Boaphile rack heating problem

[asarodd]

I've been having a problem Im trying to figure out with the temps in my 6 tub rack. Everything I've have read is about the bottom shelf running colder but mine is exactly the opposite. My top shelf (#1) is the coldest, in fact all the other shelves are really close to each other only varying within a degree.

My rack is set up in my bedroom closet in my apartment. My room temps have been between 74-79. On the day I ran these tests it was 79. The rack I have is a used rack with used flexwatt. How much it was used is unknown to me but I did have to disassemble everything to scrub it clean.

The flexwatt is a single piece of 4 inch that starts at the bottom and works its way up. Its about 11 feet long. Im running it off a herpstat2. The herpstat probe is on the bottom shelf taped to the top of the flexwatt beside a tub and I have checked its accuracy with the acurite i use in my test tub. I have another acurite on shelf #2 to monitor the flexwatt temps. I use an empty tub as my "test" tub with an acurite inside and the probe taped to the inside floor of the tub to see what the hotspot is with no substrate as some of my snakes like to burrow in it anyway.

I have the herpstat set to 93 degrees. With the test tub in the bottom shelf (#6) I get a hot spot of 92.8 after letting it sit awhile. So there is little loss of heat with this tub. Moving up the temps vary. Shelf #5 is 92.5, #4 is 92.8, #3 is 91.9, #2 is 93 but #1 is 89.

I have raised the herpstat up to 94 in an attempt to get #1 warmer. Shelves #2-5 all raise about a degree as expected but #1 sits at 89. During the testing I have noticed some shelves spike up a degree or 2 higher then what the herpstat is set too but then settle. I understand how flexwatt creates heat and its not perfect but is it known the be this variable?

Has anyone else had this top shelf problem or do I have some failing/worn out flexwatt? I cant imagine that my room temps are creating a one shelf problem. Im thinking about replacing it with THG heat tape. Just wanted to get other opinions before I pull this rack apart.

[Darkbird]

Try switching the accurites around and see if they give the same readings in the new spots. If the top shelf still reads low, you may have to pull the flexwatt and check it for breaks in that last section, as you might be getting no heat from it.

[bcr229]

Remove the tubs, let the heat tape run for a bit, and then measure the temperature of the heat tape. If it's consistent on every level then the tub on top may have a bow in it that permits more air to get between the heat tape and the bottom of the tub, so it will be cooler. Have you tried swapping the tubs around to see if that makes a difference?

[asarodd]

Yeah I have been using one exact tub as the "control tub" to check these temps to eliminate any variations in tub structure. Nothing with the tub and temp probe inside changed. The only change was which shelf it was on.