Tankless hot water heater for in floor radient heat?

Constantin

much of the calculation is pretty simple. You have a delta in the initial year (zero), followed by gas savings every year. You determine how much gas the condenser will conserve and then speculate on the CAGR of the gas prices to suit, as well as the investment rate you want to use for the NPV calc... I used 5%, which is pretty close to the risk-free rate available for consumers at the time.

BTW, I would not assign different service costs, as any combustion appliance ought to be serviced annually. It is doubtful that the life of a tankless will be as long as that of a quality boiler, IMO, but put in any life you want and see how much the future cost will impact your calculation... the higher the investment rate, the less events in the future will be of interest.

James_13

Tankless hot water heater for in floor radient heat?

I have a small area to heat. About 1200 square feet. I'm looking to put a small tankless hot water heater for the infloor heating. Any problems or issues with this?

The 2 models are the Bosch Aquastar 125B and the Rheem Encore 4.2.

I think it would save space and energy.

Thanks for your input.

James Schwalbach
Hartford, WI

PM_2

Boilers vs hot water heaters

The pros to using this approach are: 1)the heat source is cheap and compact, 2) see 1 above

The cons are: 1)the design life of hot water heaters typically is less than half of that for boilers (5-7 years vs 20+ years), 2)the efficiency is lower than a modern boiler, particularly if it is condensing.

If the goal is cheap heat this is fine, but not on my jobs. Disposable heat sources worry me and fuel isn't getting any cheaper.

Terry

tank

Even the tankless manufacturers recommend a buffer tank for these as they will cycle EVERYTIME there is a call (even small ones).

Adding a tank makes this a glorified Water Heater (no longer "tankless").

I'd use a Wall Mount Condensing Boiler dialed to required floor temp. Now your saving space.

As for Saving $$$. If your gonna go thru 2-3 of these units and add in instalation costs for each. Your better off paying more now.

jmho
EIN

bb

DHW

Would you be using the tankless heater for DHW as well? If so, you should isolate the radiant from the DHW to prevent legonella!

Also, you may have a problem w/ supplying DHW when swithcing from radiant... the return from the radiat will be much higher than the supply temp from the street. It will take the heater a little while to accomidate the change. May also need a flow switch for priority...

bb

Jim_65

Great advice!

There are way too many of the tankless heaters are being installed in the wrong applications. For some reason people think this is the solve all to every application. It is very reassuring that some are not willing to comprimise to installing cheaper systems that are incorrect and will cost much more in the long run.

joel_19

no

no , period , done end of story . 1200 sqft isn't that small just buy a boiler .

Spudwrench

tankless for radiant

Jim,
I have used a Takagi tankless (model TK-jr) to heat some panel radiators with pretty good results in my 1200 Sq ft. home. It will not be as efficient as a condensing boiler of course, may not be code approved for this application, but IMHO, offers good value for the money. Service life is an arguable point, but for the price you can buy several tankless units for what you'd pay for one boiler. I think that the Bosch 125 uses a mechanical modulation device for the burner (not sure) and think you might be better off with an electronically modulated tankless unit like the Takagi- you can program what output temp you want and away you go...it will simmer down to as low as 25K (?) btus if needed. As another side note- it is a bit noisy, take care to size your pumps correctly if you go this route, and don't go this route if you are planning on selling your home shortly as buyers/home inspectors may frown on it. Good luck!

Nathan

Scott Gregg

Here we go again

I am NOT a Bosch or Rheem fan. (My opinion of the Bosch is pretty low and I'll leave it at that) I do like Noritz (Personal favorite) and Rennai and Takagi. These are the "big 3" for tankless worldwide. They WILL work. They WILL save you "up-front" cost. You can buy 2 for about the same price as one boiler. You will get (With the better models) full modulation. This helps in the economy of your system.

The jury is still out on how long they will last. I have seen some pretty wild stuff with the things in the last 3 years. No, it's not the last 20 years, but heck, at half price for full modulation, why not try it on price sensitive jobs? If you get 10 years out of it, you're money ahead!

The good tankless water heaters are really not much different than the copper fin boilers or the Munchkin/Pinnalce in operation. (Other than the condensing part for munchies)

I would loose no sleep in installing one in this application. As mentioned, do NOT use it for a combo system without designing to protect against legionella. If your radiant sytstem runs at 120* or better you're going to be ok.

singh

BOSCH Aquastar 125B

is not approved by manufacturer to be used in heating applications.
It won't perform well and they wont warranty it.
spend the extra 1500.00 over a tankless and buy the BOSCH/Buderus GB 142/24.
At 98% eff. it won't be long before you re coup the extra costs.

Constantin

I'd stick to the boiler...

... there are some tankless water heaters that are rated for heating use, and in some areas, it's even legal to install them for that purpose, just as it's legal to have open-systems in some areas. Yet, would I do it?

