In floor heat system - Passive heat exchange problem 1

[CheckMate]

I am working on a house that appears to be experiencing a passive heat exchange problem. The home is new and this is the first winter use of the in floor heat system. The house is built with plastic tubing run between the floor joists and the basement ceiling deck. Hot water is circulated through the tubes to create a warm floor and to heat the upper story.

The problem is that when they take a shower or want a drink of water there is no cold water in the domestic cold water supply. They need to run the water for a long time to void the hot water (approx. 104F) from the line before the cold water is present. This is a great waste of energy, they are heating water passively that they don’t want and then having to waste water to get the water they need. (The funny side is the kids don’t know if they are turning on hot or cold water, and the toilets never sweat. May be funny but frustrating.)

A secondary problem is the shower p-traps dry out in just a few days and there is the escape of sewer gas.

Is there any design and installation guidelines that should have been followed to prevent these problems. We are looking at going back on the builder and installer to have them remove the ceiling deck and insulate all domestic and sewer lines.

Any thoughts and advice is greatly appreciated.

 

[Darken99]

If it isn't a heat exchange problem, it could also be caused by hot water flowing back up through the cold water inlet on the hot water heater.

Give this a read.

http://ths.gardenweb.com/forums/load/plumbing/msg1101165611579.html?11

 

[Darken99]

By the way, is the water heated in a boiler or hot water heater?

 

[StoneCold]

On all the systems I have looked at on the web the heating tubes are laid on the floor of the room you want to heat and then covered with a light weight concrete or another material to make a smooth surface. If the tubes are ran under the OSB board and between the joist it must take a lot of heat to warm the rooms up because of the insulating factor of the OSB boards. It is no wonder that you are having secondary problems. When I looked at the web again today

http://www.wattsradiant.com

had a system that was under the floor boards like yours, they might be able to help you.

Goodluck
StoneCold

 

[TBP]

I very much doubt that this is an "insulation" problem. I'm much more inclined to side with Darken99's second thought - you've got heating loop water backing into the domestic water supply. Is there an expansion tank and backflow preventor on this heating system? A properly selected relief valve?

This isn't one of those nasty systems that incorporates the heating loop with the domestic hot water supply making them one and the same, is it?

There is also the chance that it's something as simple as a backflow preventer installed at the domestic water supply to the home (now required in most jurisdictions), and no expansion tank at the domestic water heater. This would suggest that the problem may nothing to do with the building heating system.

 

[davefitz]

Its been a while since I read up on the radiant floor heating, but as I recall:

a) some localities will not approve using the same hot water heater for heating and also for potable water supply. The main issue seems to be the bacteria Legionella- it likes to grow in stagnant water that also has oxygen in it.The oxygen somehow permeates into the PEX tubing, even after addition of oxygen sealing coating of the tubes. When you take a shower, you can then breathe in a blast of Legionella, and get mighty sick

b) the radiant heat system usually has a recirc pump, and again the plumbing code will require such a system to have a reverse backflow preventer- maybe they forgot to add this?

 

[RossABQ]

I guess my first question is, why are they "wasting" 104 F water until it is cold, then presumably adding in hot water to bring it right back up to near the same temperature? if they are taking a shower why aren't they just using it? I wish my water was 104 instantly! I can see the problem if they want a drink of cold water.

Also, are the domestic water lines run between the joists along with the heating water loops, and insulation covering the whole between-joist space?

 

[CheckMate]

We see it as a waste. Whenever they want cold water in the house, they have to void the hot out first. Imagine the scenarios: getting a drink, brushing the kids teeth, flushing the toilet, watering the plants, doing laundry with no cold water, ect. If they want hot water, then they turn on a hot water tap. This is built into a $1.4 million new home, and they think it should work properly.

All piping is within the same joist space.

The question is this: "Is there a design / installation guidline / specification that should have been followed by the installers?"

 

[Darken99]

Checkmate,

I have never heard of anyone using a design like this to heat their floors between levels. Like Stonecold said, "If the tubes are ran under the OSB board and between the joist it must take a lot of heat to warm the rooms up because of the insulating factor of the OSB boards."

