I 2nd Roy’s Comments!
Recommend Removal of such an appliance. These units do not vent products of combustion of natural gas / propane when burned to the outside of the living space.
Your readings are a warning .
CO levels (acceptable) depend on which government / safety organizations too. CO is a Killer period.
Time and exposure rates kill people. A small amount over a long period can be just as bad as a large amount in a short period.
Here are some numbers for you:
EPA Max exposure levels @ 9 PPM for 8 hours and 35 PPM for 1 hour!
OSHA 50 PPM for eight hours and 200 PPM for no more then 15 minutes.
This maybe for a factory setting .
As you can see they vary quite a bit… BUT don’t forget the rest of the house…
Is there a propane / natural gas water heater or clothes dryer or Stove??
How about the main source of heat for this home? What type is it?
All these factors can add to the CO levels in this house.
From what I read my area highly recommends these types of appliances be removed.
What is a life worth …