Tankless Water Heater Dimensions: Wall Clearance
A tankless heater is a slim box, 7 to 18 inches wide and 11 to 28 inches tall, which is why people expect it to fit anywhere. It needs 12 inches of clearance all around for venting and service, and a gas unit needs 12 to 18 inches to combustibles around the vent. The wall it claims is much bigger than the box.
How big is a tankless water heater?#
A tankless water heater is a slim wall-mounted box: 14 to 18 inches wide for a gas unit, 14 to 17 for electric, and as little as 7 inches for a point-of-use heater under a sink. That compactness is the selling point and the trap. Around every one of them sits 12 inches of clearance for venting and service, and around a gas vent another 12 to 18 inches to anything combustible — so the wall a tankless heater occupies is considerably larger than its own dimensions. The table below is that difference.
Tankless water heater dimensions by configuration#
| Configuration | Width (in) | Height (in) | Depth (in) | Best for |
|---|---|---|---|---|
| Gas tankless water heater | 14–18 | 23–28 | 10–13 | whole-home hot water with a gas line |
| Electric tankless water heater | 14–17 | 17–22 | 4–8 | point-of-use or warm-climate whole-home |
| Point-of-use tankless heater | 7–12 | 11–15 | 3–5 | a single sink far from the main heater |
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What the wall has to give, beyond the box itself#
Each row is something the installation needs that no dimension in the table above will tell you.
| The requirement | What it is | Why the box size misleads |
|---|---|---|
| 12 in of clearance all around the unit | Venting and service access | A 14-inch-wide gas unit therefore claims a wall run far wider than 14 in — which is what people discover after the bracket is already up |
| 12–18 in to combustibles around the vent, gas only | A fire clearance, not a service one | It applies to whatever is near the vent, so a shelf, a cupboard or a joist inside that distance rules the position out |
| Studs, or a plywood backer | What it bolts to | It frees the floor a tank would occupy, but it needs real structure behind the plasterboard — a hollow wall is not a location |
| A larger gas line and correctly sized venting, gas only | Supply, not dimension | Both are sized to the firing rate, and it is why a gas tankless swap is rarely a like-for-like replacement for a tank |
| Depth of 3 to 13 in depending on class | The one dimension that behaves | An electric unit at 4 to 8 in deep and a point-of-use at 3 to 5 in genuinely do vanish into a cupboard; the gas class at 10 to 13 in does not |
Three classes are counted above — gas, electric and point-of-use — and their case sizes are the smallest in this corpus while their installed footprints are not. Clearances are venting and service requirements published per model, and a gas unit’s vent clearance is a fire figure rather than an access one.
Installation clearances for a tankless water heater#
- Wall clearance: 12 in in of clearance around a tankless water heater for the venting and for service access.
- Vent clearance: 12–18 in in a gas tankless water heater needs to combustibles around its concentric or twin-pipe vent.
- Wall mounting: A tankless water heater bolts to wall studs or a plywood backer, freeing the floor space a tank would occupy.
- Gas and vent: A gas tankless water heater needs a larger gas line and stainless or plastic venting sized to its firing rate.
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Will your tankless water heater fit? Clearances and door swing#
A tankless unit hangs on the wall, so it reclaims the floor a tank would eat, but it wants clear space around it for venting and service. Leave about 12 inches of clearance around the unit for access, and for a gas model plan 12 to 18 inches to combustibles around its concentric or twin-pipe vent, since it fires hard while running. Mount it to wall studs or a plywood backer rated for its weight. A gas tankless heater also needs a larger gas line than a tank unit and stainless or plastic venting sized to its firing rate, so that infrastructure has to be in place. An electric or point-of-use model is far shallower, just 3 to 8 inches deep, and skips the venting entirely. Confirm the wall can carry it and the vent or gas run is available.
Tankless water heater sizes by type: gas tankless water heater, electric tankless water heater, point-of-use tankless heater#
The three types scale from whole-home to a single tap. The gas tankless heater, 14 to 18 inches wide and 23 to 28 tall, delivers whole-home hot water but needs a gas line and venting. The electric tankless heater is slimmer at 4 to 8 inches deep and 17 to 22 tall, serving point-of-use or whole-home duty in a warm climate where the incoming water is not too cold. The point-of-use heater is the smallest, 7 to 12 inches wide and 11 to 15 tall, mounted right at a single sink far from the main heater to kill the wait for hot water. Match the type to your fuel and how much of the house it must serve.
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Tankless water heater dimensions: common questions#
How big is a tankless water heater?#
A tankless heater is 7 to 18 inches wide and 11 to 28 inches tall. A gas whole-home model is the largest; a point-of-use unit is the smallest.
How much wall space does a tankless water heater need?#
Leave about 12 inches of clearance around the unit for venting and service, and 12 to 18 inches to combustibles around a gas model's vent. Mount it to studs or a rated backer.
How deep is a tankless water heater on the wall?#
Depth runs 3 to 13 inches. A gas model is deepest at 10 to 13 inches, while an electric or point-of-use unit projects only 3 to 8 inches from the wall.
Is an electric tankless heater smaller than a gas one?#
Yes, mainly in depth. An electric unit is 4 to 8 inches deep versus 10 to 13 for a gas model, and it needs no venting, so it fits tighter spots.
How much clearance does a gas tankless heater need for venting?#
A gas tankless heater needs 12 to 18 inches to combustibles around its vent, plus properly sized stainless or plastic venting for its firing rate. That vent clearance is a hard requirement.
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