Radiant heat layout

PEX loops laid out over a slab, a manifold to a zone, with the material list, a heat load if you want one, and a submittal to hand in and to lay the tube from.

Open it from Shop > Radiant heat layout... or type /radiant (/pex and /hydronic do the same). Select the floor first. Nothing goes on the drawing until you press Draw the layout, and Cancel or Esc leaves the drawing as it was. The radiant tools are an add-on: the first time, they ask for the license number that came with it, and once it is accepted they do not ask again.

What it does

You give it the floor and where each manifold hangs. It lays the tube in rows at the spacing you ask for, parallel to the manifold's wall, in loops that go out and come back on neighboring rows. Every loop is a round trip from the manifold and back, and its length - both leads included, plus 6 ft for the climb up the wall to the manifold and the tube fanned out onto the grid there - is kept under the longest loop you allow. No loop crosses another, and the tube stays 6" off every wall and obstacle.

It does not lay one layout and stop. It searches: it tries many layouts for each zone and keeps the best ones, ranked by how much of the floor they reach, how close the loop lengths come to each other, and how easy they are to lay. You pick the one to build, or take the best.

Before you start

1. Draw the floor. Any closed shape works - a rectangle, an L, a room with a curved wall.
2. Split it into zones by drawing lines across it. Every face is a zone, with a manifold of its own. A barn drawn as one big rectangle with lines across it is four faces, so four zones.
3. Cut out what the tube must stay out of - a column, a shaft, a chase - so it is a hole in the floor's face. The tube is routed around it.
4. Select the floor. Clicking the faces, a drag, or Ctrl+A all work: only faces are used, and the lines that come along are ignored.
5. Open the wizard.

A face that is the same shape as a hole in another selected face is left out on its own - it is the column drawn inside the slab, not a zone. With nothing selected, the wizard does not open and says to select the floor first.

The settings

The column on the left. A bare number is inches for the spacing and feet for a loop - 9 is 9", 300 is 300 ft. A foot or inch mark, or a metric size, is read as written.

Setting	What it is
Tube	3/8", 1/2", 5/8" or 3/4" PEX.
Spacing, on center	How far apart the rows are. 9" to start.
Longest loop	The most tube in one loop, manifold and back. Blank is the tube's own: 200 ft for 3/8", 300 ft for 1/2", 400 ft for 5/8", 500 ft for 3/4".
Most loops a manifold	2 to 64, 12 to start - most makers stop at twelve. A zone that wants more is yours to split in two; the wizard does not put a second manifold in it.
Search until ... % of the floor covered, and the loops within ... % of each other	The goals. A search keeps going until its best layout meets both, or you stop it. 0 is no goal. 97% and 10% to start.
Loops in hooked pairs, to even them	Two neighboring loops share their rows, split by one hook at the far wall. Ticked, the search tries these alongside plain layouts.
Show the labels	The loop and manifold notes on the drawing. Unticked, they are still built, but put away - /show labels brings them back, /hide labels puts them away again.
Job name	Goes on the submittal and names the zones' groups - Smith residence.

The settings are remembered from one job to the next; the job name is remembered for the floor it was given to. Changing the tube, the spacing, the longest loop or the most loops a manifold throws away every zone's layout, since the tube can no longer go where it went: search again.

The slab is not asked about. The wizard takes a 4" concrete slab, the tube centered in the pour, R-15 under it, and says so on the material list and the submittal.

Zones and manifolds

The plan in the middle shows the floor north up, with a compass in the corner. Each zone is outlined, holes are shaded gray, and each manifold is a small numbered box - the one you are working on is yellow. Once a zone is searched, every loop is drawn in its own color, so you can follow one run by eye.

When the wizard opens, it puts a manifold in every zone, tight to a wall, toward the middle of all the zones - where the boiler most likely is. Suggest manifolds puts them all back there.

