What do people usually use in their fridges to warm beer? I'm still not convinced about heat mats!
many folks who use fridges to ferment (indeed many who build their own chambers as well) tend to use a heat lamp or light bulb in a paint can type setup. this only works for having one beer/temp range in the fridge at a time however, since the heat is applied to the ambient air in the chamber, rather than to the fermenter.. controlling multiple brews at a time would require multiple chambers. folks who run multiple fermentations in a single chamber/fridge will typically use multiple controllers and flexwatt/heating mats on each fermenter to control the temp individually.. (you set the fridge temp to the coldest fermentation temperature you have among all your fermenters, and then have individual heaters on the fermenters to raise the temps for brews that need to be warmer.. ie, 55f for lager and 65f for an ale)
https://www.homebrewtalk.com/forum/threads/diy-paint-can-heater-question.648148/
The key/reasoning for the lightbulb in a paint can thing is that incandescent light bulbs are cheap and put off a LOT of heat, but they also put off a lot of light/UV so to reduce the amount of UV/other light that comes in contact with your beer while it's fermenting the bulb is encased in a closed up metal can to prevent light from escaping.. you'd hate it if your heater skunked your beer before you even got a chance to taste it.
when you say "heat mats" are you talking about:
sprouting mats (
https://www.amazon.com/dp/B00S1VJ0OC/?tag=skimlinks_replacement-20)
or standard heating pads (
https://www.amazon.com/dp/B000FGDDI0/?tag=skimlinks_replacement-20)
or are you talking about flexwatt/heat tape type heaters: (
https://www.amazon.com/dp/B00DOZGLYM/?tag=skimlinks_replacement-20)
I'm no expert on this stuff, but in my mind, the concern is really about how much heat you put into the fermenter and in what locality/concentration.. the flexwatt stuff puts out a specific wattage per-foot of heater.. for example 20w/ft -- which mean (for that wattage) would be a 12inch by 11 inch piece of flexwatt.. which means you're putting 0.15 watts per square inch (less if you neglect to insulate) .. you could argue that a 40w light bulb in a can, or 50w infrared reptile heater in side a fridge would/could put out less watts per square inch into your fermenter, and I think you would be right since that heat would be spread out over the entire surface area of the fridge and the fermenter together.. but does that actually make a difference?
in my own system, fermenting 10g batches in 15.5g sanke kegs, the heat tape + inkbird 308 controller typicallly keeps my beer within +-1f of the set point. the heat side runs just long enough to raise the temp approx 1f. I believe you'll see more hysteresis with an ambient heater due to the residual heat in the chamber after the set point is reached. (the air temp and inside of the fridge will be warmer than the set point, since those things have less thermal mass and heat up faster.. )
While the heat is on, I can hold my hand against the heat tape without injury -- it's barely as warm as my hand. I can't recall when the last time I tried touching a 40w light bulb that had been running for a while, but I do recall it hurt quite a bit.
I'm not trying to sell you on any one method vs another.. you have to figure out what works for you.. all I'm trying to say is that flexwatt or directly heating the fermenter is not unsafe and does not cause concern with respect to beer quality. I believe the quality of your temp controller and your method of taking temp readings (ie, thermowell vs taped/insulated to the side of the bucket/fermenter) is more important than the heating method.. a simple 2 stage controller will have more hysteresis than a PID based controller, regardless of the type of heating/cooling method you choose.
I have had (recently even) heating issues with my setup, due to a broken temp controller. this would have been problematic if I had been using a light+can type ambient heater as well, so I figure it's good info.. basically my controller lost it's mind and decided to read the temp probe as being -5f -- and so it turned on the heat.. and basically left it on for a whole day.. when I went to check on it, the fermenter was sitting at 90+f.. I replaced that controller and have had no issues since. the cautionary tale here is that no matter what you choose, be sure to check in on it regularly to ensure that it's working how you want.
