A Takagi for heating?

Unknown

You may or may not be a two temp system. If the bb and rads can be sized for lower temp operation, and a good thermostat used, you *might* be able to do this one temp, running slightly warmer water than needed in the slab.

If a takagi is a good choice, a tank heat is a better choice. In this case, a takagi is not a good choice; a mod/con would definitely pay for itself if you can size for low temp operation.

Gene Davis_2

Anybody used these?

A supplier is quoting us a complete package for heating a new house. Walkout basement lower level is infloor radiant, main floor above is all either radiators or baseboards. Total heat loss is about 44K Btu/h at -30F design temp.

With the in-slab radiant down and rads and baseboards up, we will be running a two temp system, at least.

Can one of the Takagi models handle this?

kevin coppinger_4

not advisable....

you would be using a unit not designed or certified/approved for that application....if it is for a client going back to replace it would not be a good thing....kpc

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PETE SKINNER

Check out Energy Kinetics EKpak go to www.energykinetics.com for info and yes it's a Takagi

Gene Davis_2

Not to be a contrarian at all. I'me not knowledgable about this stuff at all, but am trying to learn.

You mention "not designed," and "not certified for," in you post. By whom is it not designed or certified?

The manufacturer's installation instructions show settings and controls and diagrams for hydronic heating applications. What is going on here?

How does it differ greatly from the Argo and EFM electric boilers we've had contractors install in new construction homes here? (BTW, our electric rates are down around 3.6 cents.)

Ken_40

In many states...

a water heater cannot be used as a boiler. Other than from a blatantly obvious reason of "the designed end use and purpose of any product," A boiler must be ASME certified to be legally used as such.

Almost all products have a fundamental design purpose. To the best of my knowledge, water heaters are designed to be used as water heaters. This in no way suggests they cannot be used as boilers. But if I want a volley ball, why would I buy a basketball?

Frequently the use of water heaters as boilers is based on pure marketing, and the basic cost of water heaters generally being less than a true boiler (principally because they do not ASME standards). Then too, if you don't make any boilers, just water heaters, guess what the Sales Manager will suggest to all the troops?

And of course, always remember the Kps caveat:

"Great marketing will overcome mediocre engineering every time; typically in a ratio of 2:1"

JJ_4

Takagi

Contact Eric at Low Energy Systems, Denver, to see if they have done any systems with a Takagi as the heat source.

Mike T., Swampeast MO

Beyond certification issues, don't forget that "instant" domestic water heaters are designed around low flow and high temperature rise.

There are certainly similarities between such DHW heaters and some condensing/modulating boilers, but it's mainly superficial. Their "brains" in particular will be TOTALLY different. While the brain of a mod-con INCLUDES the ability to make DHW, the brain of an "instant" DHW heater won't include space heating.

Proceed with extreme caution.

Spudwrench

tankless for heat

Gene,
I have used a Takagi to heat my home since '04 with good results in a single temp sytem. As the others have said, it is not certified for boiler applications- which could cause all sorts of problems with insurance, building inspections, when it's time to sell the home, etc.
Having said that, it does cost under 1/3 of what a mod-con boiler does and can work effectively if the installer understands the limitations of the system. If you can afford a mod con, I'd advise going that way. More efficient, better service support, etc. I hope to upgrade to a mod con when finances permit.

Nathan

Plumdog_2

Seen it done

But it wasn't pretty. Poor old gentleman thought he had discovered a better, cheaper way to do radiant heat on an Internet site. He bought the package, and it wasn't as cheap as advertised when all the parts were there. The little heaters are great at converting 50 degree water to 110 degree water when you expect 3-4 gallons per minute for Domestic use. But when you try and circulate Heating fluids at 90-120 degrees in small gallons per minute, you are going to find severe design limitations with the controls and pumping and the way they interact. One time this guys house heated up to over 100 degrees, another time his pipes froze. Get yourself a real boiler with an indirect and stop trying to find a cheap way out. Or just go forced air with a water heater for domestic. Just my opinion.

Mike T., Swampeast MO

Exactly. The flow in a hydronic system can be WAY below or WAY above that expected by an "instant" DHW heater.

With very careful design and strict limits on control it can certainly work, but for the application you're thinking about, please choose a "real" boiler.