Tabs

Under the plan there is a tab for each zone, and All zones when there is more than one. Click a zone on the plan and its tab comes up. A zone's tab has:

• Name - Kitchen, barn east bay. It shows on the tab, the plan, the material list, the submittal and the zone's group on the drawing, and is remembered for that floor.
• Keep the manifold where I put it - see below.
• A line saying where the manifold is and how the zone stands: not searched yet, or the size of manifold its layout takes, how many layouts were searched in how long, and how installer friendly it is. Before you search, it warns you when your coverage goal is out of reach for this tube, or when the zone wants more loops than one manifold takes.
• Search this zone, Clear it (throws away its layout), and Not a zone.
• Layouts found, best first - see picking a layout.
• Material list - this zone's. On the All zones tab, every zone's together, with the totals.

Moving and turning a manifold

• Drag a manifold's box to move it. It stays inside its own zone. While you drag it, and while its zone is open, it shows its distance from its middle to the wall each way, and it lands whole inches from the nearer walls, so you can put it on a mark you measured.
• Out in the floor, away from every wall, its loops leave from its front and its back. On a wall, from its front.
• Drag it within about a foot and a half of a straight wall and it goes tight to that wall, turned to lie along it - and keeps that heading when you drag it away again. That is the quick way to turn one and then move it out into the floor.
• Right-click it for Rotate manifold 90 degrees, or Square the manifold: long side east - west, north - south, at 45 degrees, or at 135 degrees.

Moving or turning a manifold throws away that zone's layout. The other zones keep theirs.

Keep the manifold where I put it

When a search is stuck, as a last resort it may slide the manifold along its wall a few feet, and the material list says how far it moved it. Tick Keep the manifold where I put it when the spot you picked is the only place it can hang. It is remembered for that zone.

Not a zone, and bringing it back

A closed shape in the selection that is not floor to heat - a chase, a column against a wall - can be left out. Pick its tab and press Not a zone, or right-click it on the plan for Zone N is not a zone - leave it bare. It turns gray on the plan, gets no tube, and stays out the next time you open this floor. The last zone cannot be left out.

To bring them back, right-click the plan: Bring back the shapes left out. Every one left out comes back as a zone, with its manifold where Suggest would put it.

The plan's right-click menu

Right-click a manifold, or inside a zone, and the menu acts on that zone:

• Search zone N, and Search all zones.
• Zone N is not a zone - leave it bare, and Bring back the shapes left out.
• Rotate manifold 90 degrees, and Square the manifold.
• Clear zone N, and Clear all zones - their layouts, not the zones.

Searching

A search takes seconds a zone on a real floor, longer on a big one, so nothing is searched until you ask. Press Search this zone on its tab, Search all zones, or use the plan's right-click menu. A zone not searched shows no tube, and Draw the layout stays off until every zone has been searched.

What a search does

1. It lays a set of layouts first: the rows both ways, the first loops given more or less of the longest loop, different distances for the tube to fan out from the manifold. With no goals, that is the whole search.
2. With goals, it keeps going: more layouts tried at random - loops of different lengths, lanes nudged, rows turned - until the best one meets the goals, or you stop it, or it reaches its give-up time.
3. Along the way, and more as it gets stuck, it may even up the rows at the far wall by closing them up an inch or so, lay loops with hooks at the far wall, and - unless you told it not to - slide the manifold along its wall. The material list and the submittal say when any of this was done.

A layout only meets the goals when it covers enough, its loops are within the spread you gave, no join runs through an obstacle, it needs no more loops than a manifold takes, and it is friendly enough to lay (below). Each search starts from a new random point, so searching a zone again can find a different layout.

When a coverage goal is more than the tube can reach - say twelve loops of 300 ft at 9" on a 3,000 sq ft zone - the zone's tab says so before you search, with what to change: a wider spacing, a longer loop, more loops a manifold, or the zone split. The search then works toward what the tube can reach.

