[pnguyen]

Topic: Plumbing

Question: is there an advantage in terms of cost and expenses to install a tankless water heater over a standard gas heated water heater tank? Assuming a family of 2 adults and 1 child and daily shower use. Would the energy you save from the constant heating by gas of a tank be offset by the electricity use of heating water with a tankless system? I'd like someone neutral and objective answer if there is such an objective answer.

[labman]

I dug into tankless water heaters a few years ago, and my crap detector went off. I have gas hot water, dryer, and furnace. The claimed savings exceed what I pay for gas in the summer time for both hot water and the dryer. If you are using anyway near the hot water calculations justifying a tankless heater assume, you might better look at using less hot water. We are careful to run full loads of laundry and dishwasher. I take nice hot showers, but not excessive long ones. I shut the hot water off between rinsing ny razor each time. Try to convince you wife she needs more clothes so she can always run full loads of laundry.

The stand by losses are exaggerated too. I have shut my heater off when we went away for a weekend. When I come back and turn it on, sometimes it has lost so little heat it doesn't even kick on. I hardly ever remember hearing the gas come on when nobody was using water. I think they use figures for the uninsulated artifacts of the 40's. So, I say dig into the figures yourself.

Although you can run out of hot water with a tank, tankless can be a pain too. For starters, the instant hot water is instant at the heater, not at your point of use. The wait is just as long, and just as much cooled off hot water goes down the drain. There is the minimum flow thing. Usually when I take a shower, I open the valve clear up and turn it all the way to hot until the hot water starts. I then cut back both the temperature and flow. If you are then drawing too little hot water, it shuts off. You get the temperature adjusted and step into the shower just as the no longer heated water reaches the shower. Then there is the heating to a differential, not a temperature. The water is heated up so many degrees. If the temperature of the incoming water changes, the temperature of the hot water does too. Having spent a couple of weekends at my daughter's house with one of the infernal things, I am even happier I decided to stick with a tank.

I might mention, my views on this subject are not popular with those here making their living selling and installing them.

I swear to God I in no way make my living selling hot water tanks, gas, or electricity. I just want to pass on what I have found out.

[iamgrowler]

Topic: Plumbing

Question: is there an advantage in terms of cost and expenses to install a tankless water heater over a standard gas heated water heater tank? Assuming a family of 2 adults and 1 child and daily shower use. Would the energy you save from the constant heating by gas of a tank be offset by the electricity use of heating water with a tankless system? I'd like someone neutral and objective answer if there is such an objective answer.

If we were talking about a gas fired tankless system, then I could vouch for it's energy ratings and claims after asking a few pointed questions about it's intended use, but the cards are off the table when vouching for electric tankless heaters.

I'm curious, why are you set on an electric unit if you have the option to go with a gas fired unit?

[catgita]

I currently use both a large whole house demand water heater and a point of use electric heater. They are hard to recommend as a retrofit due to indirect costs, but do have some advantages. This is my second house with demand heater. Here are my findings:

Whole house: Tankless is much more expensive and payback is about 20 years, including the fact tanks have to be replaced 3 times as often. You won't run out of hot water. Tankless saves a lot of space. Large tankless need the equivalent of a bathroom sink (with aerator) on full to turn on, and if you turn it down much, the pipe fills with cold water. Some models have thermostats and start at relatively low flow, but have noisy fans. They require a very large gas supply line, which can exceed the cost of the heater. With adaquate gas line, the flow controlled units do output consistent relative water temperature. Hot water recirculating pumps are not compatible with demand heaters (other than for space heating). It is best to keep the temperature set relatively low so more water flows through the heater and keeps it running.

Point of use: These draw A LOT of power (3500w for a bathroom sink to get warm only). The heater is cheap (about $200) but the dedicated circuit is expensive. It cuts the wait down to almost nothing. It turns on at a very low flow rate. They are available with thermostats but still produce inconsistent temperatures. They make a moderate clacking noise when they turn on (power relay).

I installed the whole house unit to save space in a house with minimal storage. I installed the point of use heater in-line with the main heater at a remote location to decrease the wait and save water.

By rigging a pressure regulator as a bypass, I was able to use the small POU to serve two sinks, bathtub, dishwasher and laundry without restricting flow. If demand exceeds the capacity of the small booster, the hot water from the main heater arrives quickly anyway, and the POU shuts off by its thermostat.

If I were doing a major remodel, I would use two medium size tankless heaters; one near the master bath, the other near the kitchen. This would provide quick hot water near where it is used without the waste of space and efficiency of two tanks. It would be an expensive luxury, however.

[labman]

I hope you aren't storing combustables within it the required clearances of a gas tankless heater. It may be small, but you have limits on what can be near it.

[catgita]

This brings up another point: my tankess water heaters are mounted to walls much closer to the primary point of use than the old water heater closet. This not only decreases time and heat loss, it frees up the old water heater closet for other use.

There is nowhere on the exterior of my house where I could put a heater cabinet, but the tankless works fine (and is permitted) outside in my climate. It survived one of the coldest winters on record without freezing. I also can use direct vent, so long as it is not near an operable window, so no chimney pipe (though the unused pipe in the old closet leaks).

Tankless still only seems worth while if you have special circumstances.

[labman]

I think they are really designed to go outside. By the time I got to that option, I was too disillusioned over the hype on the energy tanks use to be interested.

[iamgrowler]

This brings up another point: my tankess water heaters are mounted to walls much closer to the primary point of use than the old water heater closet. This not only decreases time and heat loss, it frees up the old water heater closet for other use.

Most of the installs I do are in new construction or remodels.

To decrease time and heat loss I generally plumb from a manifold located just a few feet from the tankless heater and then pull insulated 1/2" homeruns to each fixture. The warm water wasted in a 40 or 50 foot run of 1/2" piping is minimal, and likely even less than that from a conventionally plumbed system with a gas fired storage tank.

Most people who put these tankless systems down don't seem to realize that the cost savings isn't just in the tankless heater itself, but in how the delivery (piping) system is engineered as well.

A retrofit installation into an existing system isn't going to be nearly as energy efficient as an engineered system.