Hot Water That Takes Forever To Arrive

A tenant runs the shower for ninety seconds before it warms up. The hot water unit is working perfectly.

The wait is the cold water sitting in the pipe, and it has to come out before the hot arrives.

Why the wait happens

Every litre in the pipe between the unit and the tap has to be pushed out first.

Which means the wait depends on two things: how long the run is, and how wide the pipe is. A long run in oversized pipe holds a lot of water, and the tenant pays for all of it going down the drain.

In an apartment with a central hot water plant and a long horizontal run to the far unit, the wait can be two minutes. In a house with the unit on the far side from the bathroom, it is much the same problem.

What makes it worse

Oversized pipe. A 20mm line where 15mm would do holds nearly twice the water. Common in older work and in jobs where the installer sized for flow without thinking about the wait.

No insulation on the hot line. Uninsulated pipe loses heat between uses, so the water sitting in it is cold even if it was hot an hour ago. This is the cheapest fault to fix and the most common one.

A dead leg. A branch that was capped off or a fixture that was removed, leaving a length of pipe with water sitting in it permanently. It steals heat from the live line every time.

A tempering valve too far from the outlet. The valve mixes the water down, and everything downstream of it is part of the wait.

Low flow at the outlet. The narrower the flow, the longer it takes to clear the pipe. A partly blocked aerator makes the wait worse, which ties into the broader [water pressure](/blog/water-pressure-problems-in-apartments) diagnosis.

The three fixes

Insulate the hot line. Cheapest, least disruptive, and it helps every time. It does not shorten the wait on the first use of the day and it makes every subsequent use much faster, because the water in the pipe is still hot.

Move the source closer, or add a second one. A small unit serving the kitchen, or an instantaneous unit at a distant bathroom. Costs more, and it removes the problem rather than reducing it.

Recirculation. A loop that keeps hot water moving so it is at the outlet when the tap opens. The complete answer, and the one with ongoing cost.

How recirculation actually works

A return line carries water from the far end of the hot line back to the unit, with a small pump keeping it moving.

Done badly it wastes a great deal of energy, because the pump runs continuously and the pipe loses heat all day.

Done properly it is controlled: a timer matched to when people actually use hot water, a thermostat so the pump only runs when the loop has cooled, or a demand control where a button or a sensor starts the pump when somebody is about to use the tap. Insulation on the whole loop is not optional.

In a strata building a recirculation line is common property, and installing or upgrading one is a capital item rather than a maintenance one. So is the question of who pays for the energy it uses, which is worth settling before it goes in.

What it costs to leave it

Worth putting a figure on for a building, because it changes the conversation.

Two minutes of water down the drain, several times a day, across every apartment in a building, is a real volume of water on a bill somebody pays. In a metered building it shows up in the common water charge.

Then there is the tenant experience, which for an agent is the part that generates the calls.

Diagnosing it properly

Time the wait at each outlet and write it down. Check whether the hot line is insulated, anywhere you can see it. Look for capped branches. Check the outlet flow.

Most of the time the answer is insulation and a dead leg, and neither needs a new hot water unit. Replacing a working unit because of a long wait is a mistake we are asked to make fairly often, and it changes nothing.

Ample works on hot water systems across apartment buildings and houses in the eastern suburbs and inner city, with the plumbing and the electrical handled by one team.