How much Glycol (tranfer fluid) should I buy?

Mthek

I am ready to drain and refill the Alde system.  
Any ideas on how much transfer fluid I should buy to complete the job?

Sharon_is_SAM

What model trailer do you have?  400 or a 320?  

Mthek

2016 320

Sharon_is_SAM

Less than 2 gallons for the 320.  I just read another owner’s post regarding their exchange.

Sharon_is_SAM

Actually, if you use the pump system to drain it, it sounds like you need 2.5 gallons.  Less if you just drain it thoroughly and add it back in.

Ron

I used 2.5 gallons for a drain/flush. I didn't flush with distilled water, but I do believe that it was a fairly complete flush due to a slight color difference between the old and the new fluid.  I did drain first to get most of the fluids out of the boiler before the new went in.  Just my theory.

ScottG

IIRC, if you calculate the volume of the heating loop/expansion tank and add that to the published capacity of the boiler itself, it comes up to ~2.5 gallons. So @Ron, I think your empirical observations are spot on.

At least this is true for the older 320s. With the expansion tank now relocated to the front of the trailer, there might be a little more heater hose to account for. And, obviously, 400s may be a different story as well.