James. Do not have answer to your question but you probably need manufactures installation manual. Here is some interesting reading on these units from MA code.

UNVENTED GAS FIREPLACE:
: Installation. A permit shall be obtained from the head of the fire department and the local or state gas inspector having jurisdiction for the installation of all unvented propane or natural gas-fired space heaters. Said permits shall be conditioned upon final inspection and approval of installation by the head of the fire department and the local or state gas inspector having jurisdiction. A copy of the manufacturer's installation/operating literature shall be submitted with each permit application. Before operation, the Head of the Fire Department and the local or state gas inspector shall inspect the installation for compliance with 527 CMR and 248 CMR (Board of State Examiners of Plumbers and Gas Fitters). Unvented propane or natural gas-fired space heaters shall conform to ANSI Z21.11.2, be equipped with an oxygen depletion safety (ODS) shutoff system and be listed and approved in accordance with 248 CMR. Unvented propane or natural gas-fired space heaters shall be installed in accordance with their listings and the manufacturer's instructions. Proper clearances to combustibles shall be maintained. In no case shall the clearances be such as to interfere with combustion air and accessibility. Installations shall be of a permanent type, with a permanently piped fuel supply in accordance with 248 CMR. LPG appliances shall be subject to the storage requirements in accordance with 527 CMR 6.00.
Portable unvented propane or natural gas-fired space heaters shall be prohibited.
Unvented propane or natural gas-fired space heaters shall be prohibited in bedrooms and bathrooms. Space heaters shall be properly sized for the room or space of installation, but shall not exceed a maximum of 40,000 BTU input per room or space. In occupancies with an unvented propane or natural gas-fired space heater, at least one listed carbon monoxide detector shall be installed and maintained in any room or space where said heater has been installed in accordance with the manufacturers instructions. Any building wherein said heater is to be installed shall, as a precondition to such installation, have working smoke detectors installed and maintained in accordance with the requirements of 780 CMR (State Board of Building Regulations and Standards) in effect at the time of construction or if no said requirement was in effect at the time of construction, installed as provided for in M.G.L.c. 148, §26E. In rooms and buildings served by an unvented propane or natural gas-fired space heater, a primary source of heat, which is operable, shall be permanently installed and maintained in said building in accordance with 105 CMR (Department of Public Health). Sellers of unvented propane or natural gas-fired space heaters shall provide to each purchaser a copy of 527 CMR 30.00 upon sale of the unit.

Maintenance and Operation. The maintenance and operation of unvented propane or natural gas-fired space heaters shall be in accordance with the manufacturer's instructions. The manufacturer's instructions shall be left with the appliance and made available for any public official. Any malfunction of an unvented space heater shall forthwith be reported by the owner to the head of the local fire department.

UNVENTED FIREPLACE COMMENTS:
: The use of un-vented gas fireplaces or heaters should be discouraged due to the possible negative effects of their operation in a cold climate.
: The potential for introducing unwanted carbon monoxide into the living area is certainly a disincentive to having these appliances in the home, but the addition of a large amount of moisture to the indoor air is an absolute certainty.
: Excess moisture can condense on windows or, even worse, it can be driven by positive pressures inside the house into attics and wall cavities where it can condense and allow mold and rot to develop.

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Dave