On-Demand Tankless Water Heaters - Propane vs. Electric (AC, tank, sink)

[cnwinger]

Hello,

I am building a new house and I am in an area that is Propane-only. I am putting in 2 Tankless Water Heaters, which as of right now are planned to be Rinnai brand Propane Tankless water heaters.

However, since I'd like to go Solar in the future and I plan on living here for 10+ years, I'm considering switching these to 2 Electric Tankless water heaters.

Can anyone comment on the pros/cons of each? Is the per-unit cost of initially purchasing these similar regardless of whether I choose Propane or Electric? It's confusing me because I've read that Propane versions have a higher initial cost to purchase, and I trun around and read the opposite (that Electric versions cost more to purchase).

Thanks...

[Nonesuch]

I have a Rinnai tankless and am on a well, so my incoming water is usually 50F, sometimes colder. I've never had any issues with the Rinnai not being able to keep up with heating the water even on the coldest winter days.

If you are on a well and bring water into a basement, consider installing an oversized pressure tank (or two) in the basement to give ground water a chance to come up to about 60F before it feeds the water heater.

Originally Posted by cnwinger

I am building a new house and I am in an area that is Propane-only.

Propane only, or piped in natural gas? If natural gas, that is the cheapest heat you can get (other than solar or maybe a heat pump).

I assume you're installing gas for other purposes, not just to run the water heaters?

Originally Posted by cnwinger

Can anyone comment on the pros/cons of each?

Gas-fired tankless is cheaper to run than electric-resistive tankless, and will keep up better in a whole-house role. Electric is easier to install as point of use (POU, for example under a kitchen sink to bring water up to 120F for dish washing), but anything beyond that (like your 1/2 house installation) needs special wiring and dedicated breakers to handle the amperage draw, and almost certainly won't be able to keep up if your incoming water is really cold; either flow slows to a trickle or hot water is more like lukewarm.

Originally Posted by cnwinger

I'd like to go Solar in the future and I plan on living here for 10+ years

I seriously doubt solar cells are going to be able to drive an electric tankless water heater, resistive heating draws too much power all at once. Some people install an electric storage water heater in front of any other heater and use it as a 'dump load' for their solar system.

When you do install solar, why not skip the electric inverter and get a solar water heater? You can put a solar-heated water storage tank inline before the water goes through the tankless heater, reducing the amount of work your tankless heater has to do to get the water up to 120F.

Originally Posted by cnwinger

Is the per-unit cost of initially purchasing these similar regardless of whether I choose Propane or Electric? It's confusing me because I've read that Propane versions have a higher initial cost to purchase, and I turn around and read the opposite (that Electric versions cost more to purchase).

I suspect the differences in installation costs are quoted by people retrofitting an existing home, where the real cost is if you had a storage heater on electric and are putting in all new gas and venting, or had a gas-fired storage heater and need to put in all new electric hookup. For new construction, where you plan to hook up to gas anyway, the cost to install electric might be a little cheaper, just because of the lack of venting.

[cnwinger]

Thanks for the reply. I am in a Propane-only area (no natural gas available) and I am on City water. I am located in SoCal, so low water temps shouldn't be too much of an issue.

I wasn't aware that the Electric water heaters used that much power. So if I go with Propane tanlkess units now, I can add the solar-heated water storage down the road, and then I'll use less propane? What's a ballpark for the reduction? (50%?) My goal is try try to reduce utility costs as much as possible. I know that propane is expensive in my area. I will already have Propane running to my kitchen range and to my BBQ.

[chet everett]

There is no way that a tankless propane or electric water heater makes sense if you are in a climate like SoCal where heat pump based water heater is so much more efficient...

Heat Pump Water Heaters | Department of Energy

[COD1628]

If you are installing these for lower utility bills I don't think you are going to see a return on your investment for the thankless system. You should probably do some more research on it, but last time I looked into it, the ROI takes more then 40 years for the thankless systems to see positive numbers when compared to your standard tanked system. Reason being the tanked systems are a dime a dozen compared to the thankless and more and more efficient with every passing day.

