Brand new game: Guess A Boiler Size!

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  #1  
Old 08-12-11, 09:46 PM
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Brand new game: Guess A Boiler Size!

Who wants to guess which size boiler I should buy? I have done the research on the internet about sizing guides, radiator tubes and square footage and I still really can't figure it out. I even read Dan Holohan's steam book that my neighbor loaned me. Well I read a few pages of it then I feel asleep.

My plumber needed all of three seconds to glance at some numbers on my old OIL boiler and say "yeah, a replacement gas would be $4000, installed." He's never been anywhere BUT the basement of my house so he couldn't possibly know if the sizing was right. My old oil burner is probably from the 60's.

Anyways here's the data:
Steam Heat. 100 year old house (balloon construction).
3 floor house (3rd floor is semi-finished attic)
1680sq/ft in floors one and two. Not counting attic.
4 radiators downstairs. 5 upstairs. two in the attic (long since disconnected and capped off.)
Not one piece of insulation anywhere in the house.
Newish double-paned windows (mostly)
Radiators are about 3 feet tall and 8 or 9 fins in the downstairs. 3 of the 5 upstairs are the same size, the other two are about 25% smaller.
Location: Western Mass.


The average of this forum's suggestions = my boiler size. Let the guessing begin!
 
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  #2  
Old 08-12-11, 10:11 PM
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Your plumber is probably correct as sizing of STEAM systems is rather critical and making the assumption that the original was sized correctly is actually acceptable in this case.

HOWEVER, I would strongly suggest that you do a major weatherization of your house BEFORE winter. Insulate and air seal that house and you will save a TON of money heating it. While you are doing that you should consider dumping that steam system for a modern hot water system.

I detest residential steam.
 
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Old 08-12-11, 10:29 PM
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I detest residential steam.
Not to get off subject but why? We had steam growing up and I thought it was the best heat. Well when it was on anyway. My father would wack us one if we touched the t stat. But I dont know if because we had no money or oil was expensive in the 70's.

Anyway to the OP. Follow Furds suggestion that the oringinal was probably sized correctly. The size of the boiler is directly related to the # of rads and size.

There will be guys that will give you the actual formula, but you will need to measure each section I believe and how many sections per rad.

I dont know steam that well. Only that it kept my arse warm as a kid on those cold North Jersey winters up in the hills.

"Tink, tink, tink" was the sound...LOL

Mike NJ
 
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Old 08-12-11, 10:56 PM
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These are numbers off the boiler (It's an "American Standard." I guess they don't only make toilets):
Gross output MBH: 186
NET IBR Water MBH: 161.7
Steam Sq. Ft: 581

My question is what is the Btu/hr input?
 
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Old 08-13-11, 12:30 AM
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BTU input is roughly 80% of the firing rate in gallons per hour multiplied by 142,000 or gph X 142,000 X 0.8 = BTU/hour input. The 80% is the average combustion efficiency and 142,000 is the average BTUs per gallon of #2 fuel oil. Your combustion efficiency may be a bit lower but should be better than 75% unless your boiler is in REALLY bad shape.


I spent most of my adult life working with steam (one way or another) in commercial and industrial applications. I love steam for many purposes and that does include institutional or large multi-tenant housing. BUT, steam does not play well in modern residences. It is expensive to zone steam heat and it often just can't be done for several reasons. Maintaining steam boilers is far more labor intensive than hot water boilers and few homeowners want to do what is necessary to maintain their boilers. In single-family residences steam is an all-or-nothing proposition and steam radiators do get hot enough to inflict serious burns. It is also a "point supply" of heat and unless very carefully designed, including furniture layout, it can leave parts of rooms uncomfortably hot while other parts of the same room will be uncomfortably cold. There are also more elements to go bad than almost any other form of central heating with the possible exception of heat pumps.
 
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Old 08-13-11, 10:14 AM
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There is no 'guess work' about it!

4 radiators downstairs. 5 upstairs. two in the attic (long since disconnected and capped off.)
Steam boilers are sized according to the installed radiation, not heat loss of the building.

The fact that two have been removed and capped may affect the sizing of the boiler.

There is much to be learned about steam heating systems here:

Technical Menu

This selection tells you how to calculate the square feet of your radiators.