The search window

While it searches, a window stays up over the wizard. It shows which zone it is on (and which of how many), a bar, the layouts laid a second, and the best so far - how much it covers, how close its loops come, and how many loops. Everything in it can be changed while it runs:

Control	What it does
Goals	The same two goals as the wizard's. Change them here and the search works to the new goals from the next layout. What you leave here is the wizard's goals afterward.
Give up after	Never, or 1, 5, 15 or 30 minutes, or 1 hour, a zone. Past it, the zone keeps the best it found and the next zone starts.
Less friendly layouts too, to meet the goals	Off, the search keeps to layouts an installer lays easily - 85 of 100 or better. Tick it to let it lay harder loops when that is the only way to meet the goals.
Hooks at the far wall	A loop run on over its neighbor's first two rows, to even the loop lengths - four bends. Untick it and hooks are never tried.
Found so far, best first	The layouts it has kept. Click one to see it drawn beside the list and to keep it as the zone's layout; double-click one to stop and keep it.
Stop - keep the best	Ends this zone with the best it has, and goes on to the next zone.
Stop all	The same, and searches no more zones.

Give up after, less friendly and hooks are remembered for next time. While the window is up, the wizard cannot be changed or closed.

Picking a layout

A search keeps up to 24 layouts a zone. Each line in the list, best first, reads:

• how much of the floor it covers, percent;
• how far apart its loops are - how much shorter the shortest is than the longest, percent and then feet;
• how many loops, and how many bends;
• how installer friendly it is, of 100;
• ok when it meets the goals.

Click a line in the zone's Layouts found list and that is the layout the zone shows and will build. The material list says which of how many it is.

Installer friendly

Each loop is scored out of 100 for the person laying it. A plain serpentine block, set out from two measurements, is 100. A loop loses points for every measurement past two it takes to set out - where its rows stop short of a wall, and where its lead runs - for bends past a plain serpentine's, and for reaching out past its own block of floor into the others'. A layout's score is the average of its loops'.

The gauges and the material list

Two bars over the plan, over the zones searched so far:

• Coverage - how much of the floor the tube actually reaches.
• Evenness - how close the loop lengths come, in the zone where they are furthest apart, as a percent and in feet.

Green is good, amber is part way, red is poor.

The material list for a zone gives the tube and spacing, the floor area, the loops, the manifold's size and about how much wall it takes, every loop's length, and then:

• total tube, and for each roll size how many rolls it takes and what is left on them;
• ties or staples, one every 15";
• how many bends, and how much of the tube runs in long straights;
• how far out from the manifold every tube is on the grid;
• whether the turn at the end of each row - the spacing - is tighter than the tube bends, and which PEX (A, or B and C) can make it;
• any join that runs through an obstacle - route those by hand;
• floor not reached, the slab assumed, how friendly it is to lay, and the search's record;
• SHORT OF THE GOALS, OUT OF REACH or MORE LOOPS THAN ... A MANIFOLD IS SET TO TAKE where that is so, with what to change.

The line in red just above Draw the layout says what stops the layout: a size that does not read, or a zone with no layout.

The heat load

Heat load... opens a window of its own. It is optional: a layout builds without it, and the submittal only carries a heat load once you use one. Once you do, the button reads Heat load - in.

It is a simplified heat loss - walls, glass, doors, ceiling, the slab's edge and the air that leaks in - at the code U-values for the climate zone, worked out as you type. The answers are remembered for that floor.

The building

Setting	What it is
Outdoor design	The 99% winter low for the town, degrees F - ask the supplier or look it up (ASHRAE).
Indoor	68 F to start.
Climate zone	The IECC climate zone, 1 to 8. ? opens the Department of Energy's guide in your browser, which lists every county's zone.
Glycol	Percent propylene glycol in the water. It carries less heat and is thicker, so the flow and head go up.
Altitude	Feet. Past 2,000 ft the boiler is derated 4% for every 1,000.
The boiler makes the hot water too	A combination boiler. Tick it and give the number of bathrooms; the boiler is sized for whichever is larger, the heating or the hot water.

The outside walls

The plan shows the zones. Click a wall to change it, round and round: blue is an outside wall, orange a wall to a space not heated - a garage - and gray an inside wall. A wall two zones share is always inside. To start, every wall no other zone shares is taken as outside. Click inside a zone, or pick it from the list, to fill in that zone.

