Free Water Mist Program by Alan Ashfield


FREEWATERMIST is a new, comprehensive and completely free "Windows" program for the hydraulic calculations of NFPA 750 Standard on Water Mist Fire Protection Systems (2015 Edition) as follows :-

FreeWaterMist Demo 1

Click here for download information and a quick tutorial about this new program or continue to scroll down this page for further details ...

FREEWATERMIST is a very simple, "point and click", fully interactive 3D layout program following the NFPA 750 Rules where you draw the pipe sections, starting at the pump / cylinder unit, out to the operating nozzles protecting the appropriate rooms or spaces.

Apart from some general data about the job and the various design parameters, each pipe is defined by its type, size, length, direction and any fittings / special items. Each nozzle is defined by its "K" factor, minimum pressure and optional area of coverage and I have kept the amount of actual typing to a minimum by offering selections of possible replies that you simply select with the mouse.

Note there are no node numbers to specify and all loops are found automatically, so you don't need to watch any videos, nor attend 2 day training courses, to find out how to use this program but you must know how to design the pipework arrangement, placing and spacing of nozzles of set types with known "K" factors etc. before applying it to your projects.

I suggest you start with 'Demo 1' or 'Demo 2' as these demonstrate all the features of my software and are reset to my data each time you select them so it does not matter if you make any incorrect changes or edits whilst trying out FREEWATERMIST.

User Interface :-

If you have used any of my other 18 FREE programs, you will know I am not a fan of 'menus' - they are usually too small and cryptic, so you have to click on them to find out what those options actually do and don't even mention 'icons' with their little pictures that you are supposed to know what they are before you click on them, especially if they don't have 'hints'. I much prefer to show all options and features on the screen, the one you are always looking it when using the program so if a particular action is not there, it is because you can't do that at this particular time eg. trying to 'Calculate' when you haven't entered any nozzles yet. The following screen shot shows the 'Demo 2' example illustrating the items detailed below :-

FreeWaterMist Demo 2

All the functions of FREEWATERMIST are arranged in two areas along the top and left hand sides of the screen which vary as you proceed through the various operations - File options - Drawing views and labels - Job options - Pipe options - Pipe Data. These therefore do not obscure the actual drawing which fills up the rest of the screen, especially when adding or editing pipes as I will demonstrate below. In fact, only the 'Job Data' and 'Database' details pop-up in the middle of the screen (with some warning / error messages) as they are just too wide to fit anywhere else. So you will find ...

File options :-


Just select this button to quit the program and return to your Windows Desktop. You do not have to save the data for your project as this is all done automatically.


You should have already sketched out a pipework design on a sheet of paper or a CAD layout drawing (usually in 2D but we need a 3D layout to cope with changes of elevation) and mark on the changes of pipe type, size, lengths etc to the nozzles protecting the area(s) under consideration in accordance with the NFPA 750 Rules. The program will give a short explanatory message and prompt for 34 questions about the project where I have filled in a number of responses which may, or may not, be applicable so you should review and change them if required. The drawing will then show one pipe (just to get you started) and you will be in 'Edit' mode to change it as you desire. There is a more extensive description and an example of this on the tutorial page that may be of interest.


This just asks for the name of a previously entered job (none to begin with so select 'Demo1' or 'Demo2' if the first time you are using FREEWATERMIST) to get the familiar "Open Dialog" display. You can use the various directory options to choose another folder or library if the initial one is not where your job is stored - perhaps on a network or USB memory stick. When a file name is typed in or selected (with the extension .3WM), click on "Open" and it will then be read in and shown on the drawing screen - see 'Pipe Options'.

Save as

This only comes up when a job has been read in and allows you to rename the file to make a copy before or after any major changes / additions or to keep a copy in another part of your computer or network. FREEWATERMIST always makes a .BAK version of your job each time you read it in.

