Help calculating boiler size needed

RyanC

I have calculated the total square footage of my radiators to be 166.  Where I am starting to get confused is relating that to the ratings on the boiler.

The boiler reads at follows:

DOH MBH: 122/132

Steam Sq Ft: 381/415

Steam MBH: 91.5/99.5

Firing rate: 1.05/1.15

I am guessing firing rate is referring to the GPH of oil burned, but based on the tag from my last servicing there is a .85 nozzle on the burner.

Can someone help me figure this all out?



Thanks,

Ryan

ezzy travis

pick up load

166 is the total of radiation coming off the radiators? multiply that by 1.33 for your pick up load which factors in the piping from the boiler to the radiators

jpf321

before you multiply...

it's my understanding that the boilers already factor in 1.33 when they give their steam sq ft ratings .. however, you may want to find the original spec sheet to see if they have in the notes anything about adding in the 1.33 already...not simply from the boiler tag .. but the original spec sheet. you may also be able to figure this out by the BTUs .. in fact it looks like you can .. 122,000BTU / 240 = 508 / 1.33 = 382 which matches the steam rating they are giving you .. so they have already factored in the 1.33

RyanC

Boiler oversized?

So is my boiler way over sized then? 

Does the 166 sound small?  I know its hard to tell without seeing the rads.  It's a small house (1353sq ft) with 5 rads.

This was how I came up with the footage on the rads:

Kitchen: 4 tube, 23"H, 22 sections (4 tubes, but VERY narrow)

Dining room: 5 tubes, 23", 11 sections

Living room: 3 columns, 23", 13 sections

Hallway: 2 columns, 38", 8 sections

Bathroom: 2 tubes, 20", 8 sections (I guessed at this one.  It is very compact and recessed in the wall.  The vent is at the top and mounted on the front.  Maybe it is considered a wall radiator?)

The chart I was using based all the calculation on number of tubes or columns in each rad.

jpf321

it does seem so

your 166sf EDR sounds reasonable, whether it's exact or not i'm not sure, but it's a fair approximation. I have 14 rads of various sizes for a 3000sqft house and i have 384sq ft in EDR.



because your boiler is oversized by the tag info, may be the reason why someone installed a smaller nozzle (0.85) than the spec. i don't know anything about fire or burners so i cannot speak to that subject .. there are people here than understand fire very well. you may also want to ask over in the Oil forum.



what is the reason for your questions? are you looking to replace the boiler? are you having problems with your heating? do you want to be sure that you are burning efficiently? having that smaller nozzle on there may be the best you can do in terms of downfiring your burner since there are limits regarding how small a fire you can have. to do better, you may need to replace your boiler.

RyanC

Just trying to learn

I'm just trying to learn all I can about the system.  The heat works fine.  We really dont have any issues at all.  I need to insulate my pipes and add some main venting, but thats it really.  The boiler is over 20 years old; so it's effeciency is not great, but for now it is still working.

Nelson_4

More questions...

How many gallons of oil do you use per year? Does the boiler also supply hot water? Is the house drafty or well-insulated? What area do you live in?

RyanC

Answers

The boiler all supplies hot water through a coil.  The windows are all pretty tight, but the basement is drafty. The attic has a fair amount on insulation and the walls are not insulated. I don't know about oil as this is our first winter in the house.  I can tell you from 12/4 to 01/12 we used 165 gallons of oil.  We are located in Massachusetts.

Nelson_4

12/4 to 1/12 = 39 days

That works out to about 4.2 gallons per day. We have a similar sized house near Boston, and had our boiler replaced a couple of years ago with a Burnham MegaSteam. For a similar time period, we were using 3.9 gallons per day, so your usage doesn't seem too bad. Spring isn't too far off!

jpf321

what about per heating degree day?

you can't just calculate it based on calendar time...you need to figure out the HDD for the time period .. check out http://www.degreedays.net/ and calculate gallons/HDD .. for KBOS (Boston Airport) station .. there were 1385 HDD from 12/4 - 1/12 .. if 165gal were used, that works out to 0.119gal/HDD

RyanC

So the real question is

How do I know if this is "good" or not?  This is my first house wil oil heat; so  I dont know if I am burning a "normal" amount or way too much. 

RAF

My two cents

Compared to 300 gallons in 11 days  346 degree days your usage seems great.

It sounds like you have a three section boiler with a coil. That is the smallest oil boiler out there with a domestic coil as far as I know. I do not believe anyone is putting together two section boilers anymore.

85 nozzle may or may not be small depending on fuel pump pressure nozzles are rated at 100 pounds of pump pressure, as the pressure goes up so does the rating.( 20 year old boiler) my guess is your pump is at 100 pounds pressure.

If you have automatic delivery your fuel company's software should be able to give you a good idea how you are doing efficientcy wise based on degree days and number of days.Its interesting once you have that information to sit with a calculator and see how many hours a day your system fired.

RyanC

You are correct

I do have a small 3 section boiler and according to the tags left by the previous service company the pressure on the burner is at 100 and it is a 60 degree .85 nozzle.  The .85 does match the specs for the "smaller nozzle" listed by Burnham, but I think they specify a different degree.  What would be the reasoning for changing the degree on the burner?

RAF

Depends

I think on some units Burnham commended a 45 degree angle nozzle. Not everyone has them on the truck could be one reason. The other could be noise they may have down sized the nozzle and changed the angle to quiet the burner down should still give you about 85% with 0 smoke though.

My guess is that if you had the correct size nozzle in your boiler you might cut your fuel down a little as you might shorten your cycle times.  You would have to get a good base line on what you have now to see.