Tankless WH for Radiant Heating?

Tom Hughes

Has anyone used a Tankless WH like Takagi or Aquastar for both radiant heating and domestic? Did you use a heat exchanger for the radiant? I'm in Santa Barbara and the water quality here is really poor. Can't have an open system for space heating.

kevin

Why would....

you want an open system for space heating anyway? I have heard of using them but it was not (and in my opinion nor should it) used for both the domestic and the space heating. If you want to use the tankless get a seperate unit for each use. There is no sence of risking you health for a few bucks. kpc

ta finnegan

Tankless applications

Go for an electric tankless like SEISCO. Watts Radiant now using them on their panels.

Definitely use separate system for the DHW.

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Brian (Tankless) Wood

I am plagiarising (sp)

here, but i think this combo system is the proprietary property of Alan forbes.

It's a 235,000btu T-M1. I'm sure he will fill you in on the details.

Brian in humid Swampland Wood.

Marc Sherby

tankless water heaters

Tankless electric water heaters are an excellent source for radiant when a boiler is nowhere to be found, such as additions when scorched air is being used in the rest of the house. In most instances especially slabs, the water temp. is well within the capacity of a tankless electric water heater. Many installers still use a standard inefficent 40 or 52 gallon electric to power these types of radiant jobs. They take up a lot of space, and are always heating that amount of water in the tank, whether there is a demand for it or not. Tankless heaters save considerably on both fuel costs and space. Siesco makes a really nice line of tankless electric water heaters and our company Radiant Heat Supply will be stocking them for radiant use.

Paul Rohrs_2

Pic's

Just completed an radiant floor job about 2 months ago with a Rinnai. It is working flawlessly. I had some initial concerns about the total head thru the heat exchanger. We only had 4 loops of 300' each but we piped it in 1" and used a 0011 circulator to account for the higher than average head. (25')

Art Pittaway

Just to be correct

if you wire and size it right a tank type electric or power vented gas HWH will only heat when there is a call for heat. Most power vented 40 gal can be wired so the tank heating will go cold if there is no call for heat. Electrics are even easier, just make sure you understand the control wiring before you do it.
Art

Paul Rohrs

Pics of heating install

This job finished about two months ago and is working flawlessly. We had 4 300ft loops but sized the heating loop in 1" to account for adequate flow thru the 12" heat exchanger. The head loss was at 25'of head so we used a 0011F taco and it really fit the bill. Even without insulation in this garage, it was maintaining 60F. The Homeowner was budgeting to add insulation for next year. (Crazy, I know.....)

PR

Tom Hughes

Rannai

Do you know which model that Rannai is? Is this unit also doing domestic HW?

hot_rod

Gee Paul

25'@ 8 gpm thru a 1/2" tube HX. Did you calculate the velocity? What is the life exceptancy of that tube bundle at that flow rate. Probably don't need much fire under it with that kind of friction. Talk about a cavitation invitation.

Needless to say I'm not a fan of this type of heater for hydronic applications. An 1/8 hp pump to move that load? Might as well use a forced air fan, probably less power consumption

hot rod

Tom Hughes

I know these tankless units have a high pressure drop. They're intended to be fed by city water pressure for domestic, not really intended for hydronic heating. What would you use instead? Munchkins are ideal but expensive. And tank type water heaters don't make any sense for hydronic heating. Electric doesn't work here because local energy codes forbid it for space heating.

hot_rod

You nailed it, Tom

they were designed for DHW applications. They should be left at that. So what, really, is the attraction? Size, price?

Remember, you get what you pay for, generally. So many good choices these day.

hot rod

Paul Rohrs

Max Flow

This Rinnai 2424W has a max flow of 6.2GPM and I must say It is working well.

The specifics:

1.Contractor became a certified installer of Rinnai products.
2.Contractors dad wanted 82% efficient and no standby loss
3. Contractor got an additional 50% for personal use.
4. Units has 10ea 18,000 btu burners that modulate. setpoint at 110F, return at 95F, the unit is purring like a kitten.