Demo 1 or Demo2

I have provided 2 examples to help you evaluate my program and quickly show you how to use and apply it to your projects. Demo 1 is a generic low-pressure example and I suggest you just experiment with the various job, drawing and pipe options without actually changing anything and why not try clicking on 'Calculate' to see what happens :-

FreeWaterMist Demo 1

Demo 2 shows a high pressure system, with areas / densities specified and especially note the placement of fittings (TT not used on branch lines) :-

FreeWaterMist Demo 2 fittings

Just select these in turn and run through all the various options as described on the rest of this webpage. These 2 files are reset every time you select them so you can freely make any changes, edits, additions etc. you want, to try out all the various options as it does not matter if you screw them up completely!

Drawing views and labels :-

Plans, elevations and isometrics

This option allows you to select the required Plan, Front, Rear, Right or Left elevations or the Top-Left, Bottom-Left, Bottom-Right or Top-Right isometric views of the pipework / nozzle drawing. If you hover your mouse over the list-box, a short hint will confirm the direction of view. During data entry, as you move the 'arrow' cursor around the plan, its "X" and "Y" co-ordinates will be shown to aid in getting the correct nozzle spacings. As you move the "arrow" cursor around any of the four isometric views, the "X", "Y" and "Z" co-ordinates of the pipe junctions are shown.

Demo 1 views

Zoom in / Zoom out

When you first see the drawing, it will be shown full size. To view at a larger scale, just click on Zoom In to see a plan (if not already shown) with a message 'Click on any pipe / nozzle to centre plan around it ...' so just move the mouse cursor to the required area and click the leftmost button.

Demo 1 zoom in

The approx 3m area around that point will be given with the hint along the top saying 'Now zoomed in to the area chosen - "Zoom Out" to full size or select other views as required ...' so you can click on Zoom Out to go back to full size view or select different elevations, isometrics or another zooming point as needed.

Demo 1 zoomed in


You can view about 28 different key indicators - type, size, bores, lengths, fittings etc. to be shown, one at a time, next to the individual pipe sections / nozzles, on the current view. Simply click on the heading to see the full list, each with the minimum / maximum values so far, as needed. These will also change in sequence as you enter or amend pipes as described later.

Demo 1 labels

Job options :-

Job Data

Click on this to view the questions about this project and various design parameters. Just type in or overwrite the current reply to each and press the {tab} key to move to the next question or click the mouse at the appropriate point, just like a normal spreadsheet. A 'hint' along the bottom of the screen provides more information about the specific question and shows the range of numbers required. Any amendments made will be automatically saved when you click on 'Close' and the drawing redone if necessary. Please give consideration to Q22, 23 , 24 to 27 and Q31 if you have prepared a different database file (see next). If you change Q18 to 20 about the nozzles, then the program will ask if you wish those values to apply to the existing 'Usual' nozzles or only for newly entered ones.

Demo 1 Job data


Click on this to view the list of pipe types, sizes, internal bores and fitting equivalent lengths in the file name indicated. You may need to use the scroll bar across the bottom to see the remaining columns or make it full size, to see everything. You can easily have several such files for the different types of projects you may get involved in so can have them specific to your country or company. These can be kept private or Emailed to me to put them up on this webpage to permit other users to have the same data.

FreeWaterMist database

There are 3 "pages" across the top of the screen so you start with 'Pipe bores in mm and fitting equivalent lengths in m' where there is a spreadsheet-like display so you can move the highlighted cell around with the {arrow} or {tab} keys or just clicking your mouse in the part you want to amend and a hint across the bottom describes each in more detail.

You can also click on 'Add another pipe type' to specify two names, Hazen-Williams "C" factor and roughness in mm. You will then have to enter the list of internal pipe bores for this new type (or 0 if not applicable to that nominal size) before it can be used in your projects.

You can select 'Add another pipe size' if any additional sizes, bigger or smaller, are needed for your projects but will need the internal bores for all the existing pipe types (or 0) and equivalent lengths for all the existing fitting types (or 0) or else there is no point in doing this.

You can also use "NotePad" or similar to amend this .TXT data file if you prefer. Click on 'Close' when you have viewed / amended the database as required.


