Tankless Water Heater Service in Hillcrest Estates, Frisco, TX

Gas sizing is the item that most often separates an honest quote from an optimistic one on housing of this age, and the method is not a secret. Every section of pipe is sized from the total load downstream of it, the developed length from the meter to the furthest appliance, and the permitted pressure drop. In a residential system at ordinary low pressure the working figure is generally a half-inch water column drop, and the capacity for each pipe size at each length comes off a published table.

The trap in older houses is the developed length. The measurement is not the straight-line distance from the meter to the appliance. It is the actual pipe route, plus an allowance for every elbow, tee and valve along it. A run that measures forty feet on a plan can easily be a developed length of sixty or seventy once the route around the framing and the fittings are counted, and that difference is often enough to move the required pipe size up a step.

Those are indicative figures for natural gas at a half-inch water column drop and they are there to show you the shape of the problem, not to size your house. Read the two rows for half-inch against a 199,000 BTU appliance and the conclusion is immediate: on any realistic run length, a half-inch branch cannot feed the unit on its own. Read the three-quarter inch row at eighty feet and you can see why the answer is sometimes to run a dedicated line from the meter rather than to upsize a long existing branch. Whether your house needs three-quarter or one inch depends on your measured length, your fitting count and what else is on that section.

This is worth explaining carefully because the honest answer is more nuanced than it is usually given. Water expands as it is heated. In an open system that expansion pushes harmlessly back into the street main. Where a pressure reducing valve or a backflow preventer sits at the meter, it acts as a check valve, the system becomes closed, and that expansion has nowhere to go except into a rise in system pressure.

Closed system

A domestic water system that cannot push water back toward the main, because a pressure reducing valve, backflow preventer or check valve sits between the house and the street. Most houses with a PRV are closed systems whether or not the owner knows it.

Where the honest nuance comes in is volume. A 50 gallon storage tank heating from 50 to 120 degrees expands by something over one per cent of its contents, which is roughly half a gallon with nowhere to go, and that is why expansion tanks became standard on tank installations. A tankless unit holds a fraction of a gallon, so the expansion it generates directly is small. That leads some people to conclude expansion control is unnecessary after a conversion, which is only sometimes right.

It stops being right as soon as there is a recirculation loop, a buffer tank or a long run of heated pipe holding volume, and it was never the whole story anyway, because thermal expansion is not the only source of pressure transients in a closed system. What we do on any conversion of this age is measure static pressure at a hose bib, check whether a PRV is present and functioning, and then make the expansion decision on the evidence rather than on habit. Code generally caps pressure at the fixtures at 80 psi, and a house sitting near or above that with a failing PRV has a problem the water heater did not cause and the water heater will get blamed for.

Most of what is written about tankless conversion is written by people selling tankless conversion, so it is worth setting out where the case is genuinely weaker. On a modest-fixture house with older infrastructure, the conversion carries costs that a newer house does not: gas branch upsizing, complete re-venting because an existing atmospheric chase cannot be reused by either type of tankless unit, and a condensate route that did not previously exist.

Against that, the efficiency gain on a modest household is proportionally smaller in absolute terms, simply because a smaller household uses less hot water and therefore saves less of it. A high-efficiency appliance saves a percentage, and a percentage of a small number is a small number. The genuinely strong arguments for converting here are the ones that are not about the gas bill: no stored reservoir to fail, no recovery limit, floor space returned, and an appliance with a service life that can run two to three times that of a storage tank if it is descaled.

That fifth row is the one we say out loud more often than people expect. A sound tank that is doing its job does not need replacing because tankless is better in the abstract. Draining a few gallons of sediment off the bottom once a year and leaving it alone is a perfectly respectable plan, and it costs nothing.

Competing bids on a conversion frequently differ by thousands, and the spread is almost never the same work at different prices. It is different work. The typical installed range of $2,500 to $6,500 exists precisely because the scope varies this much between houses and between quotes. The way to compare them is to force each one onto the same line items.

• Does it name the model and BTU input, or just say tankless? A number is checkable, a category is not
• Does it state condensing or non-condensing, and does the vent material named match that category?
• Is gas branch work included, excluded, or left as to be determined on the day?
• Is a load calculation mentioned at all, or is the existing branch simply assumed adequate?
• Is the permit and inspection fee a line item, typically $100 to $300 here, or is it absent?
• Are isolation valves with hose ports included, or an optional extra?
• Is condensate handling specified, including a neutralizer and a named drain destination?
• Is expansion control addressed, and is static pressure being measured to decide it?
• Is drywall or finish repair included where a vent penetrates finished space?
• Is disposal of the old tank included?

Score three quotes against that list and the cheap one usually stops being cheap. The commonest omissions are the gas branch and the venting, which are exactly the two items an older house is most likely to need, and both are difficult to argue about once the old tank is already on the driveway. A quote that has been written after somebody actually looked at the gas run and the proposed vent route will be higher than one written over the phone, and it will also be the price you end up paying.