Square footage of heat per heat mat

Anyone have any feelings/thoughts/data on how much square footage (or cubic footage I guess, but I’m going to assume we all have similar heights of pumice at play) one can utilize per 60" x 21" heat mat (or similar size). Obviously, it depends how much heat loss and energy I want to deal with and how much I care if a pot’s base is at 80 degrees or 77 or 75… But, if I’m not to worried about those variables within reason, can I rock an 80" x 24" heat bed with a mat like that, or should I play it close to the 60" x 21" dimensions?

If only I had more time to experiment! :slight_smile:

Thanks for any thoughts. I hope you are all well.


I built mine closer the pad dimensions. I think your 3" excess width is fine, but the 20" excess length it too large and you will end up with cold spots at the ends. The pumice does not conduct the heat very well.

I can’t speak to your actual question, but can offer a bit of anecdotal advise. If you can set your heat mat on a piece of foam. I had some foam that is 3/8"-1/2" in thickness. When I put that under my heat mat I saw a 50% increase in efficiency in terms of soil (in this case pumice) temperature compared to the ambient temperature. I don’t recall who exactly gave me this bit of advice, but it was a fellow Mirai member. Love this community!

My heat mats were just slightly smaller than the boxes that sat on them. Didn’t plan it that way, but it just kinda worked out. I had two mats with some overlap though when I needed to add a second mat.


Insulation is the best heating. If you prevent heat loss to the great sink in the ground you put it all to use in your bed. Neve4 used mats, but from my cables I’d assume there is not much of excess footprint you can use it on.

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Thank you all for your thoughts and taking the time!