Hi everyone, just to preface I had my radiant heating system designed my the Radiant Design Institute (Fred Seton). Fred told me that the Phoenix PH100-55 would be able to supply both the radiant and domestic. From what I have been reading I want this system to run in closed system. Which I believe means that the domestic hot water supply is separate from the radiant.

What I can't figure out is how it possible for that function correctly? I look at the water heater and it has a inlet and outlet. Best guess is the water stays separate because of the heat exchanger?

Could someone explain the concept to me?

Yes I will
The concept is that the Seton designs are over priced, over pumped, over standard loop lengths (500' 1/2")average, Open loop, Won't work efficiently.
Consider yourself lucky if you have not installed yet
Or is it over to late. ;-)
Dan

Thanks Dan, I know you are not fond of Fred's work.

System is not yet installed but I in the process of buying the Phoenix. But that wasn't really why I posted. I am trying to understand how the Phoenix can supply domestic water while providing the radiant in close loop fashion.

It does not, Google the product schematic, it is a very good water heater. It does not include a heat exchanger, not the model you identify.
Seton is selling you an open loop design. If it fails to make heat loss who will answer the phone in his shop?
Placing a Taco 0014 pump against a pile of actuators with a by pass valve is a bad design.
running 1/2 pex 500 feet on a staple up is a bad design.
My opinion.for what it is worth.
Dan

Hi Dan,

His plans although not what I would consider super detailed do have an option for closed system. This option calls for a AIC Plate Heat Exchanger. I have the manual from the manufacturer just not understanding the heat exchanger part.

You know even after a few years of reading on this topic I can't seem to find people online saying there system is failing and/or negative comments. Could you maybe throw me a bone here and point me into the right direction or point out a few threads in which people say the guys doesn't know what he is doing?

PS just came across this which answers my original question.

"An Indirect System is one in which the domestic water heater supplies heat to the radiant heating system “indirectly” by means of a heat exchanger. The heat exchanger separates the potable domestic hot waterfrom the heating system fluid."

Would still love to hear more about Fred's designs Dan. We have been on a low budget for over 3 years and only now coming to the point we can afford to start buying what he recommended.

Open combi heating systems are not accepted by any model building code in N.America. The few that advocate open heating systems are simply trying to play on the universal human instinct to find a bargain or delusion that we have when we really have only be deceived.

This is a specialized field in which few professionals actually no what they are doing. How can one find an online vendor that sells radiant floor heating components that can be trusted? Well this site is one way, but you have to pay attention.

Here in Minneapolis, where open heating systems are illegal, we are licensed to by the city to install plumbing and heating. We specialize in radiant floor heating and often use high efficiency water heaters for combi duty, providing heat and domestic hot water with one gas-fired appliance. As homes get smaller and more energy efficient it just makes good sense to combine duties, especially as the condensing appliances save fuel and the environment.

If you want to use HTP equipment you will want to consider their VersaHydro, which combines a plate heat exchanger with a condensing water heater and all necessary controls for a perfect radiant floor heating combi DHW heating system. We will be installing on next week as a matter of fact to replace a poorly designed systems just 7 years old. It is sad to see such waste for lack of proper planning.

If you have a standard water heater then a sub-system is the answer. Using a plate heat exchanger and other components to isolate potable from space heating water for longer, safer system life. Take Dan's advice. DIY radiant floor design is usually the first mistake.

Hello Cloves,
Let me clarify my thoughts. We design ans supply DYI systems all the time. Have been doing so for 14 years now, however we stick to RPA guide lines on loop length, we advocate delta T pumps, zones that are reasonable size, heat transfer plates as needed, insulation under slab and more. We try to design systems that can be successfully installed and will work efficiently. We do not design open systems, rarely will design around a water heater, we do like the x block in some smaller applications primarily retro fit. If you want an open system, go for it. There are to many reasonably priced combination condensing boilers that will provide domestic water on demand and low temp heating isolated to make me think a 55 gallon $4,500.00 water heater plus strap on heat exchanger is a good choice. But it all depends on what a person perceives as good. No doubt the Phoenix is a quality appliance. I suspect you will have some of the same technical issues as with a wall mounted condensing boiler.You will need a technician either way to help along the way perhaps.
As to Setons designs, we have corrected quite a few, I have looked a a lot, we use to supply some of his clients but I offered my opinions to often and fell out of favor as a preferred vendor.
We all make our own choices,
Good luck,
Dan

Cloves, Listen to Dan. He will not steer you wrong. Long loop lenghts should be avoided.Phoenix is a great product but is not always the right fit for every application. Seek some professional help,in the long run you will be more satisfied with your heating system.

Thanks everyone for your feedback. I am going to reach out to you guys via PM to get a rough idea of what I am going to be looking at for having the designs redone (I can supply the designs I paid for and perhaps that can be a starting point). As far as materials, I have purchased 6 500' of Pex tubing, hopefully if we can afford to get them redone I can still use those. Going to hold off on the Phoenix.

combustion heat sources should always be purchased locally through a licensed and trained technician who can service the units and ensure they are operating properly and safely from the get go.

I do think condensing water heaters are fine but condensing modulating boilers can be better, if designed properly.

overpumping is a bad idea. open systems are a bad idea. and never run multiple rooms on the same loops!

Rob is right, but.

We are local, licensed and trained and use many condensing water heaters in our work, which is mainly the sales and installation of condensing boilers with radiant floors. The condensing water heater fills a niche where small zones or spaces require high efficiency in both space and output. The storage/tank type condensing water heater is usually (specific to brand) very well insulated and lacking an atmospheric vent will lose a negligible amount of energy in stand-by. Where the storage water heater has no peer is in combi space and DHW service more especially when micro-zones or small areas with large heat loads e.g. sun rooms can't be avoided.

We recently remedied a very cold sun room in a very large home using the existing water heater as a heat source. This problem is so common it is hard to believe people still build them without the benefit of radiant floors.

With the smallest condensing boilers reporting a minimum output of 10Mbuth, a condensing boiler just doesn't fit.

that's a pretty small niche.

You would be surprised :-).