The double furnaces do not use the Steel Plate Productivity Technology.
This block in data-updates.lua fixes it.

if mods["space-age"] then
table.insert(data.raw.technology["steel-plate-productivity"].effects, { type = "change-recipe-productivity", change = 0.1, recipe = "double-iron" })
end

Thanks

Can you submit a PR? :)

Raid, i've got this fixed on my end but i'll hold off on the PR till you reply to the post about reducing the cost of the electric research to be back in line.
As i'll do all as one PR and version change to make it easier.

Ay word on if this change will be implemented into the mod itself?

I don't really have many resources currently.
I forgot to answer mat1k: Still interested in the PR if you'd like to make one

I don't really have many resources currently.
I forgot to answer mat1k: Still interested in the PR if you'd like to make one

I was waiting on you to answer at the post about the reduced cost to match the changes in cost to the base game research that happened around 2.0

https://mods.factorio.com/mod/DoubleFurnace/discussion/67984f14b8bf3c84c65db3c4

I'm head to work but can do a pull request for one or both over the weekend.
I have tested both changes already in my testing install and they work fine.

Excellent, if you already have tested the changes then I'd like to see them

PR is done for this.

Merged