DOE Heating Capacity Maximum

HM389

I am in need of a new oil fired steam boiler. My EDR is around 61MBH. What should the maximum DOE heating capacity be?

This is what I found:

Weil-McLain has a SGO-3 with a 114 DOE heating capacity

US Boiler thru Burnham has a MegaSteam MST288 with 92 DOE heating capacity.

I don't want a system too big causing short cycling. Are these I found too big? Is there anything else out there smaller? Any other recommendations?

ChrisJ

https://forum.heatinghelp.com/discussion/202539/doe-heating-capacity-maximum

You'd be best with one that falls somewhere between 70,000 and 80,000.

That said, I'd go for the Megasteam and just have the burner tuned at the rate you find best for the system. As far as I know, that should be able to be tuned for an output of 70,000 +- and if that's not enough, it can be increased. Remember, if it takes time to get going, and slowly fills the radiators without building pressure, that's a good thing, not a problem. The last thing you want is rapidly building pressure. You'll know it's right when it can run for an hour straight and stay under 1/4 psi (in my opinion).

The MegaSteam MST288 is probably the best oil fired boiler you're going to find for your system, period.

Jamie Hall

It's a lot easier and less trouble to compare your EDR (which should be in square feet rather than BTUh) to the boiler square foot rating for steam than to start converting stuff to BTUh…

Steamhead

@ChrisJ said: "The MegaSteam MST288 is probably the best oil fired boiler you're going to find for your system, period."

This.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1871020#Comment_1871020

Not really.

Its just math.

EBEBRATT-Ed

I agree with @Jamie Hall to stem any confusion between input, output, DOE capacity just use square foot EDR.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1871033#Comment_1871033

And that leads to people thinking the boiler is too small because it doesn't quite support enough EDR which is because the number had the 33% built into it. So a boiler that's 30% over the required output gets up sized again.

61,000 * 1.15 to 1.33 = 70,000 to 80,000.

HM389

Can someone double check to see if I did the math right.

I had a total of 250 EDR of square feet x 240 to give me a total of 60,004

Is this 61MHB?

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1871029#Comment_1871029

And no one ever makes a mistake when it comes to math

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1871064#Comment_1871064

Yes in this case M means thousand.

mattmia2

note that most systems need far less than a 30% pickup factor

Jamie Hall

And in the situation here, you can see that the Megasteam MS288 has more than enough capacity (288 square feet vs. your 250) without doing any math at all — just reading the label…

EdTheHeaterMan

I don't get why you need to convert the EDR to BTU, then determine if you need the select Input of 105,000 BTU(0.75 x 140,000/gal rated fuel, or 92,000 BTU DOE capacity, or NET AHRI 69,000 BTU output. Only to get back to a boiler that has a rating of 288 SqFt NET Steam rating.

If you want to get fancy and dial in the firing rate to 0.66 GPH by using a 0.50 nozzle at 175 PSI. You will need a combustion analyzer to properly tune the burner with this specification, but it will work.  Ask me how I know?

If you like to do math and hope you didn't make a mistake carrying the 1 to the next column, then calculating the difference between the actual input rating of the nozzle and the higher pressure adjustment of the fuel pump. Here is the equation:

The relationship is proportional to the square root of the pressure ratio because the flow through a nozzle is governed by orifice flow principles. Once that math is done and you get the actual firing rate of the burner, then measure all the combustion parameters in order to provide proper combustion for at least one season until you can return for the annual maintenance for the next season. You must also determine if the lower firing rate of the boiler will impact the exhaust temperature adversely.  Once you have done that you can now use the actual 0.66 GPH x 140,000 BTU fuel = 92,400 BTU Gross Input.

That would make the 92,400 BTU gross Input convert to about DOE Heating capacity of 81,000 BTU.  That 81,000 DOE would convert to AHRI NET rating of 60,750 BTU.  That 60,750 AHRI NET would convert to AHRI 253 NET Sq Ft steam.  

After all those calculations were completed which will have taken some time you can then do this magical math related prediction:

1. Pick a number between one (1) and ten (10)  not including one or ten. 
2. Multiply that number by 9
3. Now you have a 2 digit number correct?
4. Add the two digits together
5. Now subtract 5 from your number answer.
6. Using the alphabet as a cipher where 1 = A and 2 = B and so on… select the letter in the alphabet that corresponds to your number 
7. Think of a European country that begins with that letter.
8. What was the last letter of that country?
9. Think of an animal that begins with that letter

Spoiler Warning

 Now I wonder if you were thinking of a Kangaroo in Denmark

DCContrarian

Koala.