Surge calories way low compared to zip

[SunsetRunner]

I recently had a fitbit zip that on average showed me burning about 100 cal every 10 min. I upgraded and got the Surge but now it says i'm burning on average 40-50 cal every 10 min. I don't understand why there is such a huge gap when my profile has been set the same for both fitbits (gender, height, weight, stride length). Can someone please explain this to me? It doesn't make sense. I used to hit 10k steps at least 4 days a week....I have yet to hit it since I got the Surge 2 weeks ago. The struggle is real and it's highly discouraging. I now miss my Zip. 

Also, the step count and everything else seems to be pretty close to the Zip. It's only the calorie count that is real different. 

Thanks for any advise on this. 

[HelenaFitbit]

Welcome to the forums @SunsetRunner and congratulations on getting your new Surge!

All Fitbit trackers show an estimated number of calories burned based on your BMR (Basal Metabolic Rate) which is calculated using your height, weight, age and gender from your Fitbit account. However; Your Surge works differently than your Zip when it comes to calculating your calories burned because your Surge measures heart rate. This calorie burn estimate also takes heart rate into account, so it can provide you with a more precise calorie count for your activities.

On the other hand , if your Heart Rate is showing too low on a daily basis; there's a chance that we might be losing a constant connection from your PurePulse monitor. Please check these tips from our Helpsite to improve your HeartRate readings. 

Hope this helps! Let me know if you have any questions