even put drop headers as an option in their manuals. 

But they don’t hurt if done right and they can make it easier to fit the pipes.

https://youtu.be/4IymyZB4wlI