The idea is to heat through the least insulated surface. That is why electric convection under the carpet or flooring surface is the way to go.

http://www.nuheat.com/products/

I would confirm that it is a heat exchange problem before going any further. They should be able to touch the cold water inlet tube from the hot water heater. If it is hot, there is hot water feeding back through the cold water system.

Regards

 

[IRstuff]

There should be no direct thermal connection between the cold and hot water, except, if the hot water is backing up into the cold supply OR they're using the cold water to regulate the passive heating, i.e., they've run a similar set of piping in the floor directly connected to the cold supply to throttle down the 104º water used for heating.

So, what's the actual temperature of the cold water?

Can you find out if there's a hot and cold connection to the floor heater?

TTFN

 

[davefitz]

well, I'll be danged- if the cold water piping is routed within the same joist space as the heating pipe, then that cold water pipe will be heated up to the heated water temp during periods of zero cold water demand. Thismight be the reason it takes so long to get cold water.

$1.4 million USD- that is a 500 ft 2 condo in san diego.

 

[dcasto]

My house has a heated floor. In the winter, the water out of the cold side takes about 30 seconds to cool down. In the summer, the hot water takes about the same time to get hot. In the summer, the cold water is cool and in the winter the hot water is instantly hot.

All the water lines (3/4" plastic) are bundled together and the 12" diameter bundle runs from one end to the other. Just sitting there, exchanginging heat over to 50' run.

 

[moltenmetal]

What the OP is referring to is a "staple up" radiant floor installation. The PEX tubing is stapled either to the underside of the subfloor or to the sides of the joists, two runs per joist bay. Good installations use formed aluminum plates to conduct the heat away from the tubing and into a larger cross-sectional area of the subfloor. The joist bay is then insulated from underneath, preferably with a radiant barrier.

Normally any cold water lines in the joist space are run UNDER the insulation. Then you don't have to wait as long for cold water, nor do you waste as much energy flushing your toilets with hot water etc.

Other installation methods put the tubing in closer thermal contact with the flooring, by embeddeding the tubing in a lightweight concrete slab or running it in channels cut or formed into a layer of subflooring. You can buy subflooring panels with the grooves pre-formed and the whole top surface coated with aluminum foil. These systems require lower water circulation temperatures to give a warm floor, and give more uniform heating than a staple-up installation. And they cost MUCH more to install. Of course any of these systems work more efficiently with a conductive finished floor surface such as ceramic tile etc. than with hardwood or carpet...

I wouldn't worry about the energy efficiency loss of running the cold water for a bit, though you could fix that by insulating the cold water run. Chances are, they ran the cold water in copper tubing rather than with PEX, making the situation that much worse. You could of course simply put some cold water in the fridge for drinking.

Even when floor warming is done via a staple-up installation, it's still at least theoretically a more efficient way to heat a home than via heating forced air. The warm floor warms all objects in the home, including its occupants, raising their surface temperature and making them feel more comfortable at lower air temperatures. This permits the occupant to set the thermostat lower at similar comfort levels- if they choose to. And the still air is good for people with allergies- all that bulk air movement required for forced air heating re-suspends dust, pollen etc.

 

[a31ford]

Dear checkmate:

I see not all people on this list actually read the original post.... (we'll leave it to them, to re-read it)

Anyhow, YES, there is a set of guidelines for "Joist space" radiant floor heating... and "Bonus" they are on the web... (for free yet)

Here: (You must register, BUT it's free)

http://www.ipexinc.com/Content/Comm...nical_Center/3_1_Technical_Library/index.asp?

WATCH For word wrap on the above, the whole line ends in the portion "index.asp?"

Go to the following "Warmrite floor radiant heating" section
click on it, THEN, click on "Manual of modern hydronics"

Four sections, Gives ALL the details of hows and do/do-nots of correctly installing radiant infloor hydronics (as well as between joist systems, as well as outdoor snowmelt, etc.)

Enjoy !

Regards, "the crazy farmer"
Greg Manning

 

[CheckMate]

Dear a31ford

Thanks for the help. I called Ipex Inc. and talked with a technician there. He said they do not address the problem of domestic lines in the cavity space of the heated area. He said this should be just common sense that any plumber or installer should recognize. But the bottom line is, the heated space will passively heat the cold water supply and it is a major waste and effects the efficiency of the heating unit.

The link was very informative. They had great details on installation. I would recommend it to others.