Steam Information
 
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Old 08-13-11, 12:50 PM
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too complicated.

How about this:
120k Btu/hr?
Or should I go with a 230k btu/hr?

"BTU input is roughly 80% of the firing rate in gallons per hour multiplied by 142,000 or gph X 142,000 X 0.8 = BTU/hour input. The 80% is the average combustion efficiency and 142,000 is the average BTUs per gallon of #2 fuel oil. Your combustion efficiency may be a bit lower but should be better than 75% unless your boiler is in REALLY bad shape."

My GPH is 1.70 so according to Furd's estimate: 142,000 X 1.70 X .8 avg combustion eff = 193,120 btu/in

Should I get the 200k btu or the 230K btu knowing that there is only a small price difference between the two.

OR
should I go smaller? House has newish double paned windows and I will insulate the attic before the winter, so can I go 160k or even lower?
 
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Old 08-13-11, 01:33 PM
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Actually, with very little effort you can do what is necessary to reduce your boiler needs to below 100K. I know you're having fun, but in reality there isn't one person who has posted, original poster included, that would install a new boiler in an uninsulated balloon construction building with nothing but new windows and some future attic insulation.

What we need are the real numbers and those won't be available until the air sealing and insulation improvements are completed.

Bud
 
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Old 08-13-11, 05:04 PM
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Originally Posted by giambrone View Post
too complicated.
I wish I had your money.

Sizing the boiler IS extremely important if you want to have an efficient heating system. Insulating and weather-sealing the house, especially one of balloon construction, will pay for itself in less than two years, maybe even the first year.

The general rule is to NEVER install a larger boiler than the original and with anything other than steam heat it is often acceptable to install a boiler half the size (output) as the original or even smaller if aggressive weatherization has been performed.

Is your time really that valuable that you cannot take a couple of hours to properly measure your radiators and then compute the required boiler size? Figure how much more you will spend on fuel with an oversized and inefficient system and then tell me.
 
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Old 08-13-11, 06:32 PM
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Since you can't be bothered to take the time to measure up your radiators, then I'll help ya out some... I'll GUESS.

You need at least a 500,000 BTU boiler.

It's as good a guess as any!
 
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Old 08-13-11, 07:26 PM
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Nah, a 500k boiler is too small. He should use this one.


image courtesy firstechservices.com
 

Last edited by NJT; 08-14-11 at 08:57 AM.
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Old 08-13-11, 07:44 PM
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Who wants to guess which size boiler I should buy? I have done the research on the internet about sizing guides, radiator tubes and square footage and I still really can't figure it out. I even read Dan Holohan's steam book that my neighbor loaned me. Well I read a few pages of it then I feel asleep.

C'mon guys. He read the book and reserched it. Apparently he dont get it. Possibly one of you nice gentlemen can do the math for him.

Uhhh.... ohhhh..... Ok he has not even taken the time to measure the rads...... 'Never Mind".

Well he said it was a "game". Possibly he is just play'in with you all..........

Mike NJ
 
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Old 08-14-11, 08:55 AM
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Possibly he is just play'in with you all..........
That thought had crossed my mind.
 
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Old 08-14-11, 11:26 AM
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Tighten up the house all you want it will not change the boiler size. Will it help on your fuel bill? Yep, but may cause some short cycling. Converting to water will never payback the investment.
Verify all vents are working and there is a large enough main line vent. If two pipe steam are all traps working? Are all the steam lines in the basement insulated?

Steam FAQ
 
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Old 08-15-11, 08:50 AM
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If you want to accurately size the boiler, you need to know how much radiation is connected to it. If your current plumber didn't suggest that, he/she needs to be "fired" immediately. Find a real steam pro that will properly determine the corrected load, replace the radiator vents, replace/install main vents, check the pitch on all piping, insulate piping, etc etc. Near-boiler piping is critical, and what is currently installed may or may not be correct.

Steam systems get a bad rap because many heating tech's don't know anything about it. I suggest you use the "find a contractor" feature on the heatinghelp website, and find someone that lives and breathes steam: Find a Contractor

Lastly, you have been given some great advice to tighten up the house, especially since it is balloon construction.
 
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