Indirect vs Instantaneous hwh

Tom Befford,Scott Technical Service

Don't forget Kevin...

BTU is the sensible heat required to raise 1 pound of fresh water 1 degree F.

A gallon of fresh water weighs 8.33 pounds.

tom

Steve-O

Indirect vs Instantaneous hwh

Installed many indirect hwh. Am getting alot of customers requesting Instantaneous hwh because they claim to give you endless hot water.Any pros and cons to either one?If these instant hwh's are so great how come every one is not using them ! Still hear alot of talk about indirect being a great way to heat hot water?Is this false advertisement or fact?

kevin coppinger_4

it's a little...

bit of both! Watch those ratings! most of so called endless supply comes from pretty high entering water temps..great if you live in Fla. not so hoit if you live in New england where 40F well water is not unusual....It is endless so long as you don't out run the GPM...What are the needs...compare what are the expectancy of their hot water is do they want to do laundry, take two showers and wash dishes at the same time...you may need more than 1 unit to get that done....kpc

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Kevin__Flynn

hot water

Look, it's not magic. It takes 1 BTU to raise 8.33 gallons of water 1 degree Farenheit.

So, if the required GPM's are able to be handled by the BTU's produced by the instantaneous heater, there's no problem.

The benefit of these heaters are that they only heat water when there is a draw, so there is no off cycle losses. Some units even have modulating gas valves so lower inputs are utilized when only one fixture is in use.

The downsides are that they have small heat exchangers, so if there are any water issues (hard water, well water. etc...) clogged or failed heat exchangers could be a problem. The greatest downfall is that there is no storage. Often, even in homes, there are large dump load requirements. It is not uncommon to find shower set-ups with 25 GPM + requirements. To handle this with instantaneous heaters would require nearly a million BTU's/hr output. When using an indirect heater it is possible to offset the BTU requirements with more storage. And these days most indirects are so well insulated that there isn't much concern about off cycle losses. Some even allow access to the tank for cleaning.

Hope this provides some food for thougt.

Kevin Flynn

Tom_35

Has anyone

used the electric instanteneous water heaters? These things are incredibly small but they claim they can take care of a 3 bedroom/2 bath home.

Tom Atchley

Scott Gregg

Tankless Heaters

Electric’s fine for 3-bath house? I think it's a stretch at best. The best electric tankless out there only gives about 4 GPM at it’s best. Most of the decent gas models do this at their worst.

IMHO a couple of pro’s to the indirect are you already have the boiler to make the hot water and it’s already running for half the year giving reduced hot water costs. Another is the fact that most are lifetime warranty. No flame no flue makes them last virtually forever. Sized correctly in a house with even the extreme fixtures we are seeing they work great and you won’t run out of hot water.

Before we get too hung up on the flow rates required of plumbing fixtures we have to understand a few things. Just because a fixture is rated at a given GPM does not mean that is what is uses in the real world. Case in point; a 2.5GPM showerhead rarely gives 2.5GPM in a home! Most of the time it runs around 1.5 GPM or less! Every foot of pipe and fitting and valve has a pressure drop that is not figured under the lab conditions to rate a fixture. All you have to do to refute this is to stop guessing and MEASURE the flow in the field. Having done so for the last couple of years studying tankless heaters has taught me a lot. Also remember that most of today’s homes are piped with a ¾” PEX or CPVC hot water main. With the system looses, you are not going to be able to get more than about 10GPM to anything in that house. (again…measure it sometime) One more thing if it’s a well house. Most well pumps in homes or 10-12 GPM max. (Talking averages of course)

I have yet to see a home with a Noritz or Rennai in it that had a “too low a flow rate” issue. I also have yet to see a home with a well or hard water that had problems caused by it in a tankless heater. Not that it won’t happen, I just have not seen it anywhere but in the bogus test run by a certain tank company comparing the two products.

