Everyone is more or less familiar with the conventional system of the hot water tank and the furnace. But the hot water-on-demand and combi boiler systems can replace both of these with great benefits to homeowners. On our podcast, All Things Renovation, we interviewed Matt Gyorfi from Pro-West Sales, a plumbing and heating distributor in the Lower Mainland to educate our listeners about what these benefits are. Here’s a summary of what we learned from him.

What exactly are these new systems and how do they replace the conventional systems?

A conventional hot water tank constantly maintains a body of water at a minimum of 140 degrees Celsius, 24 hours a day, 365 days a year. Conversely, an on-demand tankless unit hangs on the wall and only produces hot water as you use it. A hot water tank is only 60-67% energy efficient, whereas the on-demand tankless unit is 95-99% efficient.

A combi (combination) boiler system combines the on-demand tankless unit on the wall with a hydronic furnace. This leads to greater efficiency with both hot water and heating your home.

What size of footprint do these units take up in your home?

A normal mechanical room, hidden away in a central location in your house, might be roughly 5′ by 5′ in size. If you’re doing a renovation, particularly in a basement, you can actually regain that square footage into your living space because you’re hanging the units on the wall. So rather than having a room, your whole system can occupy a 3′ by 3′ box instead!

A tankless water system requires a two part venting system. You need one pipe that brings air in for combustion, and another pipe to take exhaust out. Since you’re simply hanging the unit on the wall, it no longer even needs to be located in a dedicated mechanical room. It can be placed in another room or on an exterior wall in the house. This dramatically decreases the length of the venting pipes that the system needs, from 20′ to 60′ down to just a few feet.

These systems no longer need to be located in a mechanical room.

What else do homeowners need to consider?

Pressure Reducing Valves

Most homes have Pressure Reducing Valves (PRV) on their domestic hot water, which reduces the pressure of the water coming into the home from the main water line. These units need about 60 psi of pressure, which is fairly standard on newer homes.

Recirculation

The on-demand unit is waiting for someone to turn on the faucet. Once the flow sensor detects water, it will start the activation of generating hot water. That sequence of events can take a little bit of time. So something the homeowner might want to consider is some sort of recirculation. This can be done in several ways:

An external recirculation loop. This is a line that runs from the mechanical room to the tankless unit to the furthest faucet. However, this is impractical in a retrofit situation as you’re not going to be opening up walls to install it.
The Navien NPE-A unit has both the external option, as well as an internal option. This uses a tiny hidden buffer tank about the size of a hot water bottle. It recirculates the water the water through the heat exchanger. When someone turns on a faucet it’s already generating hot water so it’s deployed much faster.
The NaviCirc. The home’s hot and cold lines are turned into recirculation lines. The NaviCirc is mounted on the furthest faucet. You will get hot water extremely fast but when the homeowner turns on the cold water, there will be a tiny bit of hot water that comes out as the unit corrects itself. Then the cold water will start flowing.

Let the tankless unit act as a mixing valve

Water that is stored in a tank needs to be heated to a minimum of 140 degrees Celsius to meet building codes. Some people want their tankless hot water systems set to 150 degrees or higher, but why heat the water up, only to mix it with cold water at your faucet? You are losing a lot of efficiency (and money) that way. Set the tankless unit to run at as low a temperature as possible so that it acts as your mixing valve.

What are the power requirements?

Tankless units use very little power. A 15 amp breaker is all that’s needed and generally there is one close by in the mechanical room. It’s only a spark-ignition, a fan, and a few basic motors inside.

Is the combi boiler system as effective for heating and cooling a house?

Heat pumps aren’t as efficient at heating the house at very low temperatures. The iFlow hydronic furnace doesn’t care where the heat comes from (heat pump, boiler, Navien tankless unit). It can choose when you switch over from your heat pump to natural gas, depending on the temperature outside. Natural gas is more financially effective, but there is a carbon footprint.

If homeowners have an inverter (modulating) heat pump, there is a zoning option with the iFlow unit that allows you to set up 4 zones for air-conditioning in the house.

When would a system like this not be advisable?

The limitations on these systems are the domestic load, ie, too many people and appliances are being used at the same time. But these systems are highly configurable to different sized homes and multiple family living situations.

There is a lot of push from cities and building codes to be more energy efficient. What are the current incentive programs?

Fortis BC is offering a $1000 rebate for tankless hot water heaters, and $1200 for combination systems. In addition there is a $300 top-up bonus for combining 2 appliances (space heating and domestic hot water). Periodically they offer different incentives, like doubling the rebates.

What is the average savings if your usage stays the same?

It’s tough to say as everyone’s usage will be different but generally it’s a 10-30% reduction in your energy costs.

What sort of application is there for technology?

Navien has a product called the NaviLink that you can pair to any of the Navien devices. It gives you control of the recirculation (on/off, window of recirculation, gas usage patterns).

I strongly encourage homeowners to ask their contractors about outdoor reset. This involves a sensor that is placed outside and provides the temperature to any condensing appliance (condensing boiler, boiler, tankless water heater with certain combinations). The unit will then know what to do, and it will create a hotter water temperature as it gets colder outside. It will also lower the set point temperatures – for every 3 degrees Celsius that you lower the water temperature, you save 1% on your utilities.

What about maintenance?

The iFlow hydronic furnace has similar maintenance to a regular furnace – you need to change your filters. It has a constant CFM (cubic foot per minute), meaning that it has the capability to go from 0% to a 100% pushing air flow capacity. So if it senses too much pressure from a dirty filter, it will automatically increase the pressure going out to the system. If the filter hasn’t been changed for years it can sound like a jet engine as it tries to push all the air through the dirt!!

A conventional hot water tank is an open vessel that collects lots of sediment in the bottom. This is because it’s running at higher temperatures. A tankless hot water system runs at much lower temperatures, especially if it has an outdoor sensor, so you don’t get as many minerals out of the water. But there is still a citric-acid based flush that you need to do once a year through the heat exchanger. This should be done by a contractor or technician to do it as they will do a more complete check than a homeowner generally would.

The three main things to look for in water quality are hardness, total dissolved solids, and manganese. So if you’re within the normal parameters, then you’re fine. If not, your system will need more frequent servicing.

To listen to the full episode and read the show notes, visit www.AllThingsRenovation.com

Hot Water on Demand & Combi Boiler Systems