If your bedroom temp is 70 you will need an additional heat source.
Your UTH is only there to provide a hot spot. This will primarily aid the snake in digestion after a meal.
Your ambient temps will hardly be affected by the UTH. 70 is too cool for an ambient temp for a BP and will probably result in your snake not eating or if it does eat it will not digest properly and possibly regurgitate it's meal. Temps that low will also likely lead to Respiratory Infection.
This is why you will need an additional heat source.