Tankless Water Heater vs. Boiler for Radiant Heat

Plumdog_2

Arlie; I tried to help out a guy that bought a tankless radiant heat project on the internet because he thought it looked and sounded good. It was too good. There is no good way to control these things for heating purposes, the burners are a marvel of technology but the electronics won't interface with the stuff that you need to do a good heating system.

Arlie Campbell

I'm in the process of building a new house - planning stage. I'm going to put in radiant floor heating and every site I've visited wants to sell me a boiler and discourages the use of on-demand water heaters. I'm currently using a Toyotomi kerosene water heater rated at 148,000 btu's. What I need is a good explanation of why I can't use an on-demand water heater instead of a boiler. The boilers I've seen on the radiant heating sites are much more expensive than the on-demand I'm using now. Thanks for any help.

Mike Thomas_2

Alwlays a Reason

What are you using the on demand water heater for now? If it is just for heating water, you are probably happy with it. But just remember, that demand water heater was designed to to take 45-55 degree water and boost it to say 110 to 120 water. About a 55 - 60 degree difference.. It was designed to do that, and operates very efficiently. In a radiant floor application the heating source supplies water temperatures with only a 20 degree difference, supply and return. Only a boiler can do that efficiently. Now, if you think that all those engineers and guys like us, who design, recommend and install boilers, instead of demand water heaters, really don't know what we are talking about, or have never tried it, or maybe it is just a conspiracy to keep selling those expensive boilers, go ahead and design your own system. You will learn your lesson like many before you. There is always a reason, why things just cost so much.

Simply Rad_2

Hey Mike

Well put Mike I would buy a radiant system from you
Jeffrey

Bruce M.

Toyotomi

The Toyotomi has a maximum water temperature of 155 and is often used for radian heating. I was told that the company is in the process of having it rated as a boiler.

Paul Malko

148kBTU/hr?

If you want to save money on the heating system, reduce the heat loss of the house. I'm getting heat and hot water from an 80kBTU/hr heat source and I'm sure it is too big. Should have gone with the 50kBTU/hr model. Total heat loss is 24kBTU/hr at -10degF design temp for a 1500 ft^2 house in VT.

I agree with these guys, an on demand hot water heater will have a shortened life and lower efficiency if forced low temp rise heating strategy. As an engineer, please use devices for what the designers intended.

Scott Gregg

As good a reason as any

Here is one. If you use a tankless as a boiler the warranty will drop drastically from about 10 years on the heat exchanger to 3. It seams, they know something about it.

That said, it is a cheap BTU! They function similar to the Muchkins and copper fin boilers.You might be able to pay for two tankless v/s one 90+ boiler of the same BTU rating.

I really like tankless but I still say boilers are boilers and water heaters are water heaters.

Alan(CaliforniaRadiant)Forbes

Two reasons

1) On-demand water heaters have very high pressure drops through their heat exchangers which means that you have to use a high-head pump which costs more to operate and can be noisy.

2) Most on-demand water heaters are 80% efficient where boilers are available to operate at greater than 95% efficiency.

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joel_19

Yup

I can use a Chainsaw to rough the ductwork into your house too but that's not a great idea. "Don't wonder if you could worry about if you should"

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Bruce M.

Greater than 95% Efficeiency?

> 1) On-demand water heaters have very high

> pressure drops through their heat exchangers

> which means that you have to use a high-head pump

> which costs more to operate and can be

> noisy.

>

> 2) Most on-demand water heaters are 80%

> efficient where boilers are available to operate

> at greater than 95% efficiency.

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 53&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Bruce M.

Greater than 95% Efficeiency?

The Toyotomi has an 88% efficiency rating and weighs 86 lbs. Please tell me which boiler has a greater than 95% efficiency.

Bruce M.

Toyotomi Specifications

Water Flow Rate/
Temperature Rise: 6.1 gal./min. (40°F rise)
4.8 gal./min. (50°F rise)
4.0 gal./min. (60°F rise)
3.5 gal./min. (70°F rise)
3.0 gal./min. (80°F rise)

I have talked with a Toyotomi distributor who sells many of these on demand water heaters for radiant installations in a very cold area of the country and they do an excellent job at heating and save a lot of money on operating costs. In addition they are able to operate on kerosene and number 1 and number 2 fuel oil.

Constantin

With the right return water temps...

... a Munchkin, Vitodens, Ultra, Trinity, etc. will all reach up to 96% efficiency. The AFUE test is done with a 140°F supply, so there isn't a lot of condensation going on at those temperatures.

Besides, there is far more to efficiency than just the AFUE. For example, the ability of modern gas boilers to modulate down is what made Mike T. save 44% on his gas consumption on a DD-corrected basis.

Bruce M.

Efficiency Comparisons

The Toyotomi is oil-fired but I believe you are giving me gas-fired efficiencies of for example, 96% on a Muchkin. The Ultra is also gas-fired and has a 92% efficiency and 98% in low-temperature applications. I believe that if we are making comparisons we need to compare only oil-fired equipment.

GH

97%

MONITOR / www.MZboiler.com GCSRADHEAT.COM if you want radiant right and if you want to be the installer and
get quality with performance . YEA I would use a boiler
or hundredes of millions of people are heating houses
wrong.

Constantin

My apologies...

With those efficiency numbers, I thought you were referring to the gas side of the business. The only condensing oil boiler currently approved for sale across the US is the Monitor FCX. The FCX makes it up to 95-96% efficiency, BTW.

