Does anyone know an alternative to Caldera 7 to use for heat transfer fluid? Is it just 100% Silicon oil?
Silicone HTF refers to the backbone of the molecule. Think of silicone as long chains that have things hanging off of them, including more silicone chains.
Those things hanging off of the backbone as well as the length of the chain determine the properties (viscosity, temp range, flash point, etc).
So not all silicone oil is the same but if you look at the SDS of caldera 7, it states somewhere to be formulated to be compatible with most silicone oils. If that is true, then i would match a new fluid based on temp range and ensure you’re buying a silicone based HTF and not hydrocarbon or mineral based oils.
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There are various silicone oils and HTFs out there that could work as replacements to caldera 7. Most of the oils are 20 cSt oils, though some with different viscosities would also work. Not all 20 cSt oils would be safe or suitable.
You’re very unlikely to find any that are substantially cheaper than Caldera, it’s about as low priced as any HTF with similar properties that I’ve ever been able to find.
Get ready to spend a lot of time reading data sheets and SDS, or just buy pretty much any other silicone based HTF.
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Ive used some stuff called super lube silicone oil b4, it was $390 for a 5 gallon, years ago. I know caldera is in the $600-700 range.
I ran the same heat exchanger fluid for atleast 3 years and saw no change. I even emptied all my resevoirs and put it back in the 5 gallon with a simple mesh filter. Looks practically brand new and it looks like i only lost about a half gallon from spills and leaky hoses over 3 years of constant use.
I also checked the heating elements on the resevoirs and they are squeaky clean. So nothing was scorched unlike plant oils like canola oil, which definitely showed scorching after a short trial period. (Which led me to invest into silicone oil, so i never have to replace it again)
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Duratherm S might be an option.
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In a completely sealed system this could work. I wouldn’t run it in an open bath, though. It’s got additives and stuff in it that you may not want to breathe.
It might be fine. It might not. I like my lungs, they’re worth more than a couple hundred bucks.
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Hate how exepensive this stuff is gotta buy. 5 gall tomorrow. I like my lungs tho so for open baths set around 120-140c, caldera is the right choice from what I read.
duratherm is designed for open baths as well.
its not cheaper tho is it?
it used to be like 3-400 but i just searched and it looks like its 6-7 now.
This whole “problem” was part of why I came up with the propane refrigeration and heating.
Anytime you heat or cool you either swap solvent or deal with volcanos as it warms up - or you are stuck buying stupid expensive thermal fluid…
Our propane based tech solves the single fluid and the heat/cooling thermal transfer all with one refrigerant and uses less power than traditional systems. 
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