HRM frustration

HRM and treadmills are not created equally, and will calculate the calories differently. You can choose the one that's more convenient, or you could err on the side of caution and use the lower of the two values to avoid eating back too many calories. Monitor your progress with either the HRM or the treadmill for a while and if your progress is too fast/slow, switch to the other one. It's probably more important to be consistent.

HRM and treadmills are not created equally, and will calculate the calories differently. You can choose the one that's more convenient, or you could err on the side of caution and use the lower of the two values to avoid eating back too many calories. Monitor your progress with either the HRM or the treadmill for a while and if your progress is too fast/slow, switch to the other one. It's probably more important to be consistent.

^This.

It is better to pick one measuring tool and use it consistently. Since your HRM monitor will be the same no matter what exercise you use, choose that. Here's one way to adjust for HRM errors; there are others. YMMV.

1. Calculate your TDEE or MFP calorie target and swear to live by it for at
least twenty-eight days.

2. Make recording your calories eaten and calories burned your new religion
for at least four weeks.

3. Depending on your goal (losing, gaining, maintaining) you should be able to
reasonably predict your weight in one month. At the end of the month, look
at the target vs. what actually happened.

4. Now you know whether your HRM is off or not and have a rough idea of
how much, percentage-wise.

For example, you do all of this and instead of six pounds lost, you only lose five. Figure that's 3500 calories. Take your total exercise calories over the month, subtract 3500 and get your "adjusted" exercise calories. This will tell the percentage error in your HRM. Use it to adjust your HRM whenever you exercise.

Repeat as necessary.

What is important is consistency. IF you track input calories and output calories over time, along with your weight, you can figure out the fudge factor needed for decent predictability.

HRM and treadmills are not created equally, and will calculate the calories differently. You can choose the one that's more convenient, or you could err on the side of caution and use the lower of the two values to avoid eating back too many calories. Monitor your progress with either the HRM or the treadmill for a while and if your progress is too fast/slow, switch to the other one. It's probably more important to be consistent.

It's even better to be consistently accurate, which is the case with most commercial treadmills (if you don't hold on).

Trying to diagnose if a HRM that takes so few datapoints as inputs is producing more accurate caloric burn estimates than a treadmill is impossible online. There are far too many variables in play that are not accounted for here.

Not really. As stated above, you only need workload and body mass. It just so happens that the energy prediction equations for walking, incline walking, and running are relatively simple, have been validated, and are easy to program into the treadmill console. Most major commercial brand treadmills should give consistent readings, that are as accurate as you can get without more expensive equipment. That assumes you have: entered your weight and are not using the handrails for support. I have seen research that suggests that the running equations might overestimate by 8-15% depending on speed, but that is still more accurate than most HRMs.

If one is on a commercial treadmill, and HRM calories are significantly higher or lower than the TM calorie reading, it is a pretty good indicator that your HRM is not set up properly.