No, it doesn't take "days" for the water in the holding tank to cool down, at most it is hours. If you mean a holding tank with a recirculation loop, like the Naviens, that is very inefficient and actually worse than an external recirc loop. As others have noted, a tankless water heater with a tank is not a tankless water heater, just an inefficient tank heater.
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Tankless water heater capacity questions
- Thread starter ironwelder85
- Start date
finn
Well-known member
You’re correct. Gas tankless with a condensing loop do qualif. Electric and non condensing gas units do not.Yes, the Navien A series have just moved the recirc loop into the unit, with the corresponding reduction in efficiency.
Tankless do qualify for energy credits, since they reduce energy consumption by 25% to 50% and are more efficient than any tank heater can be.
The unit I installed in my outdoor sauna did not, since it doesn’t have a condensing boiler. There’s no good way to deal with the condensate, since the floor drain isn’t accessible, and outside drains are problematic in winter where the boiler is installed.
I guess the other installs done have magic tanks, cause they hold heat for a few days.No, it doesn't take "days" for the water in the holding tank to cool down, at most it is hours. If you mean a holding tank with a recirculation loop, like the Naviens, that is very inefficient and actually worse than an external recirc loop. As others have noted, a tankless water heater with a tank is not a tankless water heater, just an inefficient tank heater.
No ideawhy you think it's "inefficient". Tank water heaters are in millions of homes. An electric one is near 100% efficient. Standby loss isn't much. Plus that heat isn't "wasted" for 7-8 months a year as it just heats the area it is in a tiny bit.
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dcg9381
Well-known member
Think it depends on where you are. Around here our water heaters are often in the attic or garage, good places for them if you want to heat water. I can't get the hottub below 102 right now (heat induced from the circulation pump) without taking the cover off because it's darn hot outside..No, it doesn't take "days" for the water in the holding tank to cool down, at most it is hours.
I have the Naviens. They do have a 1/2 gallon "buffer" tank. So, to some degree they are traditional tanked heater, but if I recall right you can setup the internal recirculation loop to be off/on/on-demand. The on-demand function is pretty cool, you just press a (remote) button for hot water just before you need it and the system goes to work. These versions can be setup with an external recirc loop and don't require an additional pump. We use the recirc function to save water, as we're not on city water here and it's a limited resource.If you mean a holding tank with a recirculation loop, like the Naviens, that is very inefficient and actually worse than an external recirc loop. As others have noted, a tankless water heater with a tank is not a tankless water heater, just an inefficient tank heater.
How this would be less efficient than a tank of 50-100 gallons of water held at 120 degrees or so all day long, I don't understand? Well, unless ambient air is already 120 degrees....then I get it.
I've had roof mount solar water heaters also. 80 gallons in TX would last us about 3 days (no sun) - at least ~10 months out of the year.
It looks like Navien with recirc tank qualifies:
Gas Tankless Water Heaters (with internal buffer/recirculation tanks): Eligible Energy Star certified gas condensing tankless models qualify for 30% of the total project and installation cost, up to a maximum credit of $600
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I have no idea what an energy credit is.Looks like the Navien A series does have an internal buffer tank, and a recirculating pump.
In my opinion, they’re no longer tankless.
From what I remember, tankless water heaters don’t qualify for energy credits, as they don’t reduce energy consumption, I’d those credits still exist.
All they really do is provide unlimited hot water, and reduce the space footprint.
I have a tankless in my space constrained outdoor wood burning Sauna, and a hybrid electric heat pump in the house basement.
I prefer the hybrid heat pump, if you have room.
I just wanted a warm shop and to take a shower with no 34* water!
dcg9381
Well-known member
Tax credit.I have no idea what an energy credit is.
I think you are misunderstanding efficiency. I am referring to net energy consumption. An electric heater can be more than 90% efficient, in the sense that it converts nearly 90% of input power into useable heat, but it is inefficient for energy consumption, since it requires 25% to 50% more net energy to operate, due to the significant standby loss. That's why a tankless heater saves 25% to 50% of net energy over a tank heater.I guess the other installs done have magic tanks, cause they hold heat for a few days.
No ideawhy you think it's "inefficient". Tank water heaters are in millions of homes. An electric one is near 100% efficient. Standby loss isn't much. Plus that heat isn't "wasted" for 7-8 months a year as it just heats the area it is in a tiny bit.
It does depend on location and climate. In Phoenix Arizona they put tank heaters in the garage, where it is in the 120F range most of the year, so they rarely even turn on.Think it depends on where you are. Around here our water heaters are often in the attic or garage, good places for them if you want to heat water. I can't get the hottub below 102 right now (heat induced from the circulation pump) without taking the cover off because it's darn hot outside..
I have the Naviens. They do have a 1/2 gallon "buffer" tank. So, to some degree they are traditional tanked heater, but if I recall right you can setup the internal recirculation loop to be off/on/on-demand. The on-demand function is pretty cool, you just press a (remote) button for hot water just before you need it and the system goes to work. These versions can be setup with an external recirc loop and don't require an additional pump. We use the recirc function to save water, as we're not on city water here and it's a limited resource.
How this would be less efficient than a tank of 50-100 gallons of water held at 120 degrees or so all day long, I don't understand? Well, unless ambient air is already 120 degrees....then I get it.
I've had roof mount solar water heaters also. 80 gallons in TX would last us about 3 days (no sun) - at least ~10 months out of the year.
It looks like Navien with recirc tank qualifies:
A small buffer tank won't impact energy much, but the other discussion was about larger tanks that would impact efficiency.
That depends on usage patterns. In a normal household, the standby losses are much lower than that for an electric tank, because they are well insulated and don’t have a flue. Gas powered tanks have higher losses, because of the flue. But they don’t have 50% losses unless they are vastly oversized. The only places that see losses that high are infrequently used. Like a vacation house or something.I think you are misunderstanding efficiency. I am referring to net energy consumption. An electric heater can be more than 90% efficient, in the sense that it converts nearly 90% of input power into useable heat, but it is inefficient for energy consumption, since it requires 25% to 50% more net energy to operate, due to the significant standby loss. That's why a tankless heater saves 25% to 50% of net energy over a tank heater.
A heat pump can be more than 100% efficient, because they are a pump, not a heat source. This outweighs standby loss for many houses.
The other concern with on demand heaters is power use. An electric on demand is about the least green way to heat water, because the high power is likely to be supplied by gas turbine, and not base load generation.