relay wiring help

rabradford1

I have a old house that froze last year (not because of me). 18 huge radiators cracked including the ancient boiler.
I have 2 fireplace that heated the house for 170 years and could do it today too but we are all less brutal then our forefathers. So I have installed 6 300ft loops of 1/2 tubing under the floor in the basement. all to a very nice manifold coming off a primary line. I have a Rannai 98 LSi tankless and a Taco bumble bee circulator. I also purchased a Taco SR503-4 switching relay. It will be a closed unit and I am satisfied if it takes the chill out of the floor and I still use the fireplaces until a future time when I can add to it and afford better ways to heat the home.
I have only 1 circulator that will feed the 6 loops. my question is when wiring the relay do I have to wire the Tankless to the relay and if so whats the best way. Or will my thermostat tell the circulator to move the water and the tankless automatically kick on? And do I need to have the temp sensors that came with the circulator installed on the feed and return lines of the manifold?

Harvey Ramer

This is from Rannai's Warranty info;
* Note:
Period of coverage is reduced to 3 years from date of purchase when used as a circulating water heater within a hot
water circulation loop, where the water heater is in series with a circulation system and all circulating water flows
through the water heater, and where an on-demand recirculation system is not incorporated.
On-demand recirculation is defined as a hot water recirculating loop or system that utilizes existing hot and cold lines
or a dedicated return line, and only activates when hot water is used. It can be activated by a push button, motion
sensor, or voice activation but not by a temperature sensor. A timer added to a standard recirculating pump is not
considered as on-demand.
There is no warranty coverage on product installed in a closed loop application, commonly associated with space
heating only applications.
Use of an MCC-91 controller in a residential dwelling will reduce the warranty coverage to that of a commercial
warranty application (except when an MCC-91 is used with a Rinnai Hydronic Air Handler).
The integrated controller on indoor models has a 1 year warranty on parts.


You would be very well served to return the Rannia and get a small boiler. This system is going to be trouble and it will remind you every winter. If you have family living with you in the house, they aren't going to be real proud of you either.

The Rannia you have is strictly for domestic water heating. A tankless water heater does not work properly for space heating.

Harvey

SherlockOhms

I had an apartment that used the water heater for heating using a small fan coil ,taco pump, transformer and Tstat.
it worked really well but in California winters are no too cold.

Ironman

As Harvey has so clearly pointed out, you have the wrong appliance for space heating. I know: it's a lot cheaper than a boiler. So is a coffe maker; but it won't heat your house.
A tankless is not designed, controlled or approved for space heating in spite of what some internet peddlers push. You now also see it has no warranty if you use it that way.
The BumbleBee also will not be able to overcome the high head of the tankless and move any substantial amount of water through it to the system.
Did you install heat transfer plates under the floor? If not, it will do well to emitt 1/2 the btu's it would with plates.
There's no way for the SR504 to signal the tankless to fire since it has no such connection.
Please get the correct appliance and we will be happy to give you guidance in getting it installed correctly.

Ironman

SherlockOhms said:

I had an apartment that used the water heater for heating using a small fan coil ,taco pump, transformer and Tstat.
it worked really well but in California winters are no too cold.

There's a big difference from a hydronic standpoint between a tankless and a tank water heater. Still, using a tank for both domestic and space heating is something that has been proven to be a bad idea and outlawed in most places. Think Legionella.

Zman

Hope you aren't discouraged by your first post here. Harvey and Bob are very knowledgeable and are absolutely correct.

The pipe sizing and configuration in your picture is dizzying. May I ask who provided the design?

If you are looking for some first hand information from a homeowner with a similar system you may want to read this post. http://forum.heatinghelp.com/discussion/152002/radiant-floor-heating-2800sqft-house#latest

You can send a message to the member if you want to discuss it with them directly.