This will start, and quickly finish, the calculations for the system specified and the drawing will show the flow rates in the pipes and at the nozzles unless any are under the minimum pressure quoted based on the pump / cylinder design parameters where a 'pop-up' message will describe the problem. You can use the various 'labels' to see other details on the drawing as summarised on the left or you can select 'View' for more extensive summaries. You will also get some pop-up warnings about pipes with no flow not feeding any nozzles, water velocities over 20 m/s, over 10 bar pressure drop in a pipe and over 500 bars at nozzles if you have lots of undersized pipes.

FreeWaterMist Demo 1


This will produce some 2D and 3D DXF files for reading into a CAD program and a 'pop-up' message will give you their file names and other information.


When you click on this option, the drawing will be replaced by the full results presentation, as described in the NFPA 750 Rules with 110 nozzles or pipes per A4 page. The little 'hint' will confirm that you can press the 'up' or 'down' arrows or the 'Home', 'End', 'PgUp' or 'PgDn' keys on the right on your keyboard to move through these screens of information. You can also click on the top half to move up or the bottom half to move down as I find this easier. Your mouse wheel will also scroll up or down a few lines at a time. Most lines of information will be in grey but some may be in red, blue or green to highlight certain items mentioned in the 'Calculate' part. Note that the summary is still shown on the left hand side giving an overview of the results.

Demo 1 results

The following 2 options are now shown under 'Job options'.


When you have finished viewing the results, select this to return to the drawing exactly as you left it so you can choose other views or labels or edit the pipe / nozzle data as required. You can always select 'Results' again to step back to this display.


This can either produce a hard-copy on your chosen printer or generate a PDF file if you have already loaded a pdf-driver (free from or similar) in order to Email such files to other parties if required. Alternatively, you may prefer to get them to download my FREEWATERMIST program so you can just Email your text-only .3WM project file and database (if different from my standard) so they can see all the 3D drawings, interactive zooming, informative labels and options rather than staring at lots of sheets of paper with thousands of numbers on them!

Calculate after edits

During the data entry and amendment part you may be carrying out several operations on the network and its layout so you don't want to be interrupted with superfluous pop-ups or messages and FREEWATERMIST does not do that. However, after you have done the calculations you may find it necessary to change a few pipe sizes so if you 'tick' this check-box, the program will recalculate the system and show a summary on the left, to assist you in making the correct changes, every time you amend one or more of the items of pipe and/or nozzle data. If you wish to see the full results presentation, just click on 'Calculate' to redo the sums and then on 'Results' as before.


The best way to learn how to use these options, is to play with my 'Demo 1' and 'Demo 2' examples as it doesn't matter if things go wrong as they are reset to my data every time you click on them.

Click here for download information and a quick tutorial about this new program

Pipe data (visible only for 'Add' or 'Edit') :-

This screen shot shows the Edit pipe data option for 'Demo 1' and shows how the questions are grouped on the left hand side without obscuring the drawing :-

Demo 1 edit


Select the appropriate type of pipe from the list shown as they can be all the same or different in various parts of the network as required. A hint describes it in more detail if you hover your mouse here. If a specific pipe type is not shown, then you can add it with the 'Database' option.


Select the nominal size of pipe for this section, normally reducing as you move away from the water source so one does not usually have a section supplied from one of a smaller size except where the system is looped. If a specific size is not shown, then you can add it with the 'Database' option but you will need the bores for this, and the other pipe types as well as the equivalent lengths for the various fittings.


Type in the centre-to-centre length between fittings, either horizontal for pipe slopes under 45 degrees or vertical for pipe slopes over 45 deg, ie. the total change in elevation. Press the {tab} key when done and you don't have to enter the full number of decimal points so 3 will be shown as 3.000 and different pipe sections are required between nozzles or junctions (elbows and tees) of different directions, pipe types or sizes.


Select the run of this pipe from start (nearest the supply) to end (feeding another pipe or a nozzle) as North, North-East, East, South-East, South, South-West, West, North-West, Up, Down or another based upon the length entered. If not at 90 or 45 degree compass points, then select the last option, whereupon the next question will be prompted. If you get the direction the opposite way round to the previous pipe (so it doubles back on itself eg. 'Down' after 'Up' or 'East' after 'West'), then the program will detect this, move the pipe end by 0.5m in X,Y and Z and show it in a different colour, so that you can click on that (or the previous) one to correct the problem.

