This post is about low-pressure boilers burning buildcraft fuel post-v8.3.
Here is the table that tells you how long a burn you need in order to beat 3.125 total MJ/HU (so, be more efficient than a combustion engine.) You will see in the graph why the data for the 36LP are lacking.
Code:
boiler time fuel max eff.
1LP never n/a 2.99
8LP 7.77 58 3.20
12LP 4.31 46 3.33
18LP 3.37 51 3.55
27LP 2.9 58 3.95
36LP notsure 4.44
Here is the graph. Left axis: MJ/HU, like in the second series of graphs in Omicron's original post. Right axis: fuel usage. This is included to remind people that 2 hours in a 36LP is much much more fuel than 2 hours in an 8LP, and therefore also much more MJ, which if you don't have a use for, is wasted. I assumed that fuel usage is still linear w.r.t. time during heatup; if that was an error please let me know.
You will note the kink in the 36LP efficiency graph. This was a kludge made necessary by the fact that Forecaster's calculator (thanks to Forecaster for a neat tool) will not tell you how much MJ is produced if the boiler does not finish heatup. I noticed that the other curves intersect so I drew a line right to the intersection to complete the 36LP efficiency curve. The other curves begin when heatup is finished and are so inefficient before that point that I didn't investigate any further. (That was a result of my error. New 36LP curve in attached graph. All the efficiency curves start when heatup is finished.)
For all boilers except the 36LP this is not a big deal because when heatup is over efficiency is still low. So surprisingly this implies that only the 36LP boiler is efficient before it's done heating up, that it reaches efficiency (which I define here as "better than a combustion engine") before any other engine. If I interpret this correctly, the 36LP would always be the dominant choice—if you had something to which to apply its enormous power output.
The intersection of the efficiency curves means that for any burn time over 2 hours and 26 minutes, the larger the boiler, the more efficient it gets, faster. This is so pronounced that, contrary to my expectations, you're better off burning 58 buckets of fuel in a 27LP than an 8LP; you'll burn it faster
and more efficiently (cf. the table at the top of the post). I could do another graph with fuel on the x-axis to see which boiler size should be used for a given amount of fuel, but it looks like
for anything higher than 46 buckets, the answer is just, 36LP (and for anything lower than that the answer is, combustion engines). (Wrong; see post #254 for how this all shakes out.)
I didn't investigate the HP boilers at all so... I will if there is demand but if someone who knows the math well can tell me that that is a waste of time, tell me. Thanks.
I'm satisfied this is enough information to choose a boiler, with one missing piece: does the boiler really consume just as much fuel just staying hot as it does when it is being harnessed?
Maybe at a future point in time.
