I am back with more questions!

We are getting closer to our final design - but still are completely open to whatever we need.

Talked with the Radiant Heat Subcontractor that our GC uses yesterday - he didn't like the idea of a condensing tank heater, said he really didn't like the Polaris, thought they were poor quality and had service problems. He was more interested in using something like Navien's Combi Water Heater with the separate circuits for DHW and RH...I asked him to look into other Condensing Tank heater options as that was were I was hoping to go. I will see what he comes up with there.

We are trying to get the whole heat package down to under $20K - right now if we do radiant sandwich type system upstairs we are at about $26K (No Warmboard at this time) - we are looking at Quik Track Ecowarm etc...

I talked to him about doing the upstairs with Runtal Radiant Baseboards instead of in-floor hydronic as that would save us several thousand - I am thinking that might be one good alternative - the ductless mini-split being the other. We have three areas where the baseboard radiators could easily go under a window that will never have items or furniture placed in front of...plus our home design will be modern so their units could blend into our design pretty well.

My questions for the experts here are as follows:

Best condensing tank model(s)?
Are the Navien Combi units any good? Better than a condensing tank unit?
Are Runtal Radiant Baseboards good as an inexpensive alternative? We could upgrade at some later date to in floor if we wanted or disliked the baseboards.

Thanks again everyone here, and sorry if my questions keep coming, but I want to make educated choices!!!

The heat source is determined by the available fuel, the total heat load and the dynamic loads of the heating system.

On small loads, especially under 50mbtuh, I use various condensing tank water heaters, as they will allow small zones to call more often without short cycling the burner, which can affect both combustion and operating efficiency. Small loads also imply small spaces so integrating domestic hot water and space heating - without using potable water for both - saves physical space and time of installation.

Panel radiators (Runtal is one of the most expensive) make great sense in many upper floor applications, as they can be individually controlled, oversized for very low design water temperatures and are second only to radiant floor heating for comfort (forced air being a very distant 4th).

Polaris water heaters have been made from scratch in a US plant in Johnson City, TN (since 1987 if memory serves). Navien by contrast, besides be misapplied in this instance is new by any standard of time. I do not use tankless water heaters for radiant heating systems as boilers are made for this duty.

A.O. Smith Vertex, State Premier and yes the American Polaris all are rated "suitable for domestic hot water and space heating". I would consider a design professional to properly size and specify the equipment for comfort and efficiency.

Part of the problem locally is that there aren't a lot of new homes being built (we are built out - plus the economy is still hurting) so there are very few choices/competition/knowledge locally. Now the current subcontractor surprised me with his suggestion of a tankless (I don't remember the exact model actually) but he liked it - I don't.

So my task is to find out if there are true reliability problems with Polaris or if there is a better choice in the condensing tank realm.

Navien (Kyung Dong Boiler, Korea, renamed KD Navien about a decade ago) has been making boilers since the late 1970s. Their first wall-hung stainless-steel gas-fired combi-tankless units were built in the the early 1990s, but marketed only in Asia. They got into condensing boilers fairly late in the game about a decade ago, and condensing tankless HW units shortly thereafter (allegedly with some engineering talent raided from Takagi, if scuttlebutt has it right.)

KD Navien owns the lions share of the Korean hydronic boiler market with their wall-hung gas boilers. This is a company that knows the difference between a hot water heater and a boiler. SFAIK their wall hung boilers (other than the condensing combis) are not sold in the US, but they do have a toe-hold in Europe. Their condensing tankless combis are a relatively new design with very little track record. Service on their N.American tankless HW units seems spotty, and the vetting of installers not well controlled, if internet forum postings are to be believed. But if competently installed by an installer familiar with them I'd expect reasonable longevity & performance.

Whether it's the right unit for a micro-zoned low-load low mass radiant system is another matter. Any low-mass boiler can short-cycle itself into an early grave when combined with low-mass radiation broken up in to zones that deliver but a small fraction of the boiler's output. This is a system design issue. By contrast tank type HW heater base systems are high mass and inherently self-buffering- they literally CAN'T short-cycle, making them easy to design systems of reasonable efficiency around.

