What do you find works well with the Warmboard system?  We have a DIY client that is trying to make a 3400 sf house with Warmboard work with a Takagi IG water heater.  This doesn't make sense to me, since Warmboard is a low temperature system.  We had expected a Munchkin with a Storage tank for the hydronic loop.  Lately, I've been thinking that the Phoenix Hi-efficiency Storage Tank Type Water Heater would be a better choice.

During heating periods, I would expect the water loop to be constantly charged with warm water.  Ideally, the entering water temp and the returning temp would be close when the whole system is up to temperature.  I suspect that when the Takagi gets a heating call, it pumps out 135 degree water and as soon as the thermostat registers 70 degrees (or whatever), it shuts off allowing the temperature in the whole loop to drop until the air temperature again drops below 70.   This is the way a forced air system works, but doesn't seem to make sense for a radiant floor.

Should we recommend sending the Takagi to Craig's List and installing the Phoenix?

Consider using a storage tank with the Takagi. Run the water from the tank through the tubing, and heat the water in the tank with the Takagi. The storage tank will buffer the heat output from the Takagi. With mixing valves and manifolds you can build a dream system for maintaining temps throughout the house and avoid heat and cold surges.

I am building a 2400 SF house in Portland, OR, and am planning to use Warmboard. With all options for the domestic and hydronic water heating still open, what would make the most sense to use? (efficiency and affordability) Also, we would like to keep the option to add solar water pre-heating (for the domestic water only) a few years later. Thank you for any suggestions!

I am not sure about the Warmboard but we use a Takagai to heat the water for our infloor radiant.

We have a remote temp. control on the system. We have the water set to 115. We can see the temp of the incoming and of course the outgoing as well. I think we can set it as low as 95.

The Takagai only heats to the temp we need, no more no less. We find that it works very well.

actually, that's not true. by definition you are heating above the temp you need, since the temp you need when it is very cold is not the same as the temp you need when it's mild out ;)

"actually, that's not true. by definition you are heating above the temp you need, since the temp you need when it is very cold is not the same as the temp you need when it's mild out ;)"

Was this in response to my post?

yes, in relation to water temp... just being a nitpicky heating dork. I'm not a fan of on demand water heaters for heating most radiant systems, especially low mass systems, but that's a separate issue from the fixed-temp issue.

Okay let me re-state. We heat the water to the temp it needs to be to raise the temp in our home as fast as we want! It gets colder and I can raise it up.

I see that most systems heat the water up and then have to use a mixing valve to cool it down.

We have a high mass system,( 3" slab) and a small house. My Takagai usually runs at its lowest output and only needs to run a couple of times a day.
If I were running a system that was under constant demand, I would look at a boiler look at other systems.

I know what you meant, I was just nit picking because it's what I do. the best control is one that varies the water temperature with your load. the "heating up and cooling down" issue isn't much of an issue really, but it is better when the heat source can be run at the temp you need. mod/con boilers w/outdoor sensors are a great choice; for a small, one zone slab system, perhaps not warranted. In your case, technically the takagi is running hotter than needed most of the time. with a low load slab system, you might even find 90 degree or 100 degree water adequate most of the winter.

In your case, a takagi is ok though, you've got probably the best type of setup for justifying its use (minimal cycling, minimal load). In more typical cases (lower mass systems, more zones, etc) I would spec a tank water heater before a takagi to deal with more prevalent cycling issues.

Thanks for all the replies. To put it into my own words, because we have a low mass system (no slab), there will be more frequent demand for hot water (makes sense), and therefore it may be more economical to serve that frequent need with a boiler/tank heater rather than an on-demand heater. I can see how it would be desirable to have a tank as pre-heater before a tankless device but am not sure that I can afford to buy two heaters. How would that cost be justifiable? Are there any good tank/boiler heaters for radiant heating systems? Let me know if I have anything wrong.

Rob, feel free to explain a bit about why you do not prefer on-demand for radiant. Would love to hear all sides!