Do you currently have forced air heating? Are you considering replacing the water heater in your home? Did you know that with a regular hot water tank, vented either up the chimney or out the wall (power vented), 50 cents of every dollar is going into thin air, not into your hot water and that mid efficiency furnaces and boilers have a real life efficiency of only 70%?
You have choices and since you’re considering a solar water heater, it is also time to think about your back up heater, both for domestic water heating and possibly for space heating as well.
In situations where there is a lot of hot water used and the tap stays on, a tankless gas heater may be the way to go but for those with small hot water demands, such as one or two people in the home, a high efficiency tank should be considered. Here is why:
Suppose you turn on the tap for 30 seconds to wash your hands. The tankless heater has to recognize the water flow, light the unit, get the water up to temp and get it to the tap before you are finished. As most heaters are 20 to 30 or more feet away from the tap, this seldom happens with hand washing and often results in gas and electricity wasted with poor results. the best situation is to wash hands in cold water but that doesn’t work for everyone.
High Efficiency Tanks
It may be better to use a high efficiency tank which won’t turn on for a few litres of water flow. While 10 years ago, there were few if any reasonably priced high efficiency tanks on the market, that is not the case now and we can supply one for a cost a bit above the tankless heater. They are around 95% efficient and in some cases ( small heat load houses) can also provide the heating for whole house.
High efficiency tanks are better suited for use with a solar preheat then are tankless heaters but the decision about which one is suitable is based on individual circumstances.
A tank will wait for the tank temp to drop to its set point before coming on. In this way, you may be able to take numerous short draws of hot water without starting up the burner. This prolongs the life of the burner, controls and ignition systems.
Tankless Water Heaters
For tankless applications, we have picked the Navien tankless heater. At a published 98% efficiency, it is the most efficient unit on the market and with a stainless steel heat exchanger, it should be the longest lasting (most units have copper heat exchangers).
The tankless heater is an efficient method if you have a high usage. Most units on the market are about 82% efficient. They are a big step up from the low efficiency tank type. However, be careful about which units are suitable for use with a solar water heater. Some are designed with the assumption that the water coming into the unit is at city mains temperature (6-12C). With a solar hot water system this is not the case. A solar system can store and provide water temperatures up to 75C (although we limit this to 50C with the use of an anti-scald valve). The back up heater must be able to recognize the temperature of this hotter incoming water, and limit the amount of gas necessary to to meet the desired temperature of 50°C.
Also, beware of claims of a typical tankless heater giving 5-7 gpm of flow. This is wishful thinking and you will not achieve it. Tankless are best when the house is using low flow shower heads.
For those people with a boiler for home heating (floor heating, radiators etc.), we install the Viessmann Vitodens boilers. These boilers have high efficiency and the best built heat exchanger (which is one of the most important components in the boiler). They also, in my opinion, have the fewest set up problems and they continue working efficiently for years. The Vitodens boilers can come with a “combi” hot water package which will give tankless hot water as well as space heat.
Due to the time of use electrical rates, we can provide hot water for near the cost of natural gas. With a well insulated electric tank, and a timer which only allows the tank to heat during off peak times, we can reduce our carbon footprint to a very small level. This system may not be for everyone but when paired with a solar water heater, this system will allow most people to have a water heating bill of less than $100 annually.
For conserving homes Viessmann now has the Vitodens 222F. This boiler combines the efficiency and space saving ability of a combi boiler with a higher flow rate for hot water production, allowing faster tub fills and larger shower heads.