Compare the spaces
Measure basement and upstairs temperatures at similar times. Is the complaint cold air, cold floors, drafts, or a particular room? Record outdoor conditions and the thermostat schedule.
Ask what the previous system deliberately heated and whether the new design includes the basement. Save the original proposal and load calculations. An excluded space should be visible in the design rather than discovered during winter.
Do not close grilles or add openings to redirect heat without assessment.
Separate heat delivery from heat loss
Ask the HVAC provider to check output and how heat reaches the affected spaces. Adequate overall output does not establish that a particular room receives enough heat.
Floors above unconditioned spaces can contribute to heat loss and cold floors. DOE's building-science guidance treats the floor and air barrier as part of the insulation boundary. DOE floor-insulation guidance.
Have an appropriate building-performance or insulation provider assess basement walls, floors, air leakage, and moisture before recommending work. The treatment depends on whether the basement should be within the heated part of the house and on its actual construction.
Do not assume adding heat alone addresses dampness or a building defect.
Compare the complete correction
Options may include correcting heat delivery, improving the building boundary, or appropriate supplemental equipment. Ask what each changes, what remains unresolved, and which qualified provider owns the work.
Include water pipes and temperature-sensitive equipment when discussing needed basement conditions. If freezing is a concern, arrange prompt assessment and protection with the appropriate trade.
Your next step is a temperature record and review of the conversion's intended coverage. Request a recommendation connecting basement and upstairs findings, with costs and responsibilities separated. That gives you a reason for the correction rather than a general efficiency claim.