Run angle

If one of the above directions is not applicable, you can type in the exact angle as a compass direction from 0 = North, eg. 30 or 305 degrees.

Slope in degrees

This is not asked for Up or Down pipes but only for directions of horizontal or near vertical pipes and is typed in as a positive number (eg. 6) where the pipe slopes upwards from start to end (end is higher than start) or a negative number (eg. -7.4) where the pipe slopes downwards from start to end (below the start). Leave blank or enter 0 if pipe is run flat (no slope) with the length / direction given and press {tab} when done. In all cases, the program will calculate the 'actual' pipe length, up or down the slope for the pressure drop calculation eg. a pipe 3m in plan up a 5 degree slope is really 3.011 m long.

Fitting 1

Select the appropriate fitting usually at the start of this pipe section, either 'None' if straight through tee along a branch line or as the elbows, tees etc. quoted in NFPA 750. Again my examples show what is required, especially that you always ignore the fitting on which any nozzle is mounted. The "hint" will show the actual fitting equivalent length in metres based on the NFPA table, the HW-C factor (if different from 150), the bore in mm with respect to CuK tube and if the pipe type description has the word 'threaded', when it will be multiplied by 2.

Fitting 2

Where there is more than one fitting in this pipe section (where it connects into another pipe forming a loop) or several control valves, you can select this second fitting here or leave it as 'None'.


For special components in this pipe section which you will possibly never use. If there is a fitting where you cannot specify an equivalent length, enter the "K" factor (flow L/min divided by pressure drop in bars all squared) and K, eg. 500.00K, and this can also be applicable for orifice plates (if permitted) or partially closed valves to shut down a looped main.

If you wish to specify a hosesteam or hosereel allowance as a constant flow rate, then type in the L/min flow and L, eg. 120.00L, for the program to add this to the flows in all the pipes from this one back to the source.

If you have a really long length of pipe, say 100m, on this job then if you enter it as the full length, it will considerably distort the drawing making it difficult to view pipes of 3m or less, so you should put the "Length" of the pipe (as above) as, say 10.000 m, and type in the difference to be added here eg. 90.00M and this option can also be employed to include special fittings or valves with a known equivalent length rather than amending the database just for this one occasion.

The last option B stands for bars and permits you to add a special fitting or valve as a constant pressure drop eg. 0.50B. The default is 0.00M which doesn't do anything.

The following screen shot shows how the Edit screen changes when a pipe with a nozzle at its end is selected :-

Demo 1 edit a nozzle


Leave as 'None' if there is no nozzle at the end of this pipe. Select 'Usual' if this nozzle is the same "K" factor, minimum pressure and optional area in sq.m as given in the Job Data or 'Special' to type in a different "K" factor and/or minimum pressure and/or operating area as prompted by the next three questions. Again you do not have to type in the full number of decimal points and just press {tab} when done. Each nozzle can be exactly the same or different in varying rooms being protected and the associated 'hint' will show the minimum flow rate for guidance.


As you move between these items with {tab} or click on specific items with your mouse, the labels change to the corresponding value on the drawing (full size or zoomed in plan, elevation or isometric). A little square will be shown where the end of any pipe section meets a previously specified pipe to form a "loop" and FREEWATERMIST will adjust the calculations routine accordingly.

Pipe options - Add, Break, Copy, Delete, Edit or View :-

The first is Select option ... which will show a "arrow" cursor on the drawing that does not have any effect so as not to inadvertently change anything and is returned to after 'Job Data', 'Database', 'Calculate' or 'Results' for the same reason. To carry out the remaining 6 operations, select ...

