Why shoud hot water boilers not be oversized?

Tom Andrews

Hello,



I was wanting some information on why a hot water boiler should not be oversized.  Specifically, I am interested in the efficiency issues.  Is there data available regarding fuel consumption and short cycling? 



Thanks.



Tom

CMadatMe

Common Sense

Don't mean you don't have any but thing about it. If I need 60K btu's and I install a boiler that is 100K, which by the way is only needed on my design days, where does the other 40K go that I paid to burn? Those extra btus wasted get larger as the days get above the design temp.



Short cycling also causes more maintenace and service issues. Bigger is not better.

NRT_Rob

If you're interesting

there are commercial white papers that reference 50% efficiency losses from short cycling. ORNL's domestic hot water testing from boilers shows 30% efficiency in the summer on cast iron and high 50's/low 60's even from mod/cons... that's primarily because of worst-case cycling losses (all residual heat is wasted).



on top of that you have lifecycle costs to consider.

Tom Andrews

Where to get papers?

Thanks - that's what I was interested in - actual published data.



Do you know where I might access some of the commercial white papers?  Anyone else beside ORNL?  Appreciate the direction.  Thanks

NRT_Rob

here's one

that you might like

Tom Andrews

Perfect

That was perfect.  Thanks very much Rob



Tom

NRT_Rob

sure

fun read. it's for commercial boilers, so I would hesitate to translate it directly to residential scale boilers. but it establishes the fact that it matters, at least.



I can't wait for datalogging tech to sink in price a bit more so fuel use vs heat delivered can be compared on more systems!!

Big Ed_4

Sized for the largest load ...

Which in most residential is domestic hot water ...if the boiler is used for it as well as heat..