One option to reduce possible heat losses in a combustion process consists of reducing the temperature of the flue-gases leaving the stack. This can be achieved by:
●dimensioning for the maximum performance plus a calculated safety factor for surcharges
●increasing heat transfer to the process by increasing either the heat transfer rate, (installing turbulators or some other devices which promote the turbulence of fluids exchanging heat), or increasing or improving the heat transfer surfaces
●heat recovery by combining an additional process (for example, steam generation by using economisers, see Section 3.2.5) to recover the waste heat in the flue-gases
●installing an air (or water) preheater or preheating the fuel by exchanging heat with flue- gases ( see S ection 3.1.1.1). Note that the manufacturing process can require air preheating when a high flame temperature is needed (glass, cement, etc.). Preheated water can be used as boiler feed or in hot water systems (such as district schemes)
●cleaning of heat transfer surfaces that are progressively covered by ashes or carbonaceous particulates, in order to maintain high heat transfer efficiency. Soot blowers operating periodically may keep the convection zones clean. Cleaning of the heat transfer surfaces in the combustion zone is generally made during inspection and maintenance shutdown, but online cleaning can be applied in some cases (e.g. refinery heaters)
●ensuring combustion output matches (and does not exceed) the heat  requirements. This can be controlled by lowering the thermal power of the burner by decreasing the flowrate of fuel, e.g. by installing a less powerful nozzle for liquid fuels, or reducing the feed pressure for gaseous fuels.

減少燃燒製程可能的熱損失的方法之一，是將煙氣排出煙囪時之溫度降低。這方法可以下列方式來達成：
●設計尺寸規格以達到最大績效，同時兼顧過度負荷時安全因素的計算。
●使用提升傳導效率的方法或增加傳熱面積提升熱能。這些方法如裝設擾流裝置使流體擾動以增加熱交換率。
●結合另個附加製程，如使用節煤器以回收煙氣中的廢熱。
●裝設燃燒空氣(飼水)預熱器或利用煙氣換熱將燃料加熱。
●如玻璃、水泥生產製程中需要高溫火焰，則需要採用空氣預熱。
●用水預熱的方法也會用在鍋爐飼水或地區取暖的熱水系統等場域。
●清潔傳熱表面逐漸堆積的灰塵或積碳以維持其清潔，可提升傳熱效率。
●定期操作吹灰器可維持對流區域清潔。
●通常燃燒區熱傳導表面的清潔作業會在停機檢查保養時執行，但有些情況會在生產線上做清潔工作，如煉製業的加熱器。
●確認燃燒的產出熱能要與熱需求匹配，而且不要超過需求。可利用燃料的流入量控制以減少燃燒器送入的熱量，例如燃油燃燒可以裝設一較小動力的噴嘴，燃氣燃燒可以降低燃料壓力等方式來達到控制的目的。

Reducing flue-gas temperatures may be in conflict with air quality in some cases, e.g:
●preheating combustion air leads to a higher flame temperature, with a consequence of an increase of NOx formation that may lead to levels that are higher than the emissions limit value. Retrofitting an existing combustion installation to preheat the air may be difficult to justify due to space requirements, the installation of extra fans, and the addition of a NOx removal process if NOx emissions exceed emission limit values. It should be noted that a NOx removal process based on ammonia or urea injection induces a potential of ammonia slippage in the flue-gases, which can only be controlled by a costly ammonia sensor and a control loop, and, in case of large load variations, adding a complicated injection system (for example, with two injection ramps at different levels) to inject the NOx reducing agent in the right temperature zone
●gas cleaning systems, like NOx or SOx removal systems, only work in a given temperature range. When they have to be installed to meet the emission limit values, the arrangement of gas cleaning and heat recovery systems becomes more complicated and can be difficult to justify from an economic point of view
●in some cases, the local authorities require a minimum temperature at the stack to ensure proper dispersion of the flue-gases and to prevent plume formation. This practice is often carried out to maintain a good public image. A plume from a plant's stack may suggest to the general public that the plant is causing pollution. The absence of a plume suggests clean operation and under certain weather conditions some plants ( e.g. in the case of waste incinerators) reheat the flue-gases with natural gas before they are released from the stack. This is a waste of energy.

降低煙道器的溫度有時候會與空氣品質有所衝突，這情形說明如下：
●預熱燃燒空氣有時會導致火焰溫度高出許多，這會使得更容易形成NOX，進而導致NOx排放量超標。
●若要在既有的燃燒設施裝設空氣加熱器可能要考量某些因素，如所需空間、裝設額外的風機、增加將超標NOx去除的製程等。
●要特別注意的是，將超標NOx去除的製程是以液氨或尿素注入方式，這會觸發氨氣洩漏到煙氣中，這情形只能用高成本的氨氣檢測器和一控制迴路系統來管制。若為負載變化較大的情形，還要增加另一套複雜的注入系統注入脫硝劑到正確的溫度區。
●如脫硝或脫硫氣體淨化系統只能在一定的溫度區間工作，所以為了要符合排放標準必須裝設這些系統時，如何安排氣體清淨系統和熱回收系統則頗為複雜，而且以經濟的觀點來看也很難做抉擇。
●在某些情況下，地方政府會要求工廠煙囪必須在一最低溫度排出以確定煙氣適當的擴散並避免白霧化形成，實務上也必須做，以維持良好公眾觀感。
●在公眾眼裡沒有白霧化排出表示工廠操作良好且清淨。因此，有些燃燒工廠如垃圾焚化廠在天候條件不好時，會用天然氣將煙氣再加熱後，從煙囪排出，如此就造成能源浪費。

The strategies above,  apart the periodic cleaning,  require additional investment and are best applied at the design and construction of the installation. However, retrofitting an existing installation is possible (if space is available).
Some applications may be limited by the difference between the process inlet temperature and the flue-gas exhaust temperature. The quantitative value of the difference is the result of a compromise between the energy recovery and cost of equipment.
Recovery of heat is always dependent on there being a suitable use (see Section 3.3).
See the potential for pollutant formation, in Cross-media effects, above.

上述幾項策略，除了定期清理之外，需要在這些設施原始設計和建造時做額外的投資，既有設施如空間夠也可以改裝。
技術上採用可能會限制進入製程和煙氣排放的溫度差，這差異的量化值是能源回收效率和設備投入成本間妥協的結果。
熱回收必須要有適當的用途。
潛在汙染物質的產生，參見上述交互效應所敘述。

Payback time can be from under five years to as long as to fifty years depending on many parameters, such as the size of the installation, and the temperatures of the flue gases.

投資回收年限可能是五年以下，也可能長達50年，要看設施規模、煙氣釋放溫度等參數而定。

Energy Efficiency (2009) 3.1.1