This may be too expensive for your budget, but the Versa Hydro or Versa Flame are pre-packaged self-buffering gas/LP fired combis that doesn't take a lot of system design skills to make work: http://www.htproducts.com/versa-hydro.html http://www.htproducts.com/literature/HTP-Versa-Flame.pdf (The smallest burner & tank Hydro or Flame would be more than enough for endless hot water and heat in your situation.) These units come with outdoor reset control, which might allow you to squeak another percent or two of efficiency out of the system over a Polaris or Vertex if your system needed water any hotter than DHW temps on design day, but that feature is probably not worth paying a lot extra for in Santa Cruz. (For fin-tube emitter heating systems in cold climates it is though.)

I'm impressed Dana, you are a quick study and a wealth of information.

"Talked with the Radiant Heat Subcontractor that our GC uses yesterday - he didn't like the idea of a condensing tank heater, said he really didn't like the Polaris, thought they were poor quality and had service problems."

When people - be they professionals or amateurs - deride equipment, I have to ask: How many have you installed?
The other thing I like to ask is, why the GC uses the heating contractor he recommends?

The Polaris, or any condensing water heater, can be fit with heat exchanger and outdoor reset, which in practice is often more about comfort than efficiency, regardless of climate. Any homeowner should check for local support, as Dana correctly points out. Dana also make a good point about condensing boilers on low-mass radiation such as, the Runtal radiators you suggest and I would add that panel radiators with flow restricting thermostatic radiator valves (TRV) can make things worse.

In the end, the heating equipment you choose is only as good as the man that installs and maintains it. A savvy designer takes location into account both in the design and specification researching what is available and the quality of factory support in your particular area. Here in Minneapolis our cold weather and population afford us many choices, but in warmer and less populated areas I often steer radiant heating clients away from some of my favorite condensing boilers and water heaters.

We can all agree that the high mass of a storage type condensing combi water heater can be the perfect match for European steel panel radiators with TRV’s and perfect control in every room. That is, if all is designed and installed correctly.

One of the large heating contractors in our region (Halco) also recommended the Navien combi- though I needed the propane condensing model and that was not available yet. I researched the Navien combi gas model online and found way more complaints than I did complements about it.

I also researched the AO Smith Vertex 100 condensing tank hot water heater, and that came up with a much more positive overall result as far as comments went. I do realize that it may have to be replaced sooner that one of the more expensive models, but was willing to factor that in, considering the $2000 price being considerably less than any other options I looked at. It was extremely easy to install and hook up to both the DHW system and the radiant floor heat exchanger, given the 2 sets of hookups designed specifically for this purpose, and being direct vented using PVC, also an easy install. So far it has been working perfectly to heat the house efficiently, (ave night temp 29, night time low of 19 high of 54 - average cycles 10.5 per day with a propane use per cycle of .157gal, keeping the house air temps at 60 degrees which is as warm as I like it) and do the occasional load of laundry, though I will not get its full measure until we are living in the house and go through a full heating season.
-Rosalinda

how's the sound levels with the vertex rosalinda? can you hear it running? outside the mech room? upstairs? next door?

Rob,
I don't notice the sound when I am upstairs in the main living area. It is not that loud even in the utility room, more of a whirring sound as the vent motor runs when it is firing. There is no sheetrock on the ceiling of the utility room so no buffer between the floors. If I am behind the house on the vent side there is a noticeable roaring sound when it runs, but not disturbingly loud. Usually I think, what the heck is that noise? - then ahhhh the Vertex. It is definitely quieter than the old propane forced air furnace in the old house. The old house is about 50 or so feet back from the vent side of the new one, and I can't hear it from there.

-Rosalinda

There are quieter options.

I have been an authorized repair company for Polaris for over 20 years. They had some problems in their early designs, but for the most part now they are pretty reliable. Navien has had some real problems with their heat exchangers. I will not specify Navien or install them.Noritz has a nice condensing boiler which you may want to take a peek at. Runtal products are very well made, but they would need to be installed through a heat exchanger. Water treatment is a must with Runtals.

