There are a few RO's that claim not to require a heated room, but most do. I'll let someone else address the ones that claim not to need heat. When I got my RO I had no heat. I bought an RO on wheels and store it in a well insulated room, barely large enough to get the RO into. I started by heating the room using 3 light bulbs @ 100 watts each. I still use that as emergency back up but I now have a propane wall heater installed, made by Housewarmer. It runs off a bulk tank I have for many other needs, originally a propane canner, finisher,hot water tankless heater and a weed burner torch (for lighting the fire). A few months ago I got a water jacket canner which uhas an electric 3000 watt element. The heater I have is only 8000 BTU and it has a standing pilot and requires no power. It is direct vent, exhausts out an inner pipe and pulls combustion air thru an outer pipe and it runs off a thermostat.
When I start my RO I'm firing the evaporator within 10-15 minutes. You will want an RO that does 250 GPH or more, upwards to 500-600 GPH. When I'm starting my RO I start by running it at a slightly lower pressure, which give me more concentrate and less permeate. As soon as my heat tank level is high enough, I turn the pressure up. This gives me less concentrate (but at higher sugar) and more permeate (the pure water removed from the sap.) If my head tank starts to get full enough, I simply close the fresh sap valve and at the same time I open a recirculate valve. this removes more water from the concentrate, thus raising the sugar %. It is quite easy to run in this manner.
Once you run sap thru an RO, you need to boil it right away or you must be able to keep the temperature of the concentrate down to 30-34 F, once sap is concentrated you not only concentrate the sugar, but you also concentrate the micro-organisims and if not kept cold enough it will spoil much faster that raw sap will.
RO's are rated in GPH, that is the amount of sap at 38 degrees it will process in an hour. The way I do it I concentrate til I have about 30 gal. in the head tank before I light the fire, by the time the evaporator is fully going I have 50 or so gal in the head tank and at that point I either run the pressure to match my evaporation rate or I run a little faster than the evaporator and then recirculate to remove more water.
I have a 3x8 and I generally fire it to boil about 70-75 gph. Before the RO I made between 6-8 qts/hr of syrup, I now draw 4-5 times that in syrup and I use way less wood. Before the RO the most taps I had was about 900 taps. Later I worked up to 1320 taps but since then I have scaled back to 750, not because the equipment couldn't handle it, but because I lost 3 workers as they graduated college and I was getting up in years (now in my 70's).
Before the RO I had one time when we boiled 21 hrs. a day for 2 days in a row and during that time I also sold 1150 gal of sap to another producer. Since the RO my longest boil has been usually 3-4 hrs and all sap is boiled, occasionally a 5 hr boil when the sap is running great, and I also boil sap from other producers on shares, the get back a % based on what the sugar % of the sap was and I keep the rest.
If you get a RO rated at 250 GPH at 2% sugar and take it to 8% sugar (mine will do that) you end up with about 62-63 gal of concentrate to boil, thus if you boil more than that in an hour you either need to run the pressure lower (get more concentrate and less permeate) or start farther ahead or get a bigger RO.
Tanks, at a minimum you need 1 sap tank, one head tank and 1 permeate tank. You should have 2x the hourly rating for permeate storage, because you use permeate to clean the RO.
I have a 250 GPH RO, use 3 sap tanks at the sugarhouse and 2 more on a trailer I use to haul sap for almost 1700 gal storage for sap, then a 150 gal head (concentrate) tank and a 1000 gal permeate tank and I never leave sap to process the next day.
Once you get an RO you will wonder how you ever got by without it.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.