Tankless water heaters are quickly becoming the new normal for residential plumbing systems. They outperform traditional water heaters in a few key areas, including energy efficiency, operating costs, and life expectancy. They are also less prone to developing certain issues and generally require less maintenance and fewer repairs. Nonetheless, there are a few minor drawbacks to having a tankless water heater or a few issues you may experience with this type of unit.
1. Insufficient Flow Rate
When you have a tankless water heater, you’re limited as to how much hot water you can use throughout your house at one time. Only so much water can flow through a tankless water heater and get heated, meaning you can only use so many gallons of hot water per minute. If you have a unit that doesn’t have a high enough flow rate for the size of your house, you could have issues with running two showers at the same time. The shower closest to the water heater will normally have fully hot water, but the shower further away can run cold. Similarly, your shower may not have water when your dishwasher or washing machine is running if the appliance is closer to the water heater than the shower.
The good news is that this sort of issue is easy to avoid by having an experienced plumber determine what flowrate you need to meet most of your hot water needs. A unit with a flow rate of 5-6 gallons per minute (GPM) will usually be sufficient for a two- or three-person household. If you have four or more people in your house, you’ll usually want to choose a unit with a flow rate of 7-10 GPM. You could get away with a lower flow rate, but it typically means you won’t want to shower when washing dishes or doing laundry.
2. Mineral Deposit Buildup
While tankless water heaters have a long life expectancy and typically last over 20 years, mineral deposits can greatly reduce their lifespan. Even if your home has fairly soft water, you’ll still have limescale and mineral deposits continually building up within the pipes inside the water heater. At some point, the deposits can build up so much that they act like insulation and prevent heat from flowing out of the unit’s heat exchanger into the water. That means the unit may no longer be able to heat the water to the correct temperature. An experienced plumber can sometimes repair the issue by replacing the entire heat exchanger. However, this is a fairly complex repair, and it will often be better to install a new water heater, depending on the age and overall condition of the existing unit.
Luckily, this is one of the easiest issues to avoid. All you need to do is run a descaling solution through the water heater, which will effectively remove all of the limescale. Descaling a tankless water heater is something you can typically do yourself. Nonetheless, it’s just as easy to have a plumber do it every year since they can also then inspect and service the unit at the same time. If your home has overly hard water, you’ll get better results by descaling your tankless water heater twice a year.
3. Water Flows Hot, Cold, and Then Hot Again
Professional plumbers commonly refer to this issue as a “cold water sandwich,” which occurs at specific times when a tankless water heater is in use. The term may sound silly, but it makes sense: Hot water flows first, followed by a blast of fully cold water in the middle, and then hot water again.
This “sandwich” effect mostly occurs when two people use the same shower back to back. If the second person turns the water on and immediately hops in the shower, they’ll typically have at least 30 seconds to a minute of hot water before the water starts running cold. Once the cold water starts flowing, it can take a minute or two or sometimes even longer before the water is fully hot again.
The reason the water initially flows hot when the second person turns the shower on is that hot water remains in the pipes between the water heater and the shower. The shower then starts running cold as soon as this remaining hot water is used up. That’s because it takes some time from when the tankless water heater turns on until the water flowing out of it gets fully heated. Once the water finally does get fully heated, you’ll have no issues and can shower as long as you want without the water running cold again.
While this effect isn’t a major issue, it can be unpleasant to suddenly get hit with cold water when showering. Luckily, it is easy to prevent by letting the shower run for a bit longer before you get in if another person showered right before you. If you’re concerned about wasting water, another option is to upgrade your plumbing with a hot water recirculating pump. This type of pump frequently runs alongside the water heater so that the water in all your hot water lines is constantly hot. The issue is that your water heater will run far more and have a shorter lifespan. Combined with the amount of energy needed to run the pump, your energy bills will increase by quite a bit.
A more effective option is to install a small point-of-use tankless unit that only supplies hot water to your shower. This route could still cause the sandwich effect, but it usually takes only a few seconds for the water to warm up.
4. Long Lag Times
Probably the biggest downside of having a tankless water heater is how long you normally have to wait for your water to get fully hot. This is again because it typically takes around 30-60 seconds from when the unit turns on until it can achieve the correct temperature. You also have to wait for the pipes the water flows through to fully heat before your shower is finally hot. If you have a sink or shower on the opposite side of the house from the water heater, it can sometimes take a few minutes to have hot water. If the long lag bothers you, you can install a recirculating pump or opt for point-of-use units instead of a whole-house unit.
As one of the most experienced plumbing companies in the San Jose area, Plumbtree Plumbing & Rooter has the skills to help when you need any water heater service. We install, service, and repair tankless and traditional units and are also the company to trust for the rest of your plumbing, drain, and sewer system needs.
If you’re considering a tankless water heater for your home, give us a call, and we ensure you get a unit that’s the right size and type to adequately serve your entire home.
