Offer to buy them a few indoor portable heaters until you find a solution. 

Invelo is a true all-in-one solution for real estate investors, built with industry-proven best practices.

While the RentRedi's loaded with various toggles/buttons and affordable given the all-you-can-eat pricing, the interface is still very elementary and lacking in usability/design, which is often overlooked as a key determinant of whether your team actually adopts and fully leverages powerful management solutions like these.

You will need to work out a mutually-agreeable solution. 

I think your clients should think about this as short-term funding that they would need to pay back rather than a long-term solution for capital.

So @Mike S. is providing the perfect solution for you. 

I didn't even think about chatgpt for searching for even easier solutions!

But my solution in your case would be to frame out a dividing wall of 2x4s and either drywall or if the basement is prone to taking on water then I’d look for something waterproof as opposed to the drywall.

At that point, it's worth researching and finding a solution that better meets your needs.

If it holds up under these conditions, you've got a solid investment—better safe than sorry!