Indoor Tankless Water Heater Installation in Frisco, TX

Two different sets of dimensions govern where an indoor unit can hang, and homeowners almost always look at the wrong one. The listed clearance to combustibles is a fire-safety number printed on the data plate, and on a sealed-combustion unit it is often remarkably small — zero to one inch at the sides and back is common, because the cabinet is insulated and the exhaust never touches framing. The service clearance is a completely separate number, it is much larger, and nothing in the fire code enforces it.

Service clearance

The space a technician needs to open the front panel, withdraw the burner assembly, reach the isolation valves and connect a flush pump. Manufacturers publish it, typically around 24 inches in front and 12 inches above and below, but it is a serviceability requirement rather than a safety one. An installation that meets every listed clearance and none of the service clearances will pass inspection and then be miserable to descale for the next twenty years.

The weight matters more than the number suggests. Fifty to eighty-five pounds is not heavy in isolation, but it is hanging off a bracket in shear, with rigid gas and water piping attached, and in a Frisco garage it is very often on an exterior wall built with a single layer of drywall over studs at sixteen inches on centre. If the bracket lands between studs, it needs solid blocking let into the bay, not drywall anchors. We add blocking as a matter of course rather than hunting for a stud that happens to be in the right place, because the alternative is a unit that slowly works loose and puts strain on the gas connection.

A sealed-combustion unit moves its own exhaust with a fan, and that fan has a finite amount of push. The manufacturer converts that into a single allowance — the maximum vent length — and every fitting in the run consumes part of it. This is the arithmetic that decides whether an interior closet on the far side of the house is a real option or a fantasy, and it is done before anything is ordered rather than discovered halfway up a chase.

Equivalent length

The straight-pipe length that produces the same resistance to flow as a given fitting. A 90 degree elbow does not cost you an elbow, it costs you several feet of your budget. Total equivalent length is the sum of the straight runs plus the equivalent length of every fitting and the termination, and it must come in under the published maximum for the vent diameter fitted.

The practical consequence is that vent diameter is a design decision, not a default. Most residential units accept two-inch or three-inch pipe, and going up a size can roughly double the distance the unit can sit from its termination. The larger pipe costs a little more per foot and needs a slightly bigger hole through the top plate, and it is routinely the difference between a closet installation that works and one that has to be abandoned for a garage wall. Where the run has genuine height to climb — a ground-floor closet venting up through a two-storey Frisco elevation to a roof — we specify the larger diameter as a matter of course.

The other item that quietly eats the budget is the choice between a two-pipe system and a concentric one. Concentric venting carries intake and exhaust in a single pipe-within-a-pipe and needs only one penetration, which is much tidier through a finished ceiling and much easier to flash on a roof. It also has a higher fitting resistance and its own equivalent length charge at the terminal. On a short garage run that is irrelevant. On a long interior run it is sometimes the reason a job needs three-inch pipe.

The garage wall is the default recommendation in Frisco for good reasons — short vent run, easy service, no water above a finished ceiling — but it is also the location with the most code detail attached, and much of what homeowners have read about it is out of date.

The best-known rule is the eighteen-inch elevation requirement, which historically required an appliance in a garage to have any ignition source at least eighteen inches above the floor, on the reasoning that petrol vapour is heavier than air and pools low. Recent code cycles relaxed that for appliances specifically listed for garage installation, and most current tankless units carry that listing. Frisco enforces a particular adopted edition, and which edition is in force is a question with a definite answer rather than a matter of opinion. We confirm it at permit rather than assuming, because it is a cheap thing to check and an expensive thing to be wrong about at inspection.

• Physical damage protection where a vehicle could strike the unit — a bollard or a solid barrier, not a painted line
• A weather-resistant, GFCI-protected receptacle for the unit's controls, since a garage is a required GFCI location
• Mounting high enough that the isolation valves and condensate trap are not in the path of a car door
• Vent termination clear of the overhead door opening and of any gravity intake serving the house
• A condensate route that does not simply discharge onto the garage slab, where it will etch the concrete over time

The one genuine disadvantage of a garage is temperature. A Frisco garage is outside the conditioned envelope and usually uninsulated on at least one wall, so on a January morning it can sit only a few degrees above outdoor air. The unit's own freeze protection handles that comfortably while it has power, but the water lines running to it are in the same cold space and they are not protected by the cabinet heaters. Insulating those runs is a small line item and it is the difference between a nuisance and a burst pipe during a hard freeze with the grid down.

