How accurate is HRM when it comes to calorie burn.

It's very accurate, and as accurate as it's going to get compared to any other method out there. Just make sure your stats are entered into it correctly and that you update your weight as you lose. Also, remember, depending on your resting metobolic rate, you need to subtract a certain amount of calories per hour from what your HRM says. For example, my RMR is about 80 calories, meaning I'd burn that in an hour laying on the couch staring at the ceiling. So if my HRM says I burned 580 calories, I subtract 80 calories leaving 500 as what I burned due to exercise.

I think mine is accurate.. more so than a few others. Mine has a chest strap.. but some seem a bit .... generous, i guess.

I have the Poloar Ft7 and got to say its pretty accurate. Everytime i have a weightloss i update it to make sure and only wear it when working out

It's as accurate as it can be from just measuring your heart rate. A fully assessment requires being fully wired up with a respiratory meter and all those other instruments you see people in laboratory wired up with that give a full assessment of metabolic rate.

One thing that may be giving you a high burn is that it incorporates the calories you'd be burning at rest too, so don't count these twice. If your BMR is 1500 calories in 24 hours, you'd be burning 62.5 calories at rest. If you run for an hour , your HRM might say you've burned 600 calories, but you should record 537.5 as MFP already takes your BMR into account.

Hope that makes sense!

Does the chest strap go below the boobs or above.. i'm confused. The instructions say chest muscle but shows the bottom of the pectoral muscle on a man! UGH! HELP!

It's very accurate, and as accurate as it's going to get compared to any other method out there. Just make sure your stats are entered into it correctly and that you update your weight as you lose. Also, remember, depending on your resting metobolic rate, you need to subtract a certain amount of calories per hour from what your HRM says. For example, my RMR is about 80 calories, meaning I'd burn that in an hour laying on the couch staring at the ceiling. So if my HRM says I burned 580 calories, I subtract 80 calories leaving 500 as what I burned due to exercise.

I totally understand, but I think it a little differently.

You burned 580 calories in an hour, and RMR is 80 calories, so 580-80 = 500 calorie burn as you stated above.
But, during that hour you burned almost 10 calories / min on average, not 1.333/min like in RMR

When most people finish exercising they are not cooled down when they look at their HRM for that 580 total.
So for the next 10-15 mins while they are cooling down, getting their heart rate down, most people will burn another 80 calories very easily. You can't just shut your body down from burning 10 calories / min.?

So, is all that extra math needed?

It's as accurate as it can be from just measuring your heart rate. A fully assessment requires being fully wired up with a respiratory meter and all those other instruments you see people in laboratory wired up with that give a full assessment of metabolic rate.

One thing that may be giving you a high burn is that it incorporates the calories you'd be burning at rest too, so don't count these twice. If your BMR is 1500 calories in 24 hours, you'd be burning 62.5 calories at rest. If you run for an hour , your HRM might say you've burned 600 calories, but you should record 537.5 as MFP already takes your BMR into account.

Hope that makes sense!

Ditto the resting calroies should be backed out, but I would argue that you should be backing out maintenance calories, not BMR, as if you did not workout you would be doing something else (sitting, walking, etc) and BMR is the amount you burn in a coma. So you should actually back out maintenance (may only make 0.25 to 0.5 cals/minute difference from using BMR, but it will make a difference the longer your workouts are) So if you BMR is 1500 and you are sedentary your maintenance will be around 1800 which is 75/hour (1800/24, 12.5 higher than using BMR only) so if your HRM says 600 in one hour you should really only enter 525 (600-75) into MFP to eat back.

To get your maintenance calories go to your goals page and look at calories burned from normal activity, that is maintenance calories.

Also, a question do people leave the timer on during weights the whole time or do you stop and start the watch at each set. I leave it running even when I'm resting between each sets. Is this bad? Inaccurate when measuring calories burned in a work out?

Thanks

Anyone?

Also, a question do people leave the timer on during weights the whole time or do you stop and start the watch at each set. I leave it running even when I'm resting between each sets. Is this bad? Inaccurate when measuring calories burned in a work out?

Thanks

Anyone?

You can leave it on for circuit training, very little rest, may slightly overestimate the burn, but if you stop while you are resting during no circuit strength training you will under estimate, while leaving it on will overestimate. HRM's do an okay job estimating calories burned while strength training, but are way more accurate and the embedded calculation in the HRM is designed to give you calories burned doing aerobic (cardio) activity.

They vary, to be honest. I have a HRM chest strap with my Garmin 305, and also one with my Polar F6. The Garmin is always higher...WAY higher, to the tune of 1,000 extra calories. Garmin is known for being high on the caloric expenditure estimation. Polar is the industry standard for accuracy in HRM-based calorie tracking.