select @@version
go

-- Query1 : Tested on MS SQL Server 2014 at sqlfiddle.com
select x.id,
       x.val,
       format(avg(x.val) over (partition by x.id
                               order by x.rn
                               rows between 2 preceding and 2 following
                              ),
              'N1'
             ) as mov_avg
  from (
            select id, val,
                   row_number() over (partition by 1 order by (select 1) asc) as rn
              from data
       ) x
go
  
-- Query2 : Tested on MS SQL Server 2014 at sqlfiddle.com
with x (id, val, rn) as (
    select id, val,
           row_number() over (partition by 1 order by (select 1) asc) as rn
      from data
)
select x.id,
       x.val,
       format(avg(x.val) over (partition by x.id
                               order by x.rn
                               rows between 2 preceding and 2 following
                              ),
              'N1'
             ) as mov_avg
  from x
go

with x (id, val, rn) as (
    select id, val,
           row_number() over (partition by id order by (select 1) asc) as rn
      from data
)
select x1.id as id,
       x1.val as val,
       convert(decimal(6,1), sum(x2.val)/count(x2.id)) as moving_avg
  from x as x1
       join x as x2
       on (x2.id = x1.id and
           x1.rn >= x2.rn - 2 and
           x1.rn <= x2.rn + 2
          )
group by x1.id, x1.rn, x1.val
go

C:\data>
C:\data>sqlcmd -S <server_name> -U <login_id>
Password: <entered_password_here>
1>
2> select @@version
3> go
 ------------------------------------------------------------------------------------------
Microsoft SQL Server 2008 R2 (SP3-OD) (KB3144114) - 10.50.6542.0 (X64)
        Feb 22 2016 18:07:23
        Copyright (c) Microsoft Corporation
        Enterprise Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1)
 
(1 rows affected)
1>
2> --
3> with data (id, val) as (
4>     select 'H1', 1.2  union all
5>     select 'H1', 2.3  union all
6>     select 'H1', 5.5  union all
7>     select 'H1', 6.6  union all
8>     select 'H1', 8.7  union all
9>     select 'H1', 4.1  union all
10>     select 'H1', 6.4  union all
11>     select 'H1', 7.8  union all
12>     select 'H1', 9.6  union all
13>     select 'H1', 3.2  union all
14>     select 'H5', 50.1 union all
15>     select 'H5', 54.2 union all
16>     select 'H5', 58.8 union all
17>     select 'H5', 60.9 union all
18>     select 'H5', 54.3 union all
19>     select 'H5', 52.7 union all
20>     select 'H5', 53.8 union all
21>     select 'H5', 60.1 union all
22>     select 'H5', 59.9 union all
23>     select 'H5', 59.4 union all
24>     select 'H5', 57.1
25> ),
26> x (id, val, rn) as (
27>     select id, val,
28>            row_number() over (partition by id order by (select 1) asc) as rn
29>       from data
30> )
31> select x1.id as id,
32>        x1.val as val,
33>        convert(decimal(6,1), sum(x2.val)/count(x2.id)) as moving_avg
34>   from x as x1
35>        join x as x2
36>        on (x2.id = x1.id and
37>            x1.rn >= x2.rn - 2 and
38>            x1.rn <= x2.rn + 2
39>           )
40> group by x1.id, x1.rn, x1.val
41> go
id val   moving_avg
-- ----- ----------
H1   1.2        3.0
H1   2.3        3.9
H1   5.5        4.9
H1   6.6        5.4
H1   8.7        6.3
H1   4.1        6.7
H1   6.4        7.3
H1   7.8        6.2
H1   9.6        6.8
H1   3.2        6.9
H5  50.1       54.4
H5  54.2       56.0
H5  58.8       55.7
H5  60.9       56.2
H5  54.3       56.1
H5  52.7       56.4
H5  53.8       56.2
H5  60.1       57.2
H5  59.9       58.1
H5  59.4       59.1
H5  57.1       58.8
  
(21 rows affected)
1>
2> exit
  
C:\data>
C:\data>