While there is nothing to stop you from grouping identical items as a single asset for depreciation purposes, I strongly advise against it. Here is my reasoning: You are in the second or third year of the asset's useful life and one of the items stops functioning and has to be taken out of service. How are you going to account for the disposition of half of an asset on your next tax return?
Also, wall heaters are not, in my experience, particularly expensive items. You might want to just consider expensing them in the current tax year rather than setting them up as depreciable assets. Effective with the 2016 tax year, the IRS raised the threshold for expensing, rather than capitalizing, tangible assets to $2,500.
For more information, please refer to IRS $2500 Safe Harbor
Expensing Threshold Eff. 01/01/2016.