To achieve the same output as your current heater, you'd have to buy two FCX's, and that could get pretty darn expensive. So, I'd look into getting the house insulated well and then size the heater/boiler to meet that need. We're achieving 5.1BTU/(ft² x degree-day) with an old house in Boston and new construction can go a lot tighter than that with only a nominal increase in cost. Then, a single FCX can do the job of heating the home and providing hot water at the same time.

For an excellent near-condensing boiler, consider the Vitola from Viessmann. One wallie claims his makes it to 90% AFUE when running on a low-temp radiant system, and the Vitola is pretty bulletproof, legal for sale across the US, and comes with a nifty control system as well. Naturally, it ain't cheap.

If your Toyotomi hot water heater ever gets rated as a boiler in your area (i.e. legal for install), by all means, go for it. However, I too have my doubts about the heat exchanger life and would recommend a buffer tank in the system loop as well as in the DWH system, to prevent short cycling during the shoulder months.

Mad Dog_2

I agree Mike

No free lunch! Mad Dog

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Plumdog_2

poor dude

Arlie; I tried to help out a guy that bought a tankless radiant heat project on the internet because he thought it looked and sounded good. It was too good. There is no good way to control these things for heating purposes, the burners are a marvel of technology but the electronics won't interface with the stuff that you need to do a good heating system.

Mark Eatherton1

What Mike said...

Listen to the voice of experience, and ignore your gut feelings. Just because they both heat water, there IS a big difference in their design and operation.

Some people will say anything to get you to use their products in a range they "think" it "should" work OK in.

It works somewhat OK, if you don't mind major short cycle operation. Short cycling is guaranteed early death for any piece of mechanical equipment. In my 30+ years of experience, I've not seen ONE mis-applied DHW heater being used as a space heater that didn't need to be replaced with a real heating appliance.

In addition to the mechanical problems associated with this type of operation, there is also the negative health impacts associated with water bourne diseases if the appliance is going to serve dual purpose without the use of an isolation heat exchanger.

As a licensed master plumber/hydronic heating contractor with over 30 years of experience, I can not recommend this application, regardless of what the manufacturers tell you...

ME

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Bruce M.

Mark

With all due respect to your 30 years of experience, I do not believe any of that includes an oil-fired on demand hot water heater. That piece of equipment is often short-cycled and is capable of continuous operation as well. I love old technology but I also admire the inventiveness and the ability to produce quality equipment in Japan and Europe. I am convinced that the high price of fuel oil has driven them to excel in this area. Just think of the list of top quality manufacturers that are not made in the US.

Unknown

if short cycling is a problem.. use a buffer tank. eats up a little of the cost savings, of course.

Let me say I am not advocating on-demand water heaters for all apps in preference over high-efficiency boilers! But they can be made workable and sometimes, you can't always have what is best.

Also, not all units are created equal. Five years ago you'd be hard pressed to find an on-demand a manufacturer would stand behind in a radiant application. These days, there are at least a few out there that are specifically shown in radiant applications in the manufacturer's tech lit.

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Mark Eatherton1

You are correct Bruce...

I have three oil boilers that I've installed and I did NOTHING wih the burner apperatus on those appliances. However, my gas experience covers the gamut of all burner technologies in that field, from non modulating to fully modulating, condensing, non condensing and partially condensing appliances.

You are also correct that the American manufacturers are being left in the dust when it comes to efficient combustion technology. It makes me sad to have to go outside our borders to try and get the most efficient, reliable equipment there is. And trust me, I've looked at the American version of high efficiency equipment (what little there is out there) and I must say, I'm not impressed with the menu.

Many have tried (GloCore, Burnham, Dunkirk etc.) but they fall way short of the competition from outside our borders, above and below the equator. And times, they are a changin'. Maybe the Japanes have learned the German's secrets as it pertains to flame modulation, but one thing for certain, if it's a high pressure drop coil, which they all are, it wil still require an extraction pump with extremely large cajones to make it "work".

As Rob said, you can add mass and make them work, but at what expense...

And don't get me wrong, I'm not one of your cigar chewin' soot covered boilermen from days long gone. I used to have a gas fired instantaneous tankless water heater serving my home, and it worked wonderfully, provided that we worked around it's limitations. I believe there is a right application for just about anything out there. I just don't believe that they should be misapplied just to get the manufacturers a larger chunk of the "hydronic pie". If they want a piece of the pie, they should redesign their appliance to conform to the needs of the industry, not viceaversa.

JMPO

ME

By the by, what's your background and experience dictate?

ME

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Bruce M.

My early experience

was on coal fired low-pressure steam and coal-fired hot water heaters. I loved coal, the warm glow of the fire, the incredible heat but I also remember cleaning out the cinders and clinkers, shaking down the grates, shoveling coal and the imprecise control system for regulating heat. I went to boiler school in the US Army in the 60's and almost everything we had was coal fired. I learned oil burners but I do not know gas-fired equipment other than some water heaters. You are absolutely correct about the lack of innovation and advanced technology in the American manufacturers. They remind me of the American automobile manufacturing industry that is losing more and more share of the market because they make what they have always made for the most part. I believe that the current price of fuel oil may just be the catalyst to spur the American manufacturers to design something that is new technology but I would not bet too much money that they will do it. Let me share an old Army saying for you; "If you do what you have always done, you will get what you have always got."