I was asked the other day by a friend of mine (radiant heat contractor) what I will put in my home when I build. My answer, Peerless CI. This job had a qualified installer telling me what he wanted. Rinnai makes a good product, there should be a buffer tank on this application, but budget overrulled my design.

Contractor, his dad, and garage are beneficiaries of a floor heat system that is efficient,functional, and affordable.

My hope is this contractor will work with me on future jobs when we can employ boilers, outdoor reset, constant flow as primary issues, and budgets as secondary issues.

PR

Jack_23

Rinnai for heating

Rinnai's are being used for Radiant, hydro-air and limited baseboard. The key to success is to understand (and pay attention to...or else) the formula:
GPM X Delta T X 500 = BTU.
As this is an on demand unit with a modulating gas valve (15K-180K btu)the unit will regulate its input depending upon the flow (which it reads) and the temp rise necessary. For space heating applications the most I've heard of them outputting was 120,000 btu and that was on a system with cascading temps (running 140 to an air handler and using the return water for the radiant). With the formula and the pressure drop you are not going to get much more than 5-6 gpm thru the unit with any reasonable size and cost circulator. For small radiant jobs, these are the balls. Insert your GPM and DT's and see how the numbers come out. Primary/secondary increases flexibility. TOTAL documentation is available at www.rinnai.us in the service tech section. Whether you choose to use these or not I will say this to all comers. In my 35+ yrs in the mechanical business, Rinnai has the most reliable products I've ever seen. Their technology is the most advanced in the gas products business. They have been making fully modulating gas valves, that work, since 1985

kevin

Paul...

you say that a buffer tank was out of the budget...A small 20-30 gallon electric water heater used ONLY as storage w/ a 007/8 wouldn't have been too pricey...and you could use the element ports for the 1" manifolds...were the $$$ margins that tight?
Looks like a neat job...what was the heat loss/btu req. for the slab? Did you use 1/2"pex?
Unless we try different ways of doing things we won't learn new stuff..trail and error if nothing is educational.kpc

kevin

A couple....

few ideas...Embassy/Cosmo gas makes a wall hung boiler/dhw boiler. Quietside boilers,Monitor MZ, NY Thermal has the Trinity...to name a few..kpc

Paul Rohrs

Rinnai Job

We used 12 Wirsbo Hepex for this job. It was my contractors first tubing install, so I ALWAYS insist on valved manifolds on the return. Inevitably, there are issues either with the system fill and air-locking it, or uneven loop lengths etc. BTU load was just shy of 20,000.

It was not something I would like to designsell as a norm. How can you not budget for insulation up front? I have to remember my job as a wholesaler is to give them what they want. Having said that......there is a point in time where I will walk away from a job knowing full well that my design will be piece-mealed out.

Latest job the HO took my design (Via the contractor) and bought his PEX at Menards.

The discussions about margins will have to wait, I will say that profit is a natural byproduct of a well run company, and margin is not a dirty word in my book.

PR

kevin

i missunderstood

your role in this job...I thought you did some of the installing. I did not realize you were the engineer/wholesaler... profit and margins are not bad words at all in any book. Gotta eat.kpc

Steve Eayrs

Rinnia for heating

I tried a few of these out this last year. Agree with some of whats said, but they are not a boiler! The efficiencies will never be as high as a boiler either, due to the way they short cycle, and other things. Of course that is partly due to having only LP here. I like them for a water heater, but too many problems for a heating system or a combination system.
The high head (25gpm) needed to operate right, can only be reasonably done with P/S, as far as I'm concerned. Also have had some strange howling noises, and vibrations. Did all the recommended changes and still have some problems.
If they could come up with a decent control for heating applications, that had a wider temp. range (adjustable hi-lo settings), they may have something here, but I'm sticking to boilers. A buffer tank could help here, but isn't the idea of using one, instead of a boiler to save some money? There aren't enough hours in a day to want to tinker with these to try to make it into a boiler. If you charged the customer for all the time tinkering, a boiler would be the better deal.
It better be a real small, very simple system, or in my opinion forget it. Doesn't take that long to pay the cost difference in a boiler system (w/ oil-fired Buderus, or similar option), w/ 50% more in operating cost for the Rinnai.
Steve