> For the complete documentation index, see [llms.txt](https://support.powerio.com/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.powerio.com/hub/codesys-hvac/en/hvac-library/functionblocks/components/fastheating.md).

# FastHeating

## `FastHeating` (FB)

FUNCTION\_BLOCK FastHeating

### Short description

> Activation of a fast heating mode (controlled variable: room temperature)\
> \
> Typical application: Activation of the fast heating mode in the operation of an air handling unit

### Representation

<figure><img src="/files/87aa23f33723b356b2245c6e67fac0c7478dba92" alt=""><figcaption></figcaption></figure>

### Function description

#### General

This function block controls the activation of the fast heating mode (*xEn* = TRUE) by comparing the room temperature *rRoomTemp* with the room setpoint temperature *rSetPtTemp* when the ventilation system is active (*xRegAHU* = TRUE).\
The fast heating mode can also be activated independently via the input *xCoolOutProtectionEn* activated.

#### Enable / disable of the fast heating mode *xEn*

| *xReqAHU* | *rRoomTemp*                          | *xCoolOutProtection* | *xEn* | Notes                                                      |
| --------- | ------------------------------------ | -------------------- | ----- | ---------------------------------------------------------- |
| FALSE     | X                                    | FALSE                | FALSE | Fast heating mode via air handling unit and input disabled |
| TRUE      | > *rSetPtTemp* + **rSwitchOffPoint** | FALSE                | FALSE | Fast heating mode disabled due to room temperature         |
| TRUE      | < *rSetPtTemp* + **rSwitchOnPoint**  | FALSE                | TRUE  | Fast heating mode enabled due to room temperature          |
| X         | X                                    | TRUE                 | TRUE  | Fast heating mode enabled via input                        |

Legend: X = any

### CODESYS

InOut:

| Scope       | Name                   | Type   | Initial |
| ----------- | ---------------------- | ------ | ------- |
| Input       | `rSetPtTemp`           | `REAL` |         |
| Input       | `rRoomTemp`            | `REAL` |         |
| Input       | `xReqAHU`              | `BOOL` |         |
| Input       | `xCoolOutProtectionEn` | `BOOL` |         |
| Output      | `xEn`                  | `BOOL` |         |
| Input Const | `rSwitchOffPoint`      | `REAL` | -1      |
| Input Const | `rSwitchOnPoint`       | `REAL` | -2.5    |


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://support.powerio.com/hub/codesys-hvac/en/hvac-library/functionblocks/components/fastheating.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.