In last week’s “Toasty Tootsies” post I went over the way our In Floor Heating system works and concluded my explanation with what I thought was a rhetorical question;

“Brilliantly simple don’t you think??!!

Well, based on the number of comments and Emails I received, while our In Floor Heating system might indeed be “Brilliantly Simple” my explanation was NOT!  Therefore, let me try and mend this by revisiting our In Floor Heating and do my best to improve my explanation of how this Open Direct type of system works.  If I’m successful I think that most of you will come to agree with my assessment that this Open Direct system is indeed “Brilliantly Simple”! 

But you will be the judge of that and so Please do add your comments as to how well this second attempt helps you to understand how our In Floor and Domestic Hot Water systems work and don’t hesitate to add your additional questions and things that still don’t make sense to you.

OK, here is my second attempt to show how this all works;

Deeper Dive into our Open Direct System;

One of the Emails I received, (thanks Benjamin), asked the following set of questions that included many of the points of confusion others sent me so I thought I’d use this to frame this expanded explanation of the Open Direct system I used to design our In Floor Heating or IFH and Domestic Hot Water or DHW System.

Benjamin wrote:

If I understood your installation diagram correctly, you run the drinking water through the same pipes as the water for the underfloor heating. Drinking water and “heating water” are identical, or not installed separately. First of all, this is economical because you one water circuit less. But I have a question about summer operation: drinking water and heating are usually installed separately, because in summer mode

  1. you want to avoid hot water flowing through the heating system, and
  2. the water should not stand still in parts of the circuit for a longer period of time to prevent the formation of legionella.

You can probably avoid point a. with valves that separate the entire heating circuit from the drinking water circuit in summer. But if the heating circuit is not flushed for several months during summer operation, legionella can form and then be flushed into the drinking water circuit when the heating system is put into operation. How do you avoid this? Is the underfloor heating completely drained during summer operation modus?

Thank you very much for further information!

First, let me try to resolve some common sources of misunderstanding that Benjamin and many of you mentioned;

I should have emphasized more how the various parts of our overall water systems are separated from each other.  In last week’s post I mostly left out the Cold or “drinking” water system so it needs to be understood that this has its own set of plumbing and ALL the water we drink and cook with comes directly from the water tanks to the cold water taps/showers onboard.  All the water in our water tanks comes directly from the onboard watermaker so it is as clean and close to pure H2O as is possible.

One of the things that seems to confuse many people at first is to understand that there are only TWO conditions that causes water to FLOW in a plumbing system:

  1. The regular water pressure in the system causes water to flow IF and ONLY IF water is being REMOVED from the system.
  2. There is a continuous circulation loop with its own PUMP that causes water to flow round and round through the CIRCULATION loop.

When neither 1 or 2 is true, there is NO FLOW of water through the plumbing. 

The Hot/Warm systems are the ones based on the Open/Direct system on Möbius and this has TWO different but interconnected systems:

  1. The In Floor Heating Mode which provides WARM water to heat floors when wanted.
  2. The DHW Domestic Hot Water Mode which provides HOT water to all the sinks and showers at all times.

I have modified the following illustrations from last week’s post to show a clearer picture of how these two systems work.

Open Direct HEATING Mode illustrationWhen no Hot water tap is open there is NO Cold water entering the system.  However, when one of  the In Floor thermostats turns on a Zone Circulation Pump, warm water then flows out of the Calorifier, through the in floor PEX tubing and back into the Calorifier.  This is a continuous loop so warm water is flowing through the floor tubing anytime the circulation pump is running.

Open Direct DHW Mode illustrationThe DHW system always takes priority so whenever a Hot water tap is opened, the system works like this in DHW Mode.  When any HOT water outlet at a sink or shower is opened, the regular pressure in the Cold water system which runs about 60 PSI, causes Cold water to enter and flow through the PEX tubing in the floors to refill the hot water that has been removed from the Calorifier.
Open Direct with DHW Circulation Loop schematicWhen the Hot water tap is closed the system automatically reverts back to In Floor Heating Mode and the Circulation Pump causes Warm water to circulate though the floor and keep it toasty warm.
To answer another question I received and as should now make sense, we do not actually “drink” water going through the DHW or In Floor Heating, though there would be no problems if we did.

It can initially be a bit confusing because when Hot water is consumed (taken out of the Calorifier by turning on the hot water at a sink or shower) and the system is in DHW mode as per above, it is necessary to replace the water that has been removed from the Calorifier so Cold “drinking water” does enter the DHW system.  This is exactly the same as in ANY home or other setup with a Water Heater or Calorifier; when Hot water is taken out, it must be replaced with water from the Cold water supply.

In operation this works extremely well and does so automatically by design.  Anytime Hot water is wanted, the Open Direct system ensures that this takes priority and Hot water flows from the Calorifier to the tap or shower as long as it is open.  As soon as you close that tap and are no longer needing Hot water, the system reverts to In Floor Heating Mode.

Summer vs Winter:

The difference between Summer and Winter is that in Summer/hot weather when the In Floor Heating is turned off, the IFH Circulation pumps never turn on so no water is flowing through the floor UNTIL a Hot Water tap is opened.  Said another way, the ONLY time water is flowing through the floor PEX is when the system is in DHW Mode because a Hot water tap has been turned on.  The rest of the time, there is NO water flowing through the floor tubes. 

This turns out to be part of the “brilliance” of this type of system in my opinion because the design ensures that the In Floor Heating automatically adapts to whatever the weather is.  HOT water ONLY flows through the floors when it is needed and the circulation pumps turn on in colder weather.  NO hot water flows through the floors in warmer weather because the circulation pumps never turn on.

This sets up the ideal system as it ensures that the water in the PEX tubing is always being refreshed and is never standing still for any length of time.

Better yet, in hot weather, when you are using DHW and there is water flowing through the floor tubes, it is absorbing some of the heat in the room or from sun shining on the floors and so that by the time the water gets to the Calorifier, it is now a bit warmer so you save energy in the Calorifier because the replacement water has already been warmed up and does not take as much energy to heat up to whatever temperature you have sent the Calorifier to maintain.

Once this all makes sense I think you too will see just how “brilliantly simple” this Open Direct system is.  It is completely automatic, no valves or switches to change, no need to drain the system or do anything else other than keep using everything on the boat/house as you always have.

Trust me, it does take a while to figure this type of system out.  It is one of those things where it is very simple but ONLY after you understand it!  To begin with, it can be VERY confusing!  My suggestion, and what I used to do a lot of, is to draw out a schematic for yourself and trace the flow of water in the different scenarios from summer to winter and from In Floor Heat Mode to DHW mode and I think you will quickly see how it works. 

Hope this helps and if it still doesn’t make sense just send me additional questions in the “Join the Discussion” box below to let me know what’s confusing or not making sense and I will do my best to answer them all as quickly as possible or in next week’s post.

Thanks for your patience with this not always so clear ex teacher!