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Learning, Sharing, and Teaching => Ask a Mustachian => Topic started by: andyp2010 on October 09, 2015, 03:20:17 PM

Title: Electric Tankless Water Heaters
Post by: andyp2010 on October 09, 2015, 03:20:17 PM
Needing to replace my original 1950's hot water cylinder soon anyway, I've been looking at my options.

Was going to go with instant gas, however it looks to be expensive to install and it requires me ordering bottles every few months.

I'm not willing to go for anything with a tank as it can't be more efficient to have 200 litres sat in your cupboard at 70c day and night.

I've just come across this - http://www.amazon.com/Rheem-RTE-13-Electric-Tankless/dp/B003UHUSGQ/ref=sr_1_2?ie=UTF8&qid=1444423966&sr=8-2&keywords=rheem+ecosense

This would save me on install costs, means I don't have to have flammable liquids attached to my house, don't have to make a concrete stand for the bottles and it can be put in essentially the same place as the current cylinder (slap bang in the middle of the house).

Now I see that it could make sense for someone in the US where electricity is 6c/kwh or something but in nz its equivalent to US 15c/kwh. Is it still viable? Does anyone have any comparisons? There will be 5/6 people in the house. How do you know what's big enough? There seems to be little info online about them and I trust you guys over average joes.
Title: Re: Electric Tankless Water Heaters
Post by: AZDude on October 09, 2015, 04:28:01 PM
How cold does it get there? In warmer climates tankless can make sense because the water is already luke warm and it takes less energy to heat it up. The colder the winters, the more powerful water heater you will need and the more hot water you will want.

If you live in Miami, tankless might make sense. In New Zealand(its cold there, right?), probably not.
Title: Re: Electric Tankless Water Heaters
Post by: abiteveryday on October 09, 2015, 04:30:12 PM
Surprising as it might sound, with 5/6 people in the house you might really truly come out ahead with a modern tank style heater.   
Title: Re: Electric Tankless Water Heaters
Post by: JLee on October 09, 2015, 04:34:43 PM
From your flammable liquids reference, I assume you currently have a gas water heater?  Electric is far less efficient at heating - I'm not sure this'll work out how you want.

http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/water-heaters/tankless-water-heaters/overview/tankless-water-heaters-ov.htm

http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/tankless-water-heaters.html
Title: Re: Electric Tankless Water Heaters
Post by: Jeremy E. on October 09, 2015, 05:04:00 PM
I think MMM recommends a heat pump water heater in this article,
http://www.mrmoneymustache.com/2015/03/25/cut-your-power-bill/

Here is the specific ones he links to
https://www.gpconservation.com/water-heaters/heat-pump-water-heaters.html
You might be able to get a discount if you use the coupon code MMM(just a discount, he get's no comission from the deal)
Title: Re: Electric Tankless Water Heaters
Post by: andyp2010 on October 10, 2015, 03:15:46 AM
I'm running full electric at the moment, no gas.

Surprising as it might sound, with 5/6 people in the house you might really truly come out ahead with a modern tank style heater.   

Looks like everyone's in agreement that instant electric heaters are shit, think I'll rethink. It would be reasonably cheap to put a decent cylinder in. With recent events there's a lot of 1 or 2 year old Rheem cylinders kicking about second hand.

Cheers for the good links.

Title: Re: Electric Tankless Water Heaters
Post by: Axecleaver on October 10, 2015, 05:00:44 AM
US rates are in the 9c range only in the middle of the country. The Northeast and CA are in the 13-16c range. Hawaii is 34c (where solar is very popular) due to needing to import all their energy, first to the West Coast and then to the islands. Handy map: http://www.eia.gov/electricity/state/

Quote
How do you know what's big enough?
This is a function of flow rate (how much you use at once) and average temperature of the water coming in to the house. If you get water from a well, regardless of the season it's going to be at a constant and predictable temperature. Another handy map (for the US) http://www.thetankless.com/uploads/Average%20water%20temp%20map2.pdf.
Title: Re: Electric Tankless Water Heaters
Post by: Kroaler on October 10, 2015, 03:00:54 PM
Hey just as a side note.  If you get a tankless heater strong enough for a new house hold, you may (probably) will need to pull new wiring from breaker box.   Most home 220 lines to the water heater are too small for the current of a tankless.  Not saying you can't do it, but I do believe to meet the safe amp ratings you will need bigger wires pulled.    Keep that in mind if you get one.  I was going to get one then I realized I had to pull new wires and didn't feel like it...
Title: Re: Electric Tankless Water Heaters
Post by: frompa on October 10, 2015, 04:09:14 PM
Allow me to be a voice in the wilderness on the tankless water heater.  We had one put in last January to replace our old gas heated water tank system.  (We are in a city, so kept the gas line.)  Of relevance to your decision, though, a big factor in our deciding on this was our guys' assessment that because we are very light users (only two people, only use hot water for showers and washing dishes), tankless made sense.  If we were more people or otherwise had greater demand for hot water, keeping the tank would have been a reasonable option. 

As an aside, the tankless system has worked well, other than its making random, odd dinosaur-belching sounds. But to tell the truth, those sounds have enhanced our day to day enjoyment of life.  Such is our life!
Title: Re: Electric Tankless Water Heaters
Post by: music lover on October 10, 2015, 05:26:49 PM
Standby heat losses are often over exaggerated by the tankless companies. In reality, HW tanks do not lose heat that quickly. Also, if you live in a cool climate, any heat "loss" helps to warm the house and therefore, is not really lost. However, if you use AC a lot, then that loss has to be cooled.

This fellow calculated a 61 or 82 cent saving per month using tankless, which means the extra cost will never be paid back:

http://www.neo.ne.gov/neq_online/july2006/july2006.wiz.htm

More info on tankless:

http://michaelbluejay.com/electricity/tankless.html
Title: Re: Electric Tankless Water Heaters
Post by: andyp2010 on October 10, 2015, 11:36:25 PM
Ok, I've settled for being normal and not trying to beat the system. Doesn't mean I wont put a solar panel up at some point though ;)

Will probably end up only being about 700NZD to fit which will offset any small reduction in monthly savings, I've bought large, practically new cylinders for 300 bucks locally previously and labour shouldn't be more than 400 from a plumber friend of mine.

Cheers for the sound water heating advice.