That is my question!

I finished installing radiant heat in my attic. There is a circulation pump between the radiant floor in the attic and the domestic hot water heater. When I turn on the heat with the thermostat the pump kicks on and the room gets warm. The thermostat and the pump will then turn off.....then the room continues to get warmer and warmer.

It is not just residual heat in the tubing since it goes up from 62 to 70 degrees. I also can manually shut off the valve going to the floor and the room doesn't get any hotter.

I think the hot water in the water heater is rising up to the attic and then the cold water is coming down causing circulation without the pump.

Is there a way to stop this? I can provide any additional info you need.

Thanks so much!

Andreas

You need an electric valve that shuts when the pump goes off.

Not a very good idea to use potable water for heating because you'll have a dead leg growing bacteria all summer. Then it dumps the bugs in your water tank when the heat first kicks on in the fall.

I would use a check valve.

DIY design; always the first mistake.

My open system has a cold water inlet so will have fresh water to the floor every time we shower.

Also, in the summer, all (cold) water will go through through the floor first.

I was thinking about an electric valve, but thought something better was out there.

I have a 1/2" check valve right now, but is not doing the trick. I have it positioned horizontally, so don't know if it would change anything going vertically. The weight of the flap has to prevent the rising hot water.

I was told about flow control valves, but am having trouble locating them.

Finally found these at my local professional plumbing supply: http://www.bellgossett.com/literature/files/607.pdf

These are designed especially for this problem as opposed to a check valve.

Posted By BadgerBoilerMN on 22 Feb 2010 08:25 PM
I would use a check valve.

DIY design; always the first mistake.

And open systems seem to be a close second in the radiant biz...

The convection can conceivably run in either direction, depending on the layout.  If a check valve isn't cutting the mustard, a zone valve will.

But as long as you're hacking on the system, a heat exchanger at the HW heater, converting it to an isolated system could potentially fix a world of ills.

To tell you the truth, I'm not sold on an isolated system. There are advantages to an open system. The design is not DIY. I used these two schematics: http://www.radiantec.com/systems-sources/open-best.php and http://www.radiantec.com/systems-sources/open-summer-cooling-mode.php

there are no significant advantages to an open system other than first cost. What incredibly minor advantages it has are spun into a massive marketing effort by those who are preying on the ignorance of others to sound like "advanced system design" when in fact they are simply corner cutting hack tactics.

-with a variable speed pump on the potable leg, energy usage increase is very small. as in, $5 to $10 a year in most cases. You need a VSI controller for this, which adds a bit more cost, but then you have reset operation in the system which is vastly superior for comfort and noise control anyway.

-Efficiency loss is very small or completely insignificant in all cases except where your design water temperature is very close to your stored temperature. which can be avoided many, many ways. if the radiation of the heat exchanger itself is an issue, insulate it.

-the "limited free cooling" is a ridiculously "limited" truth, and it presents a significant condensation risk.

-bacterial risk is amplified, though to different degrees in different systems.

-leak damage risks are much higher in open systems than they have to be in closed systems.

-potential for equipment failure is much higher in open systems than in closed systems, from calcification, dezincification, to general gunk, to electrolysis... all of the mass failures in radiant systems in recent years that I'm aware of have been freshwater systems.

-a boilerplate schematic is not a design.

the cost difference between freshwater and sufficiently closed is typically something like $350 to $750 and you could add about $250 or so of that if you wanted reset operation and added the variable speed controller, and I think it would have positive payback characteristics on pump energy and results in a better system to do that (and we always do in this configuration). This is a one time insurance policy that protects you, your house, and your system forever with no other significant downside. on a very small system, that's a big percentage of the initial cost, but in that case, you're at the bottom end, roughly. for a system of any size, that's still real money, but it's the difference between a hack job and doing it right and as such it's a pretty small price to pay.

I have nothing good to say about freshwater systems or the people who sell them. Nothing but marketing tactics support such designs.

Thanks for your comments.

Yes, the cooling is limited, but my attic is well insulated with spray foam. It may make the difference between needing a window AC unit, which would be a significant benefit in my case. It also warms the water before it goes to the water heater for additional small benefit.

Seems like leak damage is present in water radiant heat no matter whether you go open or closed. You could make an argument for electric radiant or forced air in that way. In fact, having a bathroom is a leak risk.

