Two bedroom return vents got covered during renovation. Is it critical that I open them back up?

New home owner here. We had the first floor renovated before we moved in, and had new sheet rock put up everywhere. I noticed after we moved in that the return vents in each of the two bedrooms were no longer there. Turns out they were unintentionally sheet rocked over. I wonder if this might have happened because the return ducts in the basement are just the space between the floor joists, closed in from the bottom (house is from 1950). There might not have been metal casings extending to the return grills in the wall. I really don't know. Regardless my question is, how important is it that I open them back up? I have an American Standard Freedom 80 forced air natural gas unit. There are two returns in the main part of the house, one of them is a double-wide return vent, one is normal. The heating worked fine in April and May since we moved in, but I wonder if these returns being closed would stress the furnace or cause it to be less efficient. Last thing I want to do is ruin a relatively new (2016) furnace. Opening the vents back up will require some sheet rock, trim work and paint to be re-done.
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This is very simple. The volume of air put out by the furnace needs to be returned to the furnace.
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On 6/7/2018 7:40 PM, catalpa wrote:

Assuming the original installer did the job correctly, the return vents need to be opened back up, especially as they are in two different rooms.
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replying to Steve, Millennial HVAC wrote: Reducing the airflow across the furnace can be serious, and may cause the heat-exchanger to prematurely fail. The temperature difference across your furnace should be no more that usually more that 40 degrees F, the data tag on the unit will usually specify the design temp differential. I suggest you contact a licensed hvac contractor in your area to evaluate your situation. If you happen to be in the Fort Worth area, you should visit my company's website at www.millennialhvac.com
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