The Pros and Cons of Tankless Hot Water Heaters
From time to time we invite experts in their field to contribute to our Homestars blog. Debra Fenwick of Fenwick Design Group has been advising her clients on the “green” renovation options for a few years now. One of the subjects that comes up frquently is whether or not the client should install a tankless hotwater system. I’ll let Debra take it from here…
The Pros and Cons of Tankless Hot Water Heaters
By: Debra Fenwick, Fenwick Interior Design
Working Hot Water Heater
Your water heater is typically the #2 energy user in your home and can use between 18-20% of the energy budget. Much buzz has been generated by the press and in environmental circles as to the benefits of the tankless hot water system earning it the reputation as the “eco-choice”. But what are the real pros and cons to this system and should it be an integral part of a green home renovation?
The tankless hot water heater (or “on demand” unit) heats water as you use it instead of storing hot water like a traditional system. It’s available in propane (LP), natural gas, or electric models.
The benefits are that it is a compact system which virtually eliminates standby heat and energy losses. When installed at a specific faucet or shower, it can provide warm water at remote points of use thereby decreasing the water wasted waiting for the warm water to travel from the main tank. The unit can provide unlimited hot water as long as it is operating within its capacity. And therein lies the rub…
Discussions with Nick Tilelus, partner at Paul’s Plumbing Ltd (416-759-7491) confirm that one of the main disadvantages of this system is that it doesn’t provide the necessary capacity for the needs of a typical family household. For example, it is unlikely that a shower and dishwasher can be run simultaneously. There is also an approximate 10-15 second delay before the water is heated sufficiently for use thereby increasing water waste. Pricing for the unit itself is several times higher than a regular tank. Gas units may require a larger gas line or additional venting and electric heaters draw more power (160,000 BTU vs 40,000 BTU’s for the traditional tank) thereby requiring multiple circuits and/or heavier cable all of which increase the installation costs by 2-4 times. The energy savings is only maximized in a gas unit when the pilot light is kept off when the heater is not in use and in areas of the country where electrical rates include a peak demand charge, operation of the electrical unit can actually be more expensive than the typical hot water tank.
Tankless Hot Water Heater
The tankless system will be most effective for a home with 1-2 people requiring a limited hot water supply. Unless a unit is installed at each faucet (with the associated higher costs), it is not a system that would be recommended for a large family home where showers, laundry and dishwashing is done simultaneously.
Systems aside, the potential home improvements most effective for energy savings are:
- Reduce water heater temperature setting to 120 degrees (140 degrees for homes with an automatic dishwasher)
- Insulate water heater tank and pipes to reduce standby losses and maintain water temperature longer (for best results wrap both the cold and hot water pipes entering the tank and top and sides of tank down to the lower element)
- Install low flow showerheads and water flow restrictors on showers and faucets to reduce water use and cost
- Consider installing a heat recovery water heating system on existing a/c system
- Consider installing heat exchanger devices below showers which recapture approx. 60% of heat in the drain returning it to the water heater
Energy usage and environmental impact are key elements when choosing a new water heating system. The best advice is to calculate your hot water needs in order to determine which system will work best for your household while using the tips noted above to get the most out of whichever system you choose.
Debra Fenwick is an interior designer and LEED Accredited Professional working in the Toronto area .
http://www.fenwickdesigngroup.com
Posted by CathyR
December 17th, 2008 at 4:12 pm
Having lived with a tankless heater for almost a year now, I believe there are some inaccuracies in this article. We are a family of 4 with 2 teenage sons. Both boys are in sports and it seems the washer is constantly running in our house. We often have 2 showers in use at once. We have had very few situations when the unit could not supply enough hot water. Our gas bill in the summer (where heating water is the only use of gas) is down to one third of what it was previously. And we really don’t find there is any more delay in getting hot water at the tap. About the only difference we have found is that my wife has to wait a bit longer to fill the bath tub. The tub faucet is one of, if not THE highest flowing water outlet in the house, and with the tankless system we find the flow is about half of what it was with a regular tank before. We believe the extra wait to the fill the tub is worth the 2/3 savings in natural gas costs.
The most important advise we can give is to make sure the proper size unit is installed. The units are sized by flow rate, and your contractor should talk with you about your water usage habits before recommending the appropriate heater model.
December 28th, 2008 at 3:26 pm
Thanks, that was helpful. I think this could work for me in a country cabin that I usually stay in alone, but will sometimes have up to five staying over. It could end up a retirement home. So many nay-sayers, it is good to hear from someone who has lived with the system for a while.
January 2nd, 2009 at 8:59 pm
This article talks of gas and electrical sources for running the system? What about the solar tankless heaters that are currently advertised? Does this affect the quality or service of the tankless system?
January 6th, 2009 at 1:05 pm
We have been installing a number of solar hot water systems combined with tankless water heaters and have had great results.
There are many advantages to combining the two systems.
1. The preheat water from the solar increases the flow of hot water out of a tankless unit because the amount of hot water a tankless can provide depends on the input temperature. In other words they work on a temperature rise. A 45F vs. 70F vs. 100F will have very different levels of output.
2. The water is already warm or hot before entering the tankless unit and therefore the added wait time associated with a tankless unit can be reduced or eliminated.
3. Its important when combining a tankless and solar water heater to consider a tankless unit that recognizes incoming temperature and fully modulates its burner (only burns the necessary amount of gas to rise the temperature by appropriate amount). With the right tankless unit, when the solar is doing its job perfectly, the tankless unit won’t turn on.
We have a customer who has been monitoring their tankless/solar system and have told us that their gas consumption through july and august was just 1m3 and cost them just 14 cents.
If anyone would like to discuss this I can be reached at 416.400.4747.
January 6th, 2009 at 1:06 pm
I forgot to mention that in regards to point number 1 above, since the gallons per minute of hot water are increased from the solar preheated water you would be able to run more showers and appliances at the same time.