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When my water heater last needed replacing I went and got a Propane Condensing Gas Tank water heater[1]. It was a bit expensive up front, but at 96% efficiency

When my water heater last needed replacing I went and got a Propane Condensing Gas Tank water heater[1]. It was a bit expensive up front, but at 96% efficiency I thought I would make up the difference on gas while enjoying the performance. It is pretty wild - we lost power for days once in the winter cold, and it brought the water back up to temperature in under 10 minutes. Even empty it can basically keep up and heat like a tankless unit would. It has a little LCD panel where you can check the stats of the unit, so I just took a look. We've had the heater on for 3430 days, it has cycled 15,584 times, and run the burner for 57 days. It has basically run about 1.5% of the time it has been on. In the future I'd consider going the heat pump route if I can get solar, but given the topology and how my house is positioned it doesn't look like I'm a great candidate for it :-(. [1] https://www.hotwater.com/water-heaters/residential/high-efficiency-gas-tank/ https://www.hotwater.com/water-heaters/residential/high-effi...

teruakohatu 6y ago
I had not heard of Condensing Gas Tank water heaters before. They are very clever. Gas water heaters are very popular here in New Zealand. Do you know how much more efficient the Condensing Gas Tank water heater is over regular gas? If I understand it correctly, the difference is that the condensing system pre-heats the cold water with the exhaust gas from the burner. https://www.hotwatercylinders.nz/images/source/Bosch_26eco_Condensing.jpg https://www.hotwatercylinders.nz/images/source/Bosch_26eco_C... Did you compare costs of a regular gas heater vs. condensing?
- elric 6y ago
  Best case, a condensing heater uses 20% less gas than a conventional one. But there are some caveats...in order to condense the exhaust fumes, the returning water has to be cold enough. Low temperature radiators or underfloor heating are best for that. If you have huge, old, cast iron radiators that get super hot and stay hot for a long time, there probably won't be much condensing going on. Basically any time you see white smoking coming out the flue, it's not condensing.
- agent86 6y ago
  I believe a standard gas water heater is about 78% efficient, for a net gain of 18%. It does generate condensate, but since my gas furnace is near by I was able to set it up to use the same drainage system. The unit was about $2500, versus probably something like $1000 for a more "standard" power vent unit. So $1500 to make up, worst case. It burns 100,000 BTU an hour when it runs. A gallon of propane is about 91,500 BTU. So every hour is around 1.1 gallons of propane. The unit has run for 1368 hours so far, resulting in it consuming around 1505 gallons of propane. Assuming I would have used 18% more propane for a regular heater, that would mean 271 gallons saved. Propane cost fluctuates a lot here, but if we just run with a $2.50/gallon average, then it has saved me something like $678. There are a bunch of things I don't know though. For example, I don't know if this unit retains the heated water better than their lower/standard ones. I suspect it does given how infrequently it runs. It's design is also supposed to maintain its efficiency as it ages versus losses from a "standard" burner setup. True story or marketing shenanigans, I don't know. I was able to take advantage of a government program at the time to get a tax incentive on the heater due to its efficiency. I don't remember the exact amount, but I'm likely about even on it now between the incentive and the recoup. But, discarding that, I'd be about 50% recouped and have had a great hot water experience. It just never runs out, it rarely runs when there isn't an active draw, it only operates for minutes when it does run, it's LCD/metrics scratch my geek itch, and it's probably the best I can do for the environment given my constraints.
twic 6y ago
Is a condensing gas tank water heater what we in the UK would call a condensing boiler? If so, in the UK, it's been legally required that all new boilers are of this type since 2005. I'm a little bit surprised they aren't better known in the US.

teruakohatu 6y ago

I had not heard of Condensing Gas Tank water heaters before. They are very clever. Gas water heaters are very popular here in New Zealand. Do you know how much more efficient the Condensing Gas Tank water heater is over regular gas? If I understand it correctly, the difference is that the condensing system pre-heats the cold water with the exhaust gas from the burner. https://www.hotwatercylinders.nz/images/source/Bosch_26eco_Condensing.jpg https://www.hotwatercylinders.nz/images/source/Bosch_26eco_C... Did you compare costs of a regular gas heater vs. condensing?

elric 6y ago
Best case, a condensing heater uses 20% less gas than a conventional one. But there are some caveats...in order to condense the exhaust fumes, the returning water has to be cold enough. Low temperature radiators or underfloor heating are best for that. If you have huge, old, cast iron radiators that get super hot and stay hot for a long time, there probably won't be much condensing going on. Basically any time you see white smoking coming out the flue, it's not condensing.
agent86 6y ago
I believe a standard gas water heater is about 78% efficient, for a net gain of 18%. It does generate condensate, but since my gas furnace is near by I was able to set it up to use the same drainage system. The unit was about $2500, versus probably something like $1000 for a more "standard" power vent unit. So $1500 to make up, worst case. It burns 100,000 BTU an hour when it runs. A gallon of propane is about 91,500 BTU. So every hour is around 1.1 gallons of propane. The unit has run for 1368 hours so far, resulting in it consuming around 1505 gallons of propane. Assuming I would have used 18% more propane for a regular heater, that would mean 271 gallons saved. Propane cost fluctuates a lot here, but if we just run with a $2.50/gallon average, then it has saved me something like $678. There are a bunch of things I don't know though. For example, I don't know if this unit retains the heated water better than their lower/standard ones. I suspect it does given how infrequently it runs. It's design is also supposed to maintain its efficiency as it ages versus losses from a "standard" burner setup. True story or marketing shenanigans, I don't know. I was able to take advantage of a government program at the time to get a tax incentive on the heater due to its efficiency. I don't remember the exact amount, but I'm likely about even on it now between the incentive and the recoup. But, discarding that, I'd be about 50% recouped and have had a great hot water experience. It just never runs out, it rarely runs when there isn't an active draw, it only operates for minutes when it does run, it's LCD/metrics scratch my geek itch, and it's probably the best I can do for the environment given my constraints.

twic 6y ago

Is a condensing gas tank water heater what we in the UK would call a condensing boiler? If so, in the UK, it's been legally required that all new boilers are of this type since 2005. I'm a little bit surprised they aren't better known in the US.