Carl

rabradford1

I get dizzying. But very simple based on several at times wasted hours of research online and with hard books.
The tubing is 300ft each. They have fins , a radiant barrier , insulation and will likely be covered even further with plywood or Sheetrock.
Why is it some say using the tankless is a absolute no, and others say absolutely yes?
I guess at this point I don't care if it last more than 3 years and I don't care about the warranty. I don't have a choice other than to work with what I have.
So should I make a change on how the primary is set up? Can I just set a switch to manually turn the Bumblebee on and will that trigger the Rannai to start?
I need to make this work through this winter. It only needs to heat the floor up. I can use the fireplaces and a Toyo like propane stove to help heat the bulk of the air.
I guess I need to learn how to get the rannai to start in the closed system? And where to add the bumble bee t help push the water through the system?
Then this summer I can just replace with a boiler.
I left the red tube on the left available for adding it to a wood boiler that is in the basement about ten feet away from this set up. Would it be good to add the wood boiler or not?
like it or not, I listen to everyone opinion and appreciate it as well. I spent most of my life on a ship that required making what you have work . Please help me make this work?

Harvey Ramer

Well, I can't say that this one is a health hazard so...
Use the Taco relay to switch the pump on and off via the thermostat. Set your pump to speed 4 in the constant power mode. The Rannia has a flow switch that turns the burner on when flow is detected.

There it is.


You aren't going to be happy with it though and you will most assuredly ruin the Rannia. Whether it happens this year or next year I don't know.

rabradford1 said:

Why is it some say using the tankless is a absolute no, and others say absolutely yes?

The people who purport the use of Tankless on demand water heaters for space heating are nonprofessionals that do not have the experience or knowledge to design a properly functional safe hydronic heating system. They range from DY'ers, small builders and cheap skate contractors. They all think they invented something new. Most regret it and end up paying more they would have if they had done it right in the first place. I have seen more than one tankless get ripped out and replaced with a boiler. THAT'S EXPENSIVE!!!!

There you go. I helped you ruin your water heater. Shame on me!

At least add an air separator and put it under 20psi so you don't turn the water heater into a steamer if the high limit doesn't shut the burner down quick enough.

Ironman

rabradford1 said:

Why is it some say using the tankless is a absolute no, and others say absolutely yes?

Would it be good to add the wood boiler or not?
like it or not, I listen to everyone opinion and appreciate it as well. I spent most of my life on a ship that required making what you have work . Please help me make this work?

The two biggest functional problems with using a tankless:
1. Its heat exchanger is designed for an open loop with a lot of pressure pushing through it. In order to keep a 199k btu tankless from moving more than 5.3 gpm, the heat exchanger is intentionally designed with enough resistance to flow (head) to keep it in that range. It's designed for high head and high delta T (77*).
A closed loop hydronic system and its components ( boiler, pumps, piping, etc.) are designed for low head and low delta T (usually 20*). Hydronic circulators ( they're not pumps) are made for low head systems. They usually cannot overcome the head of the tankless and won't be able to produce enough flow through the tankless plus the system piping.

2. The controls on a tankless are designed to heat domestic water, not space heating. They activate the burner when a minimum flow rate is sensed and then tell the burner how much to fire based upon flow and temp rise through the heater (delta T).

Because the tankless is designed to have COLD (not WARM, not HOT, but COLD) water entering it; and because of its high head, when it's connected to space heating, it will have trouble firing at the correct rate, it will short cycle, not produce enough constant btu's and the HX will die of metal fatigue.

The only thing that you can do to get the thing running is to pipe it in correct primary/secondary to provide hydraulic separation between the heater and the system. Then put the BumbleBee on the system loop and use a large circ like a Grundfos UPS26-99 on the boiler loop.

It will still have issues, but that will give you some short term functionality.

A wood boiler with a tankless is probably the worst thing you could do to it unless the tankless could be isolated while the wood boiler is heating. You would need a mixing valve to limit the supply water temp to the floor in that scenario.

RobG

What do you mean when you say the tubing has fins? Is it under floor with plates or fin tube baseboard? Did you do a heat loss of the home? In my opinion your best bet would be to use the tankless heater for domestic hot water and install a boiler to heat the floor (you may need supplemental heat depending on the heat loss). You will end up throwing good money to bandage an axe wound when in the end you are going have to spend the money to do it right. The folks on this site will be happy to help you every step of the way.

On a side note, do they even make blue O2 barrier pex?