Sizing hot water boiler

KevinNY

I have a gas fired hot water boiler that we're replacing. It was originally an oil boiler, so it's about 75 years old, and was converted by someone before we bought the house.



I'm trying to understand sizing. I had a friend of a friend use some software with measurements I gave him to calculate our heat loss. It was roughly 77,000 Btu/hr. He also took the measurements of our cast iron baseboards / radiators and calculated a heating capacity (not sure if that's the right term) of 101,000 Btu.



My question is twofold. Do I need to choose a boiler that meets or exceeds the heating capacity? Or is a boiler that exceeds the heat loss (say an 80,000 Btu/hr) all I need?



Also, when looking at the spec sheets from contractors I see three Btu ratings - Input, DOE and IBR. Which one should I use to choose the right size?



Thanks,

Kevin

James Day_2

boiler

You want to size the boiler based on your heat loss, not on installed radiation.  If your heat loss is 77,000 try to install as close to that as you can get.  I size based on d.o.e. , but everyone has there own way of doing so.

KevinNY

DOE / IBR

OK thanks James.



I figured I shouldn't be using the Input BTU because depending on efficiency some of that is going right up the chimney.



But what is d.o.e.? What is I.B.R.? And why would someone use one number and someone else use the other?

James Day_2

doe

IBR allows for a 15% loss through all of your heating pipes.   where in NY are you located

Alan (California Radiant) Forbes

DOE and IBR

The DOE (Department of Energy) heating capacity presumes that the heat lost from the boiler jacket and distribution piping will be used to heat the building.  Use this rating if your boiler and distribution piping are within the heated space.



The I=B=R heating capacity presumes that your boiler and distribution piping are not within your heated space and will be lost.

KevinNY

doe / ibr

I'm at the west end of the state, northeast of Buffalo by 15 minutes.



In my case, the boiler is in the basement. I have two steel radiators down there, so it's partially heated. All the piping runs under the floor joists of the main floor, and then up into the walls where each baseboard/radiator is.



So I guess a lot of the piping length, if it's losing heat, is losing it to the underside of the first floor. And then of course some of it is being lost in the uninsulated walls. Is that correct?



Almost sounds like I need to use something between DOE and IBR... Am I on the right track?

James Day_2

yes

either way you would be fine.   You will find that the boiler you will choose will meet your requirements with both doe and ibr.  

icesailor

IBR Ratings:

That's not how I always understood the IBR Ratings,

That when you do an absolute soup to nuts design, with lengths of runs, friction loss through ells and fittings, every possible thing to get you to your total heat loss, which includes a number for "Piping and Pick-up", that is what a boiler will need to provide. Under the IBR method, an amount equal to 15% is deducted from the boiler output rating to cover this loss so you don't need to add it to the heat loss load. The exception that IBR gives is if you have any "unusual" piping or situation.

What is given, as far as I am concerned is that if you do an accurate heat loss, and you come up with some number, and the number is below the IBR number, you will be good to go. If the number was above the IBR number but below the DOE or ASHRA rating, you are  on your own.

Whatever works for someone. I've always used IBR. IBR heat loss, IBR piping, IBR radiation ratings and IBR boiler ratings. I've never been sorry.

icesailor

IBR Ratings:

That's not how I always understood the IBR Ratings,

That when you do an absolute soup to nuts design, with lengths of runs, friction loss through ells and fittings, every possible thing to get you to your total heat loss, which includes a number for "Piping and Pick-up", that is what a boiler will need to provide. Under the IBR method, an amount equal to 15% is deducted from the boiler output rating to cover this loss so you don't need to add it to the heat loss load. The exception that IBR gives is if you have any "unusual" piping or situation.

What is given, as far as I am concerned is that if you do an accurate heat loss, and you come up with some number, and the number is below the IBR number, you will be good to go. If the number was above the IBR number but below the DOE or ASHRA rating, you are  on your own.

Whatever works for someone. I've always used IBR. IBR heat loss, IBR piping, IBR radiation ratings and IBR boiler ratings. I've never been sorry.

bob eck

new boiler?

look at the triangle tube prestige solo and their prestige excellence 95% AFUE condensing gas boilers.

for your hose I wold look at using their PS110 boiler only need to add smart 40 or larger stainless steel indirect water heater for domestic hot water or their PE110 boiler with built in SS indirect water heater that will deliver 180 GPH for domestic showers ect...

both boilers come with outdoor reset so the boiler will only deliver the right water temp to your baseboard and radiators depending on outside temp.

Great boiler vents with PVC pipe no chimney needed. can get 5 or 10 year parts and labor warranty to keep you repair cost under control. normal maintenance not covered by the extended warranty. check them out at www.triangletube.com

Alan (California Radiant) Forbes

DOE vs. I=B=R

I paraphrased Siggy from his book, Modern Hydronic Heating, pages 56 and 57:



http://books.google.com/books?id=WdPg_1aTtr8C&pg=PA56&lpg=PA56&dq=siegenthaler+doe+ibr&source=bl&ots=0bSiakjkVF&sig=ue4Y58mgAp2SDSQk--zgyskVjTk&hl=en&ei=TMJ2TZTSC43SsAO5v_XABA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBQQ6AEwAA#v=onepage&q&f=false



That's not to say that I ever use the DOE figure.  Like Mr. Icesailor, I've learned to always use the I=B=R capacity and it's never let me down.