3900 calorie TDEE???

HRM tend to say in their booklet that they are not intended for extended wear and are not accurate for non-cardiovascular activity.

I use www.1percentedge.com/ifcalc/ for my TDEE calculator.

Wearing a HRM all day is not going give you an accurate figure. Calculators like the one posted will be a good guesstimate and a good place to start. Supposedly something like a fitbit or whatever can track daily calories but I haven't used one personally.

HRM become increasingly inaccurate for long periods of low heart rate. I would not use this as the way to calculate your TDEE. Use a good calculator then adjust after observations over a couple weeks.

That seems too high. I input your numbers (with 27% BF) and got:

Sedentary (little or no exercise, desk job) 2375
Lightly Active (light exercise/sports 1-3 days/wk) 2721
Moderately Active (moderate exercise/sports 3-5 days/wk) 3067
Very Active (hard exercise/sports 6-7 days/wk) 3414
Extremely Active (hard daily exercise/sports & physical job or 2X day training, i.e marathon, contest etc.) 3760

http://www.fat2fitradio.com/tools/bmr/

If you workout everyday and have a strenuous job then maybe. I lift 4 times a week and do sports/run the other days of the week and I'm around 3300. Get me out of my desk and that'll blast passed 3900 I'm sure.

HRM not meant for TDEE, try a body bug or use calculator, sounds high to me.

HRM don't measure calories they guess them from your heart rate - the guess is wrong.

How do fitbits manage to be more accurate for this sort of thing?

They start with a foundation like those TDEE calculators - your BMR.

Sadly it's the Harris formula, least accurate one, but still.

They then measure movement, basically walking, stairs, ect.

And walking is much more accurate for calorie burn than HRM, because it literally takes so much energy to move so much mass at so much pace - which is what the FitBit figures out.
Your HR on such an effort merely shows your fitness level and ability to provide oxygen and if burning mainly fat or carbs to provide such energy.

So as you are guessing, they start losing accuracy on stuff more intense than walking or slow jogging, where personal efficiency starts being a bigger factor.

Oh, if you have a club foot and move much differently than normal efficiency, it'll be off too then.

HRM don't measure calories they guess them from your heart rate - the guess is wrong.

Well, they can be pretty good, they can be pretty bad. To say it's a guess that is wrong would imply they aren't right for anyone, which isn't the case either. Does more right than wrong surprise you?

2 studies on fact they can have some accuracy to them. One is Polar funded study.

http://www.firstbeat.fi/userData/firstbeat/download/white_paper_energy_expenditure_estimation.pdf

http://www.braydenwm.com/cal_vs_hr_ref_paper.pdf

Did you workout at all at any time you were recording?

HRM's are more accurate at measuring calories burned when you're an an aerobic heart rate zone, not while at rest. I imagine it would be terribly inaccurate when your heart rate is below 60%.

On top of that, you probably don't know your true max heart rate. Unless you've actually been tested, you don't know it. Any numerical calculator for max heart rates have been proven to be off by more than 20bpm. A 5 bpm difference is enough to severely skew your calorie consumption.

I didn't know that there is a relationship between max hr and calorie consumption.
How can max heart rate be tested?

Basically, you need to push yourself to your body's absolute limit. Symptoms of reaching your max HR are: puking, seeing stars, blacking out, etc. Never, EVER do it without supervision. It could kill you.

Also, for the reasons mentioned above, speak to your physician first and get a thorough physical/check up done. If you have any issues with your heart at all, DO NOT DO IT.

There are various books and other sources that tell you ways to test you max HR, so I won't elaborate on a routine you can use on here. If, for whatever reason, you cannot do the test, then the next best thing would be to do a Lactate Threshold test, which is similar, but won't kill you. Just use the number from that as 75-80% of your max HR and you'll be in the ballpark. Again, look for a good source for a routine to follow, to test that.

I know from personal experience that MHR calculators don't work. 2 years ago, I joined a running group to try to get back into shape. This was 1 year after injuring myself and sitting on my butt. My calculated MHR was 196. We were climbing a hill, and from my mountain biking days, I felt we were going too slow, so I booked it up the hill. I hit a HR of 202, and I didn't even feel like I was stressing myself too much. I probably could have hit 210.