Open VS Closed Radaint Heating System

John Reist

The recomended a Polaris 34 gallon 100,000 BTU water heater.

John Reist

Open VS Closed Radaint Heating System

am looking at a radiant floor system for a log home that I will be building. The company that I received a material quote from was recomending an Open system where a single high efficiency water heater is used to provide domestic hot water and radiant heating. This is opposed to a closed system that would use a dedicated hot water heater for radiant heating. The disadvantage of a closed system was that I would have the cost of purchaceing and operating two water heaters.

The problem that i have is that I have received different view points on these two systems. I asked the dealer about stagnet water in the system, but being that it is open when you turn on the hot water the water flows into the house through the radiant tubing and into the heater refreshing the water. In the summer a valve can be switched so that all the domestic cold water flows through the tubing providing cooling as well as refreshing the pipes.

Could someone give me their experience with an Open System

kpc_20

do a search...

onthe site on open systems...I would not even consider it. The systems/ systems you describe sound like a very cheap low quality set up...kpc

jp_2

more info

what size water heater do they recommend and how efficient?

Rich L.

open systems

Check out the posting: "Legionella & Water Heaters-Seattle Times"

At what point does saving money come before personal satety?

Chap

Free cooling?

Do the math & you'll find there is no real benefit. Then think about condensation in that insulated floor-joist area & read up on mold growth.

If you're on a municipal system, the incoming water will likely be at or higher in temp than the 78F you may be setting the air-sensing stat! No cooling there.

If it's well-water at 55F, you can check with Tim Doran who crunched the numbers for me several years ago. The relatively short time-frame when water is utilized and the minimal rise in temp from entry to use (cold line) grant very little in the way of A/C. You'll spend more in electricity to run the pump (if you buy into the pump & dump to gain "free" A/C) than you would to operate the real A/C.

You should also check up on the pressure-drop per foot on your tubing. Add 1-PSI drop for every 2.31' rise in elevation too! The codes require you have a minimum 8-PSI residual pressure at the fixture when you have the water running. Depending on how this system you're contemplating is piped, you may also be setting up a scenario where the chances of being scalded are greatly increased.

But, last & certainly not least - you are setting up a very suitable envoironment for bacterial amplification. The stagnation portion of bacterial amplification does not solely rule out bacterial amplification - it simply transports the free-roaming bugs onward to colonize the low-temperature water heater, the distribution network of piping and each distal site where you have contact with water. Aerators on faucets and shower heads emit fine mists of water droplets that can be inhaled deeply into the lungs - a perfect breeding ground for bacteria like Legionella. Meanwhile, back on the bacterial amplification farm, the biofilms present in ALL piping are colonized and bacterial growth continues unabated - regardless of flow or stagnation. Plastic piping offers a more hospitible environment than does copper and horizontal piping permits more biofilm build-up than does vertical piping. Toss in multiple loops at a lower flow-per-loop and the layer of junk can build more quickly (no velocity scouring).

John Reist

The system is from Radiantec..com

http://www.radiantec.com/systems-sources/open-system.php

Tom Hopkins

two water heaters

You don't need two water heaters to have a closed system. You can simply use a heat exchanger to separate the floor heating from the domestic water. Whether this will be effective depends on the load and the water heater size.

I don't think using a heat exchanger on a tank style water heater is a bad idea in and of itself. If the size of the heating load is relatively low, say under 40K BTUH at design, this could be a good approach. Adding the heating load to the water heater essentially makes it more efficient by reducing the wasted standby losses. Also, using a tank style water heater gives you a built-in buffer tank, allowing micro-zoning at essentially the cost of thermostats and thermal actuators.

However, I suspect that if you look into it further, you will find that a high-efficiency Polaris water heater is not such a good choice. It's expensive, and the near-universal experience, as far as I can glean from web research, is that when run at condensing temperatures they drip onto their ignitors, thereby causing the failure of the ignitor.

Perhaps the Polaris has been changed since I looked into it. Heat Transfer Products makes some interesting looking water heaters that might be the call, but I can't say; I have no experience with them.

Mike T., Swampeast MO

The simple system you're examining can work reasonably well when installed in a suitable structure. Therein lies both its strength and weakness.

While simple and inexpensive will prove comfortable and reasonably economic only if the structure is designed to work with the heating system.

Log homes are frequently tough candidates for radiant floors heating. Ceiling/roof combinations, difficult-to-estimate insulation and infiltration and larger glass areaas often combine to require supplemental emitters in some climates.

If you really want to use this system, conduct a thorough heat loss calculation, determine heat requirement per sq.ft. of heated floor area in each room/area. The requirement for suitability is on YOUR shoulders alone with this system.