Does stacking GPUs hurt performance?

[Amillercuts]

TLDR; If I have two hot GPUs stacked so one is exhausting onto the other and the later onto the PSU an inch below is this going to hurt performance significantly enough to warrant a bigger MOBO/Case?

So I have a RTX3080 and a RTX2070. 
I am using these for Redshift, a GPU accelerated render engine that can take whatever I can throw at it. 
Although I do game on occasion I know the 2070 isn't being used unless I point Nvidia PhysX or something at it. I see over a 1/3rd decrease in render times using both vs one card which is awesome, but I am trying to weigh the pros and cons.
My issue is these are hot cards and very close together on my small board under an inch of air between my 3080 and 2070. They are both blower style and I am worried that when setting a render to go often for over 8 hours at a time it will hurt the performance and lifetime of one or both the cards. Also wondering if a larger case/motherboard would help.
I'll be monitoring the cards in MSI afterburner but would love any tips/knowledge you all have. Thanks.





Sorry if this is common knowledge and I am being a noob. But didn't find much on here with a quick search.  

[RageTester]

Heat kills for sure, but GPUs should last years even at temps near throttling.

If noise is no trouble, you might as well leave case open and use PCI Express riser for the 2070, so it's completely outside the case.

[Amillercuts]

3 hours ago, RageTester said:

Heat kills for sure, but GPUs should last years even at temps near throttling.

If noise is no trouble, you might as well leave case open and use PCI Express riser for the 2070, so it's completely outside the case.

Noise isn't an issue, but I don't exactly want a card just hanging like an eyeball knocked out of socket. Have a buddy that thinks I should just use a test bench as a "case". Might be a middle ground. 

[jones177]

My last SLI setup was two GTX 1080 tis and I had no issues with it. Temps were fine as long as I did not overclock the cards. It was mainly used for video rendering.

 

I have a bench(Streacom BC1.1S) and have kept computers on it for months without issue so I would not think twice about using this as a rendering rig.

https://www.thermaltakeusa.com/core-p3-tg.html

 

I am a retired freelance 3D designer and for years I did CPU rendering with the sides of the case off and a floor fans pointed at them. I did this because when renders failed due to heat it was always in the middle of the night and it usually was a nightmare since the jobs had to go out the next day. Only my game design experience saved me since I know how to fake it.  

[RaviP]

Yeah, Stacking will increase temps and reduce performance. I would worry more about single PCIe cable you are using to power 3080. I think single cable rated for ~280 watts and EVGA 3080 GPU take upto 340~370 watts or even more than 400watts I guess.

[Sauron]

6 hours ago, Amillercuts said:

TLDR; If I have two hot GPUs stacked so one is exhausting onto the other and the later onto the PSU an inch below is this going to hurt performance significantly enough to warrant a bigger MOBO/Case?

You can test this yourself by tracking the temperatures and clock speeds to see if/when they are or are not boosting. It's not really possible to make a blanket statement on this.

 

Obviously they will run a bit hotter than they would otherwise but if you have good airflow it may not make a big impact on your performance.

 

If they aren't boosting you should first try adding a few fans (if possible), a larger case should not be necessary. You can also try running with your sidepanel off just to see if it makes a difference.

[Amillercuts]

6 hours ago, RaviP said:

Yeah, Stacking will increase temps and reduce performance. I would worry more about single PCIe cable you are using to power 3080. I think single cable rated for ~280 watts and EVGA 3080 GPU take upto 340~370 watts or even more than 400watts I guess.

Interesting didn't know that might be an issue! Thanks.