Also, any heating system draws ALOT of amperage regardless of the applications (cooking, heaters, etc.) and your standard solar powered system is more designed for lower amperage applications. The cost of green energy has a very high upfront and maintenance cost, which is why you don't see it installed right now for saving money. It's done for footprint reasons, and even then that is a whole different debate on the repercussions of production.

[cnwinger]

I have not looked into heat pump systems. So I can install an Electric Heat pump system in my 3-car garage or my attic? And then I can utilize the solar power down the road to assist with the electricity usage? And it sounds like, as a side benefit, they would cool down my (often terribly) hot garage?

What initial cost difference am I looking at? I currently have 2 tankless systems planned for a 3200 sq ft home.

[chet everett]

Originally Posted by cnwinger

I have not looked into heat pump systems. So I can install an Electric Heat pump system in my 3-car garage or my attic? And then I can utilize the solar power down the road to assist with the electricity usage? And it sounds like, as a side benefit, they would cool down my (often terribly) hot garage?

What initial cost difference am I looking at? I currently have 2 tankless systems planned for a 3200 sq ft home.

Though the upfront costs of the heat pump water heaters are pricier than basic gas or electric tank types, they're price competitive with tankless units -- about $1600 for the 80 gallon. http://www.appliancesconnection.com/...r-i392009.html
Price aside, the benefits are enormous -- tremendous efficiency, minimal maintenance, no combustion, easy integration into "smart" homes with vacation mode and online monitoring and "free" cooling of space like the garage that probably will make more of the sq ft more usable for either storage or workshop / home gym.

Assuming your 3200 sq ft is sized for a family of 5-6 a single 80 gallon unit will deliver more hot water faster than a traditional electric water heater: Rheem Professional Prestige Series: Hybrid Heat Pump Series

GE GeoSpring Heat Pump Water Heaters - WayneWhiteCoop.com

There are several ways to incorporate "off grid" type units into a design as well -- Heat-Pump Water Heaters | Home Power Magazine

[cnwinger]

Thank you Chet, this is all incredibly helpful.

So if the Heat Pump heater you linked above has an average yearly cost of ~$200 (which I could further reduce in the future by going solar), what do you think the ballpark comparable yearly cost would be for the setup with the 2 Propane Tankless heaters?

In addition, is it possible to setup a more affordable propane tankless heater just on the far side of the house, to provide faster hot water, and then shut off once the water from the heat pump heater arrives? The only real downside to the setup you describe is waiting for hot water to arrive all over the house.

[chet everett]

If you are still in the "planning" stage and have not actually begun building this home the smartest way to address the "furthest from the tank" issue is with a well designed circulation loop hot water pipe layout -- Hot-water circulation loops - Fine Homebuilding Article

You do not need (nor would be sensible...) to add "on demand" tankless hot water heater(s) in an energy conscious new home!

[thecoalman]

Originally Posted by cnwinger

Thanks for the reply. I am in a Propane-only area (no natural gas available) and I am on City water. I am located in SoCal, so low water temps shouldn't be too much of an issue.

I wasn't aware that the Electric water heaters used that much power. So if I go with Propane tanlkess units now, I can add the solar-heated water storage down the road, and then I'll use less propane? What's a ballpark for the reduction? (50%?) My goal is try try to reduce utility costs as much as possible. I know that propane is expensive in my area. I will already have Propane running to my kitchen range and to my BBQ.

If you live in warmer climate where removing heat from the home is desirable look into the heat pump water heaters. They use 1/2 to 1/3 the electric compared to regular electric and if you already cooling the space with AC it can take some of that load.

If you have a few months or whatever where you might be heating the home get one that can be switched to regular electric when you are putting heat into the home. You could also consider installing it unheated space like the garage or whatever. You don't want it in heated space using heat pump mode, this will have the opposite effect and drive up your energy costs.