Unit Heater

[G.P.]

We are replacing out unit heater at the shop and it is currently an 80K BTU gravity vertical vented unit. 
Considering the Reznor  UDAP 100 (Power vented) or UDAS 100 (Sealed/separate combustion with vertical concentric kit).
Our shop is used for storing our tools and loading our trucks.  The heater running for an hour a day or maybe for a full day once a week or so.
Would you guys spend the extra $1k (unit and venting) for the separate combustion model or don't see the need to?
Any advice would help as we do not yet install any heaters/furnaces and stick to mostly gas lines to basic appliances.
Thanks again,
George

[slo-115]

Unless the building is super air tight i wouldn't worry about it. Just install the standard UDAP, i have installed at lest 30 units, other then one that had a bad circuit board outta the box they have been trouble free.