I know you're trying to keep things inexpensive but don't be cheap as your supposed customer buying this "simple" speculation off-season home both deserves and will want better.

Royboy

I've done a couple heating systems ...

using Takagi TK-Jrs. Both also did water heating - separated from heating with a HX. Part way through the 2nd one I was told by the Takagi distributor that I purchased from that they did not recommend using them (or any other gas on-demand water heater) for space heating. That the relatively low BTU demands for space heating results in running very throttled down which causes condensation in the heat exchangers and supposedly they rot out pretty quickly. The owner of the company said he had a Bosch unit (I think) in a heating mode in his house and they were monitoring it closely. Had the HX replaced a couple times already as I recall. They said that dual-purpose systems are better, because there would be at least periodic evaporating of the condensate during the water heating cycles.

Takagi does promote use for space heating apps (and warrants their HXs for 7 years) but the distributor felt the life span of the units would be shortened and that Takagi was more interested in upping sales than promoting good systems.

Me - don't really know. My systems have worked OK but I haven't gone back and dissembled them to look at HXs. I'm keeping my fingers crossed and would be hesitant to put in another like this without some better sense that it was OK.

Curious to read others thoughts on this as the water heaters are, as I understand them, pretty much small modulating boilers.

And one of our local utilities has real favorable off-peak electric rates and as a result, I've done several systems using on-demand electric water heaters by Seisco. Of course, no downside to running throttled down on those and they can be very cost-effective.

Roy

big willy

The same story

One time and one time only I built a system using a on emand water heater and I was very unhappy with the end result. If you are trying to get a modulating high effeciancy machine for less keep this in mind. A on demand heater is capableof as high as 86% thermal effeciancy but, this is with incomondg water temps of 40-55 deg. in a hydronic system the heater will see incoming temps that are more like 80-140 deg depending on the system type. This greatly reduces the effeciancy of the heater. Also the heat exchanger will not last as long the first pass in the water curcuit is designed to absorb tons of btu. This would be the cold incoming water. If the incoming water is high temp already the heat exchanger runs far hotter than its designed
for. I have seen a lot of on demands loose there heat exchanger early because of this.

Plumdog_2

Another thing

Tankless heaters are activated by flow and the burner is regulated by temperature sensors, on the inlet and outlet. The 3/4 inch inlet sees 50 lbs or so of static water pressure. When water is drawn at the outlet, you have 50 lbs pushing thru to the outlet, which is restricted only by friction, length, and head. If you try to circulate thru that heat exchanger with pumps, you are facing a severe uphill battle. Furthermore, a real boiler comes equipped with wiring designed for it's intended purpose, and it can be controlled easily and works like a miracle.

Plumdog_2

Ingeniuos no doubt

The burner and microchip the operates it is really quite clever; but it is intended to heat domestic water for showers, etc. and nothing more. You can have a bad time trying to trick the unit into heating space heating fluids that are slowly circulating. Any of the mod-cons, however, have outdoor reset, domestic priority, pump switching, proper safety chain, and a host of other features that make them way more desirable for heating and domestic hot water production. And most of them are legal.

Spudwrench

A number of folks have made comments to the effect of "a tankless is not designed to handle the wide range of flow rates in a heating system." I find this puzzling- perhaps I am wrong here, but if you pipe it P/S, isn't the flow in the primary loop constant whenever the circulator is running? In a single zone non P/S system, the flow rate is also constant unless you are using TRVs or something. Furthermore, per the spec sheets, the Takagi Tk jr. is good for anything from .75GPM though 5.8 gpm. So, at a 20 degree delta T, you're not going to be able to get more than 58K btu out of it.
Takagi shows domestic heat applications in their installation manual. Given that the unit has a 7 year warranty on the HX, why would they encourage an application which "causes premature HX failure."
To my mind, the most valid arguments against using a Takagi as a boiler are: lower efficiency compared to a mod-con, code/insurance/resale issues, and the fact that it can't flow more than 58K btu.
Nathan

Plumdog_2

Another valid argument

against using tankless heaters for space heating applications is that they modulate around flow rate and in/out temp to achieve a fixed output. That fixed output doesn't lend itself to controlling your circulating fluid temperatures as need dictates (outdoor temps).