Manufacturers publish an ambient operating range for the appliance itself, distinct from anything to do with the water. It is commonly around freezing at the bottom and 120 degrees F at the top, with a handful of models rated higher. A Frisco attic in July, at the 130 to 150 degrees F that is normal here for an unconditioned roof space, is outside that range. The unit will usually still run, because the controls are conservative and the failure is gradual rather than immediate, but electrolytic capacitors and display modules age on a curve that is steeply temperature-dependent, and the practical result is a control board with a shorter life than the same board in a garage.

The mitigation is sealed combustion, and the benefit is larger than it sounds. A unit drawing combustion air from the attic is pulling 130 degree air loaded with cellulose or fibreglass dust across its burner and fan every time it fires. A two-pipe direct-vent installation draws that air from outdoors instead, which keeps the dust out of the burner and, on a hot afternoon, actually feeds it cooler air than the space it is sitting in.

There is one respect in which the attic is genuinely working in your favour, and it is worth understanding because it explains why a tankless unit feels stronger in August than in January. Output is set by the required temperature rise. In summer, Frisco inlet water arrives closer to 75 or 80 degrees F rather than the 50 to 55 degrees F of January, so a 105 degree shower needs a rise of 25 to 30 degrees instead of 55. That is roughly double the flow from the identical appliance. Nothing about the unit changed; the water it was given did.

A drain pan is a passive device. It catches water and, if it has been piped somewhere sensible, it puts that water where somebody will eventually see it. What it does not do is stop the leak, and the failure mode people worry about in a Frisco attic is not a slow weep from a fitting. It is a supply connection or a burst line running at full house pressure into insulation above a bedroom ceiling, which a one-and-a-half inch pan drain cannot keep up with and nobody notices until the ceiling changes colour.

The answer is an active system, and it has become cheap enough that we recommend it on every attic installation and most closet installations above finished space. A sensor sits in the pan and, where the geometry allows, a second sits on the floor of the closet or the attic decking. When either detects water it closes a motorised ball valve on the cold feed to the unit and sounds an alarm. The whole assembly is a few hundred pounds of parts and it fits in the time it takes to make up the water connections, which is why doing it during the installation costs a fraction of what it costs as a separate visit.

1. 1

   Pan sized to the appliance, not to the old tank

   A pan sized for a 50 gallon tank is far larger than the unit needs, which is fine, but the pan must sit under the whole footprint including the condensate trap and the isolation valves, since those are where a slow leak actually starts.

2. 2

   Secondary drain terminating somewhere conspicuous

   Above a window or a garage door, not into the attic insulation and not into a soffit where the water runs down inside the wall. The point of the drain is to be embarrassing.

3. 3

   Sensor in the pan and a motorised shutoff on the cold feed

   This is what converts a pan from a container into a control. It stops the supply rather than merely routing it, which is the difference between a wet patch and a replaced ceiling.

4. 4

   Condensate overflow considered separately

   On a condensing unit the condensate line is a second thing that can block. A saturated neutraliser cartridge or a plugged trap backs up into the cabinet, and on some models that produces a fault code long before it produces visible water.

5. 5

   Test it, then test it again at handover

   A sensor nobody has ever wetted is an assumption. We put water in the pan, watch the valve close and watch it stay closed, and then show you how to reopen it so an alarm at midnight is not a call-out.

The noise question comes up late, usually after the location has been chosen, and it is easier to solve before the bracket goes on the wall. A gas tankless unit makes three distinct sounds and they behave differently in a building.

• A click at ignition, brief and sharp, audible mainly at night in a quiet house
• A steady blower note for as long as the burner runs, broadly comparable to a bathroom extract fan
• A post-purge, where the fan continues for a short period after the tap closes to clear the exchanger

The blower note is airborne and it attenuates well through a closed door and an insulated wall. The problem sound is structure-borne: fan vibration transmitted through the mounting bracket into the framing, which then radiates from the drywall on the far side. That is why a unit on the shared wall of an under-stair closet can be audible in a bedroom above while the same unit in a garage is inaudible six feet away. Resilient washers at the bracket and a short flexible section on the water connections take most of it out, and choosing a bay that does not back directly onto a bed head takes out the rest.

The third source is the termination itself. Exhaust leaves under fan pressure and it makes a low rush at the outlet. Terminating three feet from a bedroom window that is open in April is a solvable problem in the design stage and an expensive one afterwards, since moving a termination means moving the pipe, the penetration and the patching. We look at what is on the other side of every candidate wall before recommending one.