Each zone

Setting	Choices
What it is	Slab on grade; slab over a heated space; joists with plates, over a crawlspace; snow melt.
Above it	Attic, insulated to code; roof, insulated to code; heated space; bare metal roof.
Outside walls	Up to code; older - R-11; bare metal.
Slab insulation	Under it all, to code; R-10 at the edge only; none. Slab on grade only.
Floor covering	Bare concrete; tile or stone; vinyl or laminate; wood; carpet and pad.
Air tightness	Tight - new, sealed; average; leaky - old, drafty.
Snow melt	Residential walks and drives; commercial; must stay clear - ramps, hospitals. Snow melt only.
Header to boiler	How far the pipe runs from this zone's manifold to the boiler, one way: up to 20 ft, 20 to 50, 50 to 75, 75 to 100, 100 to 150.
Ceiling height	Feet.
Windows	Square feet of glass in the zone's outside walls, all told.
Overhead doors	Square feet of them.

A snow melt zone asks only for its class; it is a rate over the surface, not a loss, and is kept apart from the heating load.

What it works out

For the zone you are on:

• the loss by where it goes - walls, windows, doors, ceiling, slab edge, floor down, air - and the total in BTU/hr;
• what the floor has to give, BTU/hr a square foot, and its surface temperature. Past what a floor gives at 85 F it says SHORT, and how much has to come from other heat;
• the water: supply and return temperatures, and the zone's GPM;
• the loop that needs the most head, its GPM and feet of head - once the zone has been searched;
• the copper pipe size from the header to the boiler;
• the pump: GPM at feet of head.

And the boiler for all the zones: the heating, 5% for the piping, the hot water if it makes it, the altitude derate, the rated output it needs at least, the input at about 95% efficiency, how far down it should modulate (the smallest zone), and the snow melt, alone and with one boiler doing both.

Use it puts the heat load in the submittal. Leave the heat load out takes it out. Cancel keeps what was there before.

The submittal

Export the submittal... saves the job as a PDF - on letter paper, or A4 for a metric drawing - or as plain text if you pick a .txt file. It is named for the job to start with. Preview the PDF writes the same PDF where nothing is kept and opens it in your PDF reader, so you can look it over first.

It covers the zones searched so far; a zone not searched says it has no layout. In order:

• The job - the slab and its overall size, the tube and spacing, the zones and manifolds, the loops, the floor, the tube laid, and ties.
• Material list - the tube, the manifolds by size with the wall each takes, ties or staples, and the insulation under the slab.
• Tube by the roll - for each size the tube is sold in that a loop fits on, how many rolls it takes and what is left on each. A loop comes off one roll in one piece, the loops laid in order, each off the first roll that still has enough on it. A roll too short for some of the loops names them.
• Zones - a line each: floor, loops, manifold, wall space and tube.
• The plan of every zone, north up, with the slab's overall length and width, every manifold dimensioned, and a scale bar. A manifold is dimensioned from the nearer wall each way, along its wall and out from it, to its middle - not from a wall it is against.
• A page for each zone - its plan with the manifold dimensioned, a table of its loops (length, color, and which roll each comes off with what is left on it after), what it takes, the heat, water and pump when there is a heat load, anything out of the ordinary (the manifold moved, rows closed up, a tight turn, short of the goals, too many loops), and how it was found.
• A setting-out sheet for every loop, a loop to a page for the binder: the loop by itself in its color with the others faint, what should be left on the roll once it is down for each roll size (measure the tail to check the loop went in as drawn), the dimensions to mark it out from the walls - to the first row, across the rows, to where the rows turn, to the far wall, each lead from its nearest wall - the manifold's dimensions too, a warning when it takes more than two measurements, a scale bar, and an installer checklist: rows marked, tube laid and tied, what was left on the roll, both ends tagged, supply and return connected, pressure tested, flow set (to the design GPM when there is a heat load), then laid by, date and checked by. Every loop of a zone is at the same scale. The loops are numbered left to right along the manifold, standing in front of it, so the sheets go up the manifold in order.
• Heat load, water and the boiler, when one is used - the design conditions, the boiler, a line for each zone, where the loss goes, what was asked, anything to watch (a floor short of its load, water over 120 F for a slab, a pump past 25 ft of head, snow melt without glycol), how it was worked out, and every table value used, with its source.
• Design record - the longest loop allowed, the goals, how much of the floor the tube reaches, installer friendly, a line for each zone (reached, loops within, bends, easy, goals met), and for each zone, when it was searched, how many layouts in how long, what happened on the way (stopped by hand, gave up, picked by hand, goals met at which layout), and the layouts it kept, the chosen one marked.
• How this layout was made - the rules the layout keeps, in a few lines.

