RTX 4090: reduce a workflow's memory demand before changing hardware
The practical alternative to chasing a VRAM modification is to discover which stage exceeds your existing card's capacity. A workflow that fails during decoding needs a different investigation from one that cannot load its model at all, even when both end with an out-of-memory message.
Find the failing stage
Begin with the standard RTX 4090 specification: 24GB of device memory. Keep the original failing graph, then make a separate diagnostic copy. Record whether failure occurs while loading weights, encoding text, sampling a latent, decoding the image or running an enhancement node. Preserve the full error report and the selected model filenames.
Do not diagnose capacity from an error message alone. Incompatible model components, unsupported precision and custom-node failures can also interrupt a run. Establish that a maintained basic workflow runs successfully before applying a collection of memory flags.
Make the smallest useful workload
In the diagnostic copy, use one output at a time and remove optional enhancement stages from that copy. Retain the original graph unchanged. Choose a smaller output only if it still answers the creative question. A successful small composition test can establish model compatibility without pretending to satisfy a final print-resolution requirement.
Change one parameter and save the result with its graph. If lowering image dimensions makes sampling work but decoding still fails, record that distinction. Keep separate notes for a task that now completes and a task that meets the intended visual quality.
Treat memory options as tradeoffs
ComfyUI's troubleshooting guide documents low-memory operation, reduced batch size and disabling previews as possible interventions. Use the instructions applicable to your installed version. Do not combine every flag from unrelated tutorials: a controlled baseline makes both regressions and improvements attributable.
Offloading moves some work or data away from the accelerator; it does not increase physical device memory. It can introduce transfers, system-RAM pressure or longer completion times. A tiled decoder should be evaluated at the decoding stage, with inspection for seams and changes in output, rather than advertised as a universal saving.
Set a stopping rule
Write the acceptable output dimensions, quality and waiting time before testing. If the reduced-memory route satisfies them consistently, a capacity change is unnecessary for that job. If it only produces a compromised preview, preserve that limitation in the project record.
When the required model or deliverable still does not fit, compare a supported larger-memory device or a controlled remote run against the complete job requirements. Include transfer, setup and data-handling costs. This page recommends a diagnostic sequence, not a particular purchase or an unverified hardware modification.