Both indirect and tankless heaters are a great choice for domestic hot water. I would be happy to have or recommend either of them. If a home had an extreme fixture (10GPM or more) I would go tankless every time. A twin or multi-system tankless approach to this need is really hard to beat with anything else. If you can afford such a fixture, you can afford the system required to feed it enough hot water.

Al Corelli

I use an early Bosch in my house. Great for two people. Only one fixture at a time (and we have a static pressure of 120lbs.)

I love it. I will update it to a pilotless unit when this one fails.

Kevin__Flynn

OK Tom

where did I go wrong, other than doing the math for everyone.

Kevin Flynn

Tom_35

electric instanteous

Thanks Scott,

I figured that it would be a stretch with an electric, but have never talked to anyone that had any experience with the electrics. I have a customer that is building a new home that natural gas is not available and he doesn't want propane. Oil is not used in our area, so electric is his only choice.

He was thinking about one of the electrics for the "guest" end of his home that consists of 2 bedrooms and 1 bath. I told him I would check with guys from The Wall and get back to him.

I figured that it might also be an issue with entering water temps during the winter as well.

Thanks again,

Tom Atchley

Joe Brix

A combination

of electric HW heater with an instant might be your only solution. I think you're gonna need over 150 amps of power just to run the two.

Kevin__Flynn

Tom, I am embarrassed!

I finally see my error. I must have had a bit of a brain cramp.

Thank you for pointing this out. Allow me to correct;

"Look, it's not magic. It take 8.33 BTU's to raise 1 gallon of water 1 degree Farenheit."

Thanks again,


Kevin Flynn

Tom Befford,Scott Technical Service

brain cramps

I get them all the time...why just yesterday...#$%&*&%$#$(*&^%$@$%...
tom

hr

You can buy as much

electric horse power as you can gas fired, when it comes to DHW production.

I have seen hotels running with electric hot water generators connected to 1000 amp breakers! Even swimming pool heaters are available in electric.

Just use the KW to BTU/ hr multiplier to understand how many KWs you need to supply to get the job done, if BTU/hr is the number you are most comfortable with.

The water really doesn't care what fuel source is adding energy to it. I agree many homes probably do not have the spare amperage to run high gpm production,electric instantanous heaters.

hot rod

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Tom Befford,Scott Technical Service

energy costs

ultimately the customer pays the energy bill so what works best is what delivers the most economical BTU's. I live on Vancouver Island, BC. Values are rounded up to the next cent.
Electricity..... $.18 per ton NRE (12,000 Btu's);
Natural gas..... $.14 per ton;
Fuel Oil..... $.20 per ton;
Heat Pump..... $.12 per ton;

I put the electric-powered air-to-air heat pump on the list. In this temperate area, it is the least expensive option to heat a home, given the efficiency of refrigeration. Installation cost is generally 50% more but the payback is about 4/5 years depending on heat requirements and setback times. And most people end up using the air conditioning side of their appliance. In most areas the area is too rocky for ground source otherwise the efficiency would be greater. Some schools use their playing fields and parking lots for a buried ground loop.

Tom

Nron_13

solar storage

lot at solar storage tanks to help ajust the temp and use the electric heater as a boost for the last few Btus required

Scott Gregg

I like that idea!

I like the thought of this a lot! If you can feed that electric tankless (most good 120amp units) anything over 80* water, you will get a flow capacity about equal to most gas tankless fed cold water. And it will use less juice to get you there.

You guys are going make me learn about solar now?! That's going to make me mad and I'm going to be in anger management with Dave Yates.

Doug_32

instant v. storage

Unless the homeowner has a generator, the other advantage of mating an indirect with a high-efficiency boiler (rather than using combi units or point-of-use instants) is that when the power goes out, your customer still has hot water (until the tank runs out)...........

Tim_24

Recirculation

Not really a good way to recirculate an instantaneous system, as far as I know. Always nice to have hot water at the fixture within a few seconds of turning it on.