In 1" pipe, you should easily have a flow rate between 3.4 and 3.8 ft/second at gravity feed (far less pressure).  

When we gutted our house and our second SFR we pumped air in lines and made sure it didn't loose pressure obviously if you do you have a leak.

Passive systems are better, though, because they avoid the continuous cost of electricity to run a fan and a loss of conditioned air caused by low pressure below the slab.

I refuse holes in my siding and if they must, I require a dish be mounted with a deck kit or on a post in the yard.

Please find one who is not afraid to explore the downside dangers with you--one who wants to help you buy five houses and not just one--one who is doing enough business to not ever send any sales pressure your way.  

Pressure them to release it - remind them they have no outstanding debt on the books, why wouldn't they?

We had some inward movement of the walls due to hydrostatic pressure.  

If you do it after appraiser goes out and sees it: Get some licensed contractor to throw some cheapo baseboard heaters in.If you do it before appraiser goes out and sees it: Throw some cheapo baseboard heaters in that looks like it could have been done by a licensed contractor.Needs to be a permanent heating system, so you will want ones that you drill screws into the baseboard to mount them.EDIT: This works in CA, but now that I think about it this may be something state-specific.

Some markets have pressure on the landlord to do this.

And don't be pressured by the Seller to wire your closing funds in until you've been assured that this has been sorted out.