Good points wizard. Open systems and panel radiators don't mix...for long, although no water treatment is needed in most properly designed and installed residential hydronic systems. My own Runtal towel warmer has been in service since 1992 without the benefit of treatment.

Condensing boilers (nearly always my favorite heat source) will not do well if oversized. Since most are oversized, especially if the owner or contractor uses a free online heat load program, the boiler will tend to bump off the bottom negatively affecting comfort, economy and liability.

The high mass of tank water heaters is a perfect match for micro-zones on systems large and small. If you have a sun porch, three season converted to four or room with more than 50% windows you have a zone that will call when all others are satisfied, this is a micro-zone and must pull energy from a stored reservoir or turn the boiler on and off. If you want perfection a condensing high mass tank water heater offers sealed combustion, PVC direct vent, 96% thermal efficiency and quiet operation depending on the brand, the perfection comes with the addition of outdoor reset and/or modulation. Outdoor reset sends heated water to the radiators or radiant floors matched to the load of the house and that keeps them on more of the time. The result is perfect comfort and economy. Sizing the radiation, be it panel radiator or radiant panels, to one design temperature makes for a much simpler and reliable system.

Open systems and panel radiators have a similar share of the market in the UK as forced air does in the US.

They do work.

Open systems?

Just to be clear, the advantages of buffer tanks also apply to geothermal - better efficiency due to lower temps (with outdoor reset), no short cycling (even with zones), higher peak output and the potential to shift loads to off-peak electrical rates. Maybe even less noise from radiators and pipes.

"Open" systems (those using potable water for space heating) are NOT compatible with steel panel radiators and are not common practice in Europe or anywhere else. Where they make sense is in a Combi system where one appliance - in this case a tank type condensing water heater - provides heat for space and domestic hot water but the space heating is mechanically isolated from potable water - normally by a SS plate heat exchanger or an assembly utilizing one.

I expect our design will use a heat exchanger - that seems the safest since we won't need heat the majority of the year, and I don't want a complicated flushing system or anything of that nature.

Based on several of the comments above I want to make sure I understand things correctly. Assuming a heat exchanger is used, and a condensing tank heater (my preference), can we mix radiant in floor and the runtal baseboards upstairs - all zoned separately - and be OK?

I understand that the Runtal is designed for 180 degree water - but would be ok at 120 degrees - we will need to spec larger Runtal radiators to compensate for the lower temp running through them I expect.

We have 2 north facing walls and 1 west facing, all with windows above, that easily can take a 6" or 9" high Runtal in 8ft-9ft lengths - I have a few other locations that might work for the additional heat I may need...

Our calculated hourly heat loss for the entire upstairs is 18,500 - on a liberal design day.

Posted By acwizard on 18 Apr 2011 12:43 AM
Noritz has a nice condensing boiler which you may want to take a peek at.

I think I may be mistaken in him recommending Navien - he might have said Noritz...

To many models/mfg's running around in my head.  Probably the Nortiz Tankless Combi unit he liked I believe...still an open system I think

I was talking about an open heating system. You have to treat the water in a radiator system, certainly not drinkable. Probably kill you.

Como said; "I was talking about an open heating system. You have to treat the water in a radiator system, certainly not drinkable. Probably kill you."

Open heating systems are not approved anywhere. They use potable water for space heating and again for consumption. The only exception is close-coupled fan coils running directly off a water heater at design temperatures.

The water in residential hydronic heating systems “radiator system” employing panel radiators, radiant panels or fin-tube, with rare exception, is NOT treated. It is doubtful that bonier water would kill you since it was potable water going in, if not out. Hydronic heat transfer fluid (almost always potable water to start) should never be replace or refreshed as it is conditioned by having the oxygen driven out of it making it suitable for use with ferrous metal components like pumps, expansion tanks and steel panel radiators.

I think you are just messing with me or perhaps we have a new "expert"...

I think Como is talking about an unpressurized heating system. Any system without an oxygen barrier is open. not all are combined potable water systems. Most current outdoor wood boiler systems are open but not potable.