Tankless Water Heater Service in Edgestone at Legacy, Frisco, TX

Hardness is usually described in grains per gallon and then left as an abstraction, which is why annual descaling sounds like an upsell rather than arithmetic. Convert it and the picture changes. One grain is 64.8 milligrams. Water at 10 grains per gallon is therefore carrying about 0.65 grams of dissolved mineral in every gallon, most of it calcium and magnesium carbonate.

A large household in a plan of this size will move somewhere in the region of twenty to twenty-five thousand gallons of hot water in a year. At 0.65 grams a gallon that is thirteen to sixteen kilograms of dissolved mineral passing across the heat exchanger annually. The overwhelming majority of it stays in solution and leaves down the drain. But calcium carbonate becomes less soluble as temperature rises, and the exchanger wall is the hottest surface the water touches, so a small percentage comes out of solution precisely there. Even one or two per cent deposition is a few hundred grams a year building up inside passages that are deliberately narrow.

The sequence of symptoms is predictable and none of them look like scale. Outlet temperature starts hunting, because the restriction upsets the flow-to-firing-rate relationship the controller assumes. Then usable flow drops, because deposit is an insulator between burner and water. Then the unit begins tripping its high limit, because the metal at the exchanger wall is now far hotter than the water leaving it. A household with a soaking tub and multiple showers notices the second stage before the display ever shows anything.

Two units plumbed together are not simply double the capacity. They are a controlled system, and the control logic is where most of the value and most of the misconfiguration lives.

Cascade control

A communication link between two or more units that lets them behave as one appliance. It decides which unit fires first, at what demand the second joins, and how run hours are shared between them. Set correctly, both units age at the same rate and neither runs at an inefficient part of its modulation range.

Consider what happens at a small draw, such as a single hand basin at 0.8 gallons per minute. A single 199,000 BTU unit modulates down, but every unit has a minimum firing rate below which it cannot go, and at very low draws it will cycle rather than modulate. With a cascade the correct behaviour is that only the lead unit responds at all, and the second stays off until demand crosses a threshold. Where the configuration is wrong, both fire on every draw, both short-cycle, and both accumulate ignition counts at twice the necessary rate.

The rotation setting matters most over the long run. If one unit has been taking nearly all the duty since the house was finished, it is effectively several years older than its twin and will need attention several years sooner. Correcting the rotation does not undo that, but it stops the gap widening, and it means both units can be descaled on the same visit and left in genuinely comparable condition.

A large plan needs recirculation, and a recirculation loop left running around the clock is one of the quietest ways to spend money in a house. The physics is unglamorous. Any pipe carrying 120 degree water through cooler surroundings loses heat to those surroundings continuously, and the loop pump exists to keep replacing that heat.

The order of magnitude is easy to establish. Uninsulated three-quarter inch copper at 120 degrees loses heat to a surrounding space at a rate of roughly twenty to thirty BTU per hour for every foot of pipe, and considerably more where the pipe passes through an unconditioned attic in January. A long loop in a large house, running continuously, is therefore a standing burn of a few thousand BTU an hour, every hour, whether or not anybody is awake. Over a year that is a number in the hundreds of therms, and the burner has to produce every one of them.

1. 1

   Insulate the loop, all of it

   Insulation on the return as well as the supply is the single highest-return correction, and it is often the part a builder finished only in the accessible sections.

2. 2

   Replace continuous running with a schedule

   Most households have two clear hot water windows. Running the pump for those windows rather than twenty-four hours cuts the standing loss by most of it.

3. 3

   Better still, trigger it on demand

   A button or occupancy sensor at the far bathroom runs the pump only when someone is actually there. It delivers hot water within about thirty seconds and then stops.

4. 4

   Check the loop is not scaling the exchanger faster

   Continuous recirculation puts many times more water through the heat exchanger than the household actually uses. At 8 to 11 grains per gallon that directly accelerates deposition, which is a second and less obvious cost of leaving the pump on.

When the equipment came with the house, the homeowner has no baseline for what service should involve or cost, which makes this the easiest situation in which to be sold something unnecessary. The following is what a genuine annual service on a condensing tankless unit consists of, so you can compare any quote against it line by line.