Every sheet has a title block: the job, the date, the program's version, and sheet N of M. A scale bar reads true even printed "fit to page", where a stated scale would not.

Building it

Draw the layout puts the layout on the drawing exactly where the floor is - nothing to place afterward - and leaves what it built selected. It builds the layouts the wizard showed; it does not search again. For each zone:

• A group named for the job (or Radiant), the zone and its name, and what was laid - the tube, the spacing, the number of loops and the total length: 1/2" PEX at 9" o.c. - 11 loops and so on.
• Inside it, every loop a group of its own, named Z1 L3 with its length. Click one and you have the whole run from port to port; the entity panel gives its length. Each loop is drawn in its own color, as on the wizard's plan.
• The manifold as a box, turned the way it hangs, in a group of its own - Z1 manifold - 11 loops.
• A labels group: each loop's name and length, no tube - obstacle on every hole, and a note by the manifold with the zone's summary. /hide labels and /show labels put them away and back.

The runs are reference lines, like a dimension's own line: they draw in full but never close faces with the floor. Undo takes the whole build back in one step.

After it is built

The drawing keeps the whole job in the zones' groups - the settings, every zone and manifold, the names, the heat load and each zone's layout. Click a zone's group and right-click it for:

• Open in the Radiant Wizard... - the wizard, titled as it was built, on the job just as it was: its zones, manifolds, settings, names and layouts, searched already. Change what you like. Draw the layout puts the new layout in place of every one of the job's old zone groups, in one undo step; Cancel leaves the drawing alone. A zone whose group was erased comes back not searched.
• Print the Submittal Again... - the submittal as it was built, PDF or text, with no search and no wizard.

Only the layout each zone built keeps its loop paths. The other layouts its search kept are kept as a record - how much they covered, their bends and lengths - for the design record. Pick one of those in a reopened wizard and it says Only the built layout was kept - search again for the rest.

Layouts built before 28 September 2026 did not keep their job, so these two items do not show for them. Select the floor and run the wizard again.

Limits

• It is not an engineered design. The layout is geometry at the spacing and lengths you gave it. The heat load is a simplified estimate for choosing the boiler, the pumps and the pipe - not a Manual J, and not a room-by-room load calculation where a permit asks for one. Check the design against the tube and manifold maker's instructions and the code where the job is.
• The search is bounded. It does not promise to reach every corner of an odd floor; the material list says how much was not reached.
• The slab is not asked about: 4" thick, tube centered, R-15 under it.
• One manifold to a zone. A zone that wants more loops than a manifold takes is for you to split.

Where the numbers come from

Number	Value	Where from
Longest loop	3/8" 200 ft, 1/2" 300 ft, 5/8" 400 ft, 3/4" 500 ft	Tubing makers' install manuals and Radiant Professionals Alliance guidance - the low end of each quoted range
Tightest bend	8 times the tube's outside diameter for PEX-B and PEX-C, 6 times for PEX-A	The same
Spacing	6" to 12" covers most slabs; 9" the everyday default	The same
Under the slab	R-15 at least	The same
Tube off walls and obstacles	6"	Trade practice
Manifold sizes	2 to 12 loops	What the makers offer
Manifold wall space	2" between connections, supply and return side by side, and 12" for the valves and end caps	A rule of thumb
Rolls	100, 300, 500 and 1,000 ft, and 400 ft for 3/8" and 5/8"	What oxygen barrier PEX is commonly sold in (Uponor hePEX, Sioux Chief, BOW, the box stores)
Ties or staples	One every 15"	An estimate
Heat load tables	U-values, slab edge F-factors, air changes, floor output, pipe sizing	IECC 2021, ASHRAE Fundamentals and HVAC Applications, ASHRAE 90.1, EN 1264, ASTM F876 - listed value by value in the submittal