Forge version: 35.1.11
Mods:

• Advanced Chimneys
• Applied Energistics 2
• Astral Sorcery
• AutoRegLib
• Bamboo Everything
• Bookshelf
• Botania
• Chisels and Bits
• Create
• Curios Forge
• Enchantability
• Engineer's Decor
• GeckoLib
• Endertech
• Glassentials
• Immersive Engineering
• Immersive Petroleum
• Immersive Posts
• Immersive Railroading
• Just Enough Items
• Mana and Artifice
• Macaw's Furniture
• Mekanism
• More Red
• Nature's Aura
• ObserverLib
• Patchouli
• Path Under Gates
• Platforms
• Psi
• ShetiPhanCore
• Storage Drawers
• The One Probe
• TrackAPI
• UniversalModCore

What I expect: When I power an External Heater placed directly next to a vanilla Blast Furnace or vanilla Smoker, the vanilla Blast Furnace or vanilla Smoker should light up just like a vanilla furnace.

What really happens and how to reproduce: When powered, the External Heater does not light the vanilla Blast Furnace or vanilla Smoker

This is intentional behaviour, it only heats the standard furnace since those two already have a speed increase.

That^