Do you recommend against circulating instant heat? It seems like that is similar to an open radiant heat system. You need a SS pump, the oxidation issues/equipment failures, and Legionella increased risk...but maybe there are people that are adamantly against them?

I don't think that radiantec is using marketing tactics since they don't actually sell installation -- only parts.

In any case, it seems like a different way of doing it as opposed to a "hack" method. $750 is significant to me, although it wouldn't break me. I bet my system is $9k less than what I could get installed to do the same thing.

It should be noted that no plumbing or heating (mechanical) code in North America accepts the "open" systems that Rob describes. But nothing sells like cheap. Science, experience, wisdom all taken a back seat to cheap.

the limited cooling here will never replace any active cooling unit, ever. "limited" means "practically negligible". I believe it also warms the water going to your tap, or the benefit is even MORE limited if it's only the hot water preheat. and you're ignoring the condensation risk, which is much more significant if you are not otherwise dehumidifying the home through an active cooling system.

Leak damage is present, but in a closed system, you can close the fill valve, if you used one, and then only the water content of the pipes is a risk, which is a fairly small damage risk.. In an open system, or a closed system with an open fill valve, you have an endless stream of replacement water. this can happen in plumbing as well, of course, but you might guess that punctures and leaks are a tad more common in radiant systems than in plumbing systems since there is generally at least 10x the pipe involved and it's often under nailed finish floor surfaces.

recirc is not similar to an open radiant heat system. the amount of pipe involved is very small in a recirc system. recirc is similar to a short leg to an air handler, a practice which is widely regarded as safe for the same reason... it's just not much of a home for any bad stuff. though I will note that european domestic systems go into a "sanitary mode" at least once a week that elevates the tank temp high enough to kill bad boys. that seems to be a better practice then we have here in the US.

I'm not quite sure how "not selling installation" means that the open system sellers are not using "marketing". their sites are covered in marketing talking about how everyone is ripping you off, how open systems are cutting edge technology, and a variety of half truths and bad information that support their "conclusions". apparently you have a definition of "marketing" which requires someone to turn a wrench or be an installer?

Obviously you can save a lot money doing lots of labor yourself. I have nothing against DIY as long as you're not installing combustion appliances and in fact work with them all the time. But there are corners that should not be cut, and encouraging people who don't know any better to cut them to APPEAR cheaper is a practice I take a very dim view of.

Posted By BadgerBoilerMN on 23 Feb 2010 08:42 PM
It should be noted that no plumbing or heating (mechanical) code in North America accepts the "open" systems that Rob describes. But nothing sells like cheap. Science, experience, wisdom all taken a back seat to cheap.

IIRC open systems are specifically allowed in MA, provided that the circulators run a minimum of 5 minutes out of every hour, 365 days/year.

I'd never do it though- the advantages (when they exist at all) are miniscule, and the risk potential varies with many factors, not all of which are in your direct control, eg:  the verifiable quality of the incoming water.  Some water can stagnate with very low biohazard potential, some doesn't.  Should the system ever become infected with pathogens, disinfecting it may be difficult or impossible.

I stand corrected never having looked to MA for design standards.


Thank you, I doubt the open system pushers even knew that one.

Posted By BadgerBoilerMN on 24 Feb 2010 02:50 PM
I stand corrected never having looked to MA for design standards.


Thank you, I doubt the open system pushers even knew that one.

They probably did know, since it's footnoted in some of the (formerly available online) kludgy schematics published by Takagi in their "representative systems".  A number of web-store open system pushers are all over Takagi, since Takagi doesn't void the warranty when their goods are used for space-heating/combi systems.  I've noticed that in their more recent manuals they now have notes that the circulator pumps to radiation must run 60 seconds out of every 6 hours, but no mention of MA related to that requirement (possibly just a CYA on their part?)

MA has a number of peculiarities to their code relative to some other states, eg.: Check-valves on potable systems must have a 1/8" hole (presumably to allow for expansion issue).  But they don't allow DIY installation of gas burning appliances of any type (including hot water heaters/combi's), only licensed plumbers with gas fitter certification, whereas many states will allow it, with a local inspector's signature, etc.

But allowing open combi systems isn't necessarily a recommendation or an endorsement of the approach.

Hmmm... in diggin' around I can't seem to lay my hands on the spec for legal open systems in MA- I may be mis-remembering...

Don't count on the details of my prior postings on the subject for absolute accuracy.