you will likely have to change the efficiency settings. do you mean no sparge or first runnings? these mean two different things to me at least.
no sparge means that you don't run off, re-fill and run off again. essentially you don't rinse the grain at all. When I do no sparge I include a 'mashout' step that brings my water/grist ratio up really high, like 6-7 liters per kilo (about 3.5 qt/lb) then runoff. I get around 67% brewhouse eff doing this.
First runnings only means to me that you are building a partigyle recipe and not doing a second runnings beer. In that case you mash with your normal water:grist ratio and runoff whatever is there. If I calculate the brewhouse efficiency on the first runnings beer ONLY on a partigyle brew I get ~52-55%.
I don't really see the difference here. The only reason most partigyle beers use a "normal" water to grist ratio is that the first runnings beer is usually something big like a barleywine. If you're doing a first runnings beer for something with lower OG, your water to grist ratio is going to be higher but you'll still need about the same amount of total liquor to hit your desired volume (adjusting for absorption differences). You don't want to go too thin, so the mashout step is a good idea for anything above 2.5 qt/lb or so.
true, it depends on the gravity of the recipe. that is the main difference. However if you are calculating your efficiency that is what it primarily depends on in my experience.
When I am doing no-sparge it is for a small to medium beer. I'm not leaving a lot of sugar behind at that point. If I do no-sparge on a big beer though I am leaving enough sugar behind to make another whole batch of beer. so perhaps a difference in degree rather than kind but I still see a pretty significant difference.
So lets say this...
If at a high but not too high water:grist ratio you can reach your preboil volume, accounting for all boil off and grain absorption that your overall efficiency will likely be lower than if you can/have too add additional 'mash out' water to meet your volume needs.