Let us first determine the optimal heat exchanger:

The superior heat exchanger is the one that provides the required performance, within design limitations at a minimal cost.

The major design limitations are:

Maximal length of a heat exchanger.

While offering the same heat transfer area, the longer heat exchanger with a smaller shell diameter is less expensive then a shorter one with bigger shell diameter.

Maximal flow velocity.

The higher velocity of flow results in an improved heat transfer rate and smaller heat transfer area.

Maximal pressure drop. 

The higher pressure drop permits a higher velocity of flow.

Size, location and construction of connections.

Your system is unique. To simplify the piping and proper fit to your system, you would prefer to have a heater with connections of your choice.

Price versus quality.

In general, we will work with and within your limits. While we always optimize a heat exchanger for the lowest price, in some cases we recommend  the selection of more expensive materials and design for a higher quality product.  For instance,stainless steel tubes have superior mechanical properties and corrosion resistance.  When stainless steel tubes are TIG welded to the tube sheet, the joint efficiency equals one.  In many cases, these advantages dictate the usage of more expensive stainless steel tube.  Another example is usage of a channel head which is more laborious and costly to produce than a bonnet head. However, a channel head makes it very easy to check and plug leaking tubes without dismounting the piping.  A channel head permits the repair of a tube bundle in fuel oil suction heaters without draining the fuel oil from the storage tank.