Add another pipe

This option will add an additional pipe to the current drawing - just click the 'arrow with a square' cursor at or near the centre of the pipe (where the direction is) that you wish to connect to (the one that feeds it) and all the type, size, length etc. details will be copied to the new pipe highlighted in blue. These 'pipe data' list- and edit-boxes can now be selected, in turn, to revise them as needed, ie. different length, direction or size, which will be instantly shown on the drawing. There are no "OK" or "Cancel" buttons to click on before you can see this new pipe and please note, that such an arrangement also does not obscure the drawing showing the very pipe you are adding/changing, a common failure of older "paid-for" programs. The following shows a pipe added to the end of one of the branch lines in Demo 1 :-

Demo 1 add a nozzle

If you have added a pipe in the wrong place, then simply select 'Delete' to remove it and carry on in the right place, otherwise you will remain in 'Add' so can just click on the next pipe where another pipe and/or nozzle is required. Pipes not yet feeding any nozzles are shown in blue but will change to black as soon as one or more nozzles are drawn - this is just to highlight them as there will be no flow in them when you 'Calculate'.

Break a pipe in two

This is necessary if you want to insert another pipe at a location where there is no elbow / tee to connect to. Just follow the 'prompt' at the top of the drawing and click the 'two vertical lines' cursor at or near the centre of the appropriate pipe that you want to split into two (where the pipe numbers are shown). A pop-up message will confirm what has now changed (so click to dismiss it) to see the extra pipe highlighted and the option will revert to 'Edit' for the next action.

Demo 1 breaking a pipe

Copy group of pipes

This is most useful in duplicating one or more pipes already created to another part of the network. Again just follow the 'prompt' at the top of the drawing to click the 'cross' cursor at or near the centre of the size label of the first pipe of the group to be copied which it, and all the ones it supplies will then be shown in orange.

Demo 1 copy part 1

Now move your mouse cursor (an 'arrow' with some little squares under it) to the same or another pipe centre where these coloured pipes are to be copied to - as soon as you click the mouse, the drawing will change to show the existing and additional pipes / nozzles.

Demo 1 copy part 2

If you need to copy pipes but change their directions and/or slopes by a set angle (eg. 0 will do nothing but 90 will amend North facing pipes to East, eastwards ones to South etc) then just make sure the correct angle is selected in the 'Spin angle' list-box before the actual copying takes place. The last item is called "reverse" which will add 180 degrees to the pipe directions (so North becomes South, East becomes West etc) and change any positive pipe slopes to negative (so +6 will become -6) or already negative pipe slopes to positive (so -7 becomes +7) which may be useful in some pipe arrangements. Here I have copied the last group of nozzles to the end of the pipe we 'broke' earlier and rotated them by 180 degrees :-

Demo 1 copy part 2

When the copying is done, you will return to the 'Edit' option but if you have added some pipes in the wrong place, then simply select 'Delete' to remove them and try again. I also create a LastJobBeforeCopy backup file just in case the wrong copy pipes or angles are chosen.

Delete some pipes

This will remove one or more pipes / nozzles from the current drawing if no longer required or superfluous ones resulting from incorrect copying - just click the 'no entry' cursor at or near the centre of the pipe number of the pipe closest to the water supply that you want to erase (and all the others it supplies). The drawing will show these pipes in grey with a pop-up message asking for confirmation that you really want to delete those pipes (click on "Yes") or they are to left unchanged (click on "No") and you will return to the 'Edit' option - so if we did not want all those extra pipes we just copied, then they can be erased :-

Demo 1 after delete

Edit pipe data

Use this option to revise any of the various pipe data items described above - just follow the grey prompt to click the 'arrow with a ?' cursor at or near the pipe length label of the pipe to highlight it with the length selected in the same colour. Click on the list-boxes of other items to instantly change them for that same, highlighted pipe, again noting that the labels next to all the pipes on the drawing change to suit.

Demo 1 editing a pipe

You can then click on another pipe to view or revise the same or other information on that new pipe, without any further prompting or interruption.

Demo 1 edit any pipe

You do not have to click on any "OK" or "Cancel" buttons with this modern user interface and any changes you make are instantly reflected in the drawing on the right with the labels following suit so you can see that same data on all the other pipes / nozzles around the one you are concerned with. Note also that the information on the Edit part is exactly the same as the Add part as there is just no need for it to different!