No.

IMO, the downsides to using a heater that is designed to run a couple of hours a day on a 24/7 basis are far greater than using a boiler that was designed for its intended application. Some tankless units are perhaps more robust than others, but between the high-head losses and the complications you'll encounter if you want to heat your DWH and the house, I'd spend the extra on the materials and get a boiler.

If the house is occupied year-round and your gas prices are as high or rising as quickly as mine, you'll probably recoup the investment in a couple of years. A simple NPV calculation will tell you that story.

Dale

Load?

You may want figure the load first. If the 1200 sq. ft is pretty well insulated, needs maybe 30K, I think the tankless like the Rinnai commercial( same as residential but approved for in floor heat) work well and at 82% effecient are reasonable. There are alot of them in Wisc. but I would want a local firm to do the install, not complex at all but someone needs to work with the wholesaler. Johnstone supply in Madison and Milw. As to life, 5 yr warranty I think, but likely to last alot longer. I have heard nothing but good comments on their tech support.

Tim_24

I use a \"surplus\"

Aquastar to heat my garage, which is done by imbedded tubing. Despite what some have posted here, it works quite well. I have had it inservice longer than the warranty, so that is not a concern. "Rated for comfort heat use" it is not, nor is it my primary source of heat. It is not very thermally efficient. It does make hot water in a compact package with no possibility of being "shocked". Very simple system. LV stat starts the pump, unit fires on its own flow switch input, unit modulates to maintain a manually set outlet temperature. Very consistent heat. Aside from the possibility of reduced longevity (which is counter to my experience) and the lower efficiency I can see no reason to use this means as a supplementary source of heat.

On the other hand, had I not used a "leftover" unit for this purpose, I would not have purchased one as a "cheap boiler". Your use and intent is what you should base your choice on. If the comfort of my living spaces depended on the unit, any water heater, tankless or not, wouldn't have been an option. For my garage, not critical (but nice).

[Deleted User]

just check with the status of their approval application

:-(

Paul Cooke

Tankless

Have been rethinking the use of these tankless heaters lately.

Here's a couple of examples:

Two weeks ago I had a heat exchanger fail on a Rinnai that was installed in 2001. Still under warranty, they sent out a new one. It took over 2 hours to replace it. It was hard to charge the customer for the time it took to replace the exchanger, as well as the time it took to remove and reinstall the heater. This one was used to heat a very small home (closed loop).

Two days ago a Rinnai commercial indoor unit started leaking. This one was serving a commercial kitchen. It was installed in June of 2002, so it lasted about 3 and a half years before the heat exchanger started leaking. They were without hot water for about a day. I had to get a new one so they could get their hot water back asap. Rinnai sent out a replacement exchanger which I will install in the other heater, so I guess we'll now have a spare unit for the next time it fails.

(On a side note, this same heater required two service calls recently because of a buildup of lime on the heat exchanger. When you factor in service calls for these things, how much are they really saving?)

I want to like these heaters....but it's geting harder for me to suggest that people choose them over a standard tank type heater.

Dave Yates (PAH)

It might

be velly interesting for you (those of you who think a tankless will save money in the long run because it's cheaper to purchase) to actually sit down and determine the life cycle costs associated with a tankless versus a condensing modulating high eff boiler. Ignoring all of the other issues and concentrating on a truer reflection of costs will be a real eye opener.



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John Van

Life cycle costs

As a homeowner, I would like to do just that. Can you give me some guidelines to calculate the total life cycle cost of a high efficiency, condensing, modulating boiler? I can get quotes on the installation costs and I can calculate fuel costs. What about life expectancy, maintenance interval (i.e. service expenses), etc?

Josh_7

Tankless failures

Anyone else have any failures with Rinnai or Takagi water heaters?

Matt Connolly

Do it once, correctly

I have had a Monitor MZ 25 in my house for 7 years now. It heats the radiant floor of 3000sf, makes the dhw, heats the garage radiant, and heats the pool in the summer. It is wall mounted, about the size of a medicine cabinet, and 95% efficient. Why mess around with a water heater when you can have a bullet proof condensing boiler? It does cost more up front - but actually cost less over time. I have yet to service the thing. I will wait till it stops working, which could be a few more years. If you are going to be in the quality heating business you must represent quality - not cheap shortcuts. go to www.mzboiler.com to learn more. ( I was the sales manager for 5 years for the company. I chose to work for them after installing the unit in my new house.) You will never regret the choice.
Matt

Josh_7

Tankless

One of the problems with these heaters is that it's near impossible to get in there to clean out the incredibly small air side of the heat exchanger. Once some condensate or crud or dirt or whatever gets in there the restriction just compounds.

They make these things so compact, service is a problem.

Mad Dog_2

I'm with you matt

there is NO free lunch - period! Pay now or pay later. I wouldn't assume he's a heating contractor either. MD

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