Instruction: Given a question and the related document, and generate the answer to the question based on the information provided in the document.

Input:
Question: Is this a ventless system. I want to use it in my insulated garage.
Document: I had mixed feelings about buying an opened product, but upon receiving and installing the heater, those mixed feelings were gone. The heater works perfectly and heats my garage very efficiently without any issues. Everything came with the product that was supposed to and i am very pleased.
I thought I could get away with no venting on this based on descriptions but discussed this with a plumber and the consensus is, since I live in MinneSNOWta with all the snow melt off in the garage, with no venting there would be a ton of moisture from the snow melt with no where to go so if you buy it, don't forget to budget in the cost to vent!
This keeps my 3 bay garage warm and toasty , Very easy to Install , no power needed for stat
Thermostats that use a 650 mV control are available, but many are set up to control larger furnaces and use 12/24V or even 120 V AC, so be careful if you need a new or replacement thermostat. One of my local home improvement stores carried a 650 mV thermostat (both had several as catalog items), but they both had a number of 12/24v DC and 120v AC thermostats in stock.
I purchased a used unit and it looks like new. I have only given it a three star as i haven't had it installed yet. It looks good.
I would give 5 stars for the heater, but the included thermostat is JUNK, and Mr. Heater, a long-respected company, is shooting themselves in the foot with this t-stat.
After installing both units, I found that 1 was quite sufficient to keep my 24' x 30' x 11' storage building warm (about 50 F). Some observations include that an 11' tall roof is almost too low for these heaters, as the recommended clearances are fairly substantial.
After unpacking I found a dent and crease in the upper housing and a corner of the reflector bent up. It requires a separate thermostat to operate (not included) . Figured the cheaper sale price was because this looks more like a scratch and dent  sales item. Still isn't up and running yet as I haven't made the second trip to the hardware store.
Unless your building is very 'leaky', consideration for additional ventilation is needed and likely necessary. This does not add that much to the heater run time.These heaters and their associated thermostat (one came with a thermostat, the other did not - new units should have one) are powered by an built-in thermopile, a group of thermocouples that generate a 650 mV signal as long as the pilot is on.
This heater needs a shield for the pilot light. It has the right flame length per instructions but the slightest breeze blows it out. Needs to be relight each time it cycles off. Working with mfg for a fix.
Answer: I have this system in my insulated garage and I put a 10x10 vent near where I hung it. Also I put a carbon dioxide detector to be safe. Heater works great!!