View pipe info ...

As you move your mouse around the plans, elevations or isometric views, if you just hover over the centre of any pipe (usually where the size, length, direction etc. label is), a small yellow box will provide a summary of the data about that pipe / nozzle, including the calculations, if done, as :-

Demo 1 view

This is only really applicable to HD / 4K screens, as it is all a bit cramped on little laptops. Alternatively, if the pipe and its label are too close to the edge of the screen, then just choose another view or 'Zoom In'.


Throughout all the above five options, you always have to click the centre of the pipe in question and not sometimes the end, start or centre on the whim of previous programmers of older programs for this task. You can change the selection of option at any time (after clicking 'Add' you can change your mind and choose 'Edit' instead) and can likewise change the drawing view, zoom in or out or different labels or other options along the top or left hand sides of the FREEWATERMIST screen before, during or after a specific operation as you choose.

The best way to learn how to use these 6 options, is to play with my 'Demo 1' and 'Demo 2' examples as it doesn't matter if things go wrong as they are reset to my data every time you click on them.

You can also use "NotePad" or similar text editor to amend the job data file ending in .3WM if you prefer to make some changes, deletions or copying this way - you can also get a printout of it, if needs be and don't forget to keep backup copies on another PC or USB key in case your computer ever stops working.

Other features and topics :-

Velocity Pressure The equation in NFPA 750 is wrong - it should be 0.0049924 times the velocity squared and it can be used in high velocity mist systems to reduce the pressure and water quantity requirements. It only applies to intermediate nozzles along branch lines to give a smaller 'normal' pressure (which governs the flow) against the 'total' pressures at the pipe junctions / nozzles. It does not apply to the ends of pipes not feeding any other nozzles or those on loops / grids, so the 'Demo 1' example gets the same results whether you turn on velocity pressure or not in Q23 in the Job Data, as they are all 'end' nozzles. The longer the branch line, the more the reduction in flows and pressures (and perhaps pipe sizes) by including velocity pressure, so this is an essential feature of FREEWATERMIST for, say, over 4 nozzles per run of pipes as against other programs which omit this option. I have provided a short 'Basic' listing on my FREESHP webpage so you can see one could never calculate velocity pressure manually.

Accuracy The program balancies the pressures at all pipe junctions / nozzles to less than 0.001 bar as the 0.03 bar figure quoted in NFPA 750 just applies to manual calculations which nobody would ever do nowadays. However, you may find that some of the numbers given on the results presentation appear incorrect. For example, pipe 20 on the 'Demo 1' job shows the start pressure as 7.493, the friction loss as -0.127 and the end pressure as 7.367 bars. So where did the 0.001 difference come from? Well, looking into the program, the actual calculated values are 7.493364975, -0.126803310 and 7.366561665, which, if you get your calculator out, come to exactly zero or well under one millionth of a millibar. The 0.001 bar error is purely down to rounding the numbers to three decimal places for printing out and not to any inaccuracies or incorrect programming / mathematics in FREEWATERMIST. Likewise, if you add up the flows from the nozzles they may come to plus or minus 0.1 L/min of the source duty - again, just due to rounding. At least this shows that none of the figures has been 'fiddled' with and they are all exactly as calculated.

Windows Operating System You will note I have used Windows 7 for all the above screen-shots as I gather most of my users of all my other 18 FREE programs still rely on this. The program has been developed in 'Delphi' Pascal so will run on 32 or 64 bit versions of Windows XP, Vista, 7, 8, 8.1 or 10 (but not RT!) and the only Windows 10 PC I had did not survive the latest upgrade and no longer boots up! At one time, Microsoft sent umpteen Windows Updates that took 10-30 minutes to install and restart - now they force a multi-GB download of a completely new operating system which stops you using your own PC for several hours and then crashes it just when you didn't want a new operating system in the first place!

Some other points about FREEWATERMIST :-

Copyright 2015 by Alan Ashfield