Sorry to keep bugging you guys, but why on earth would I buy a 50 gallon Polaris for $3k+ when I could get a real hi-ef con boiler for the same or less? The Polaris are so much higher in btu, too. I welcome help in understanding your reasoning, notwithstanding the bad reviews I've read about the igniters and other troubles. And the Versa Hydro is like, $5-6k? I've done lots of homework, so this recommendation struck me as odd.

I already have alpha pumps, two zones, and a good copper manifold set up. Seems like all I would need is a nice boiler for years of service and low gas use.

So the goal is to produce hot water for both radiant heating and also domestic hot water in a efficient way.
One good way ,is a boiler with an indirect storage tank. You want a small boiler with a large turndown ratio so it is acting at maximum efficiency most of the time. The problem with this set up is that you need enough storage capacity in the indirect tank so that you don’t run out of hot water if you have multiple draws in a short time. The boiler does not have enough btu output to keep up so that you need the storage. This was not a problem with a large oversized boiler, because it could keep up.
The other good way is with a unit that combines the tank and the boiler. Here you can get away with a larger heating unit because you have lots of mass to heat up (the tank) so it does not short cycle. In low load applications these can be quite efficient.
Cheers,
Eric

Online reviews are nearly 100% DIY and anecdotal.

Choosing between the Polaris and the VersaHydro (both Energy Star qualified, is not for the novice. It is a question for your designer once the Manual J is performed and the DHW loads are determined.

The proper comparison of these loads and your personal goals will best determine the right appliance for the job.

We use properly sized condensing boilers, combi-boiler, boilers with indirects and many, many, condensing water heaters with sub-systems for space heating those small homes are micro-zones within them without short-cycling or suffering cold showers.

We call them heating "systems" and the heat source is but one component thereof.

Could you please provide any documentation regarding the HTP Versa Hydro ( not versa flame) being Energy Star certified. I am not trying to be adversarial. I have just installed this boiler and have been denied rebates from Efficiency Maine on the grounds it is not Energy Star certified. HTP website is a bit misleading. And after speaking with them they determined it's not Energy Star certified but I am not confident in their answer as they initially told me it was certified but then recanted when asked for documentation to provide Efficiency Maine.

Posted By Eric Anderson on 11 Feb 2015 08:08 AM
So the goal is to produce hot water for both radiant heating and also domestic hot water in a efficient way.
One good way ,is a boiler with an indirect storage tank. You want a small boiler with a large turndown ratio so it is acting at maximum efficiency most of the time. The problem with this set up is that you need enough storage capacity in the indirect tank so that you don’t run out of hot water if you have multiple draws in a short time. The boiler does not have enough btu output to keep up so that you need the storage. This was not a problem with a large oversized boiler, because it could keep up.
The other good way is with a unit that combines the tank and the boiler. Here you can get away with a larger heating unit because you have lots of mass to heat up (the tank) so it does not short cycle. In low load applications these can be quite efficient.
Cheers,
Eric

The problem in this case is likely the low peak load and the inability to modulate even at the wintertime average load.  Maybe the Lochinvar WHN055 could be set up to modulate a bit, most others would not. Modulation has limits- if the average wintertime load isn't at least something like 2x the min-fire output of the boiler, the modulation benefits would be mostly theoretical, and hard to measure.  The fact that it's probably a miniscule whole-house design load and it's split into two even MORE miniscule zones makes me believe that the modulation with the heat load is going to be near-zero here no matter what boiler gets hooked up.

That's where the thermal mass of an HTP Versa or Polaris comes into play. The modulation with the heat load is forgone, but since they will run a lot fewer burn cycles compared to an oversized mod-con.  And you get substantially better domestic hot water performance out of them without having to buy ah extra-large indirect heated by the world's smallest mod-con to get the modulation benefit.

The installed cost of a mod-con + indirect + necessary plumbing & controls is not likely to be substantially cheaper than a Versa or Polaris based system either, even if the boiler itself is cheaper.

Getting the ACTUAL fuel use number between two exact METER READING DATES would get a handle on the real heat load of this place, and whether a mod-con would make more sense than a self-buffered high system.  It's not hard math.

I currently use a tankless for hot water, and am very happy with it. One day in the far off future, I would consider adding an indirect to whatever boiler I get now, but that is far off. Actually, I've considered forgoing the indirect anyway exactly because of the btu conflict between heating enough domestic hot water on the one hand, which is huge, and the floor heat output we actually would need which is so much smaller. We have four daughters and one son, and my partner and I are super big daily bathers, not shower/ers, and have a large deep tub, and -- whew -- if it weren't for the Takagi H3 we have, the whole household would have fallen apart by now. The takagi is the only thing I can imagine that would keep up with our laundry and bathing. BTW we siphon off waste to water the garden. We at least try to be green. :-)

Anyway, because of the small heat load, I'm leaning to keeping the boiler and radiant heat simple. Toward that end, because of me realizing how small a boiler I need, I am considering going cheap, and trying out the Navien 55 boiler (boiler only, no combo) that just came out. It's only $1,600. Now, I normally would never consider going cheap--I tend to like the buy the best brand and best-made for things like cars (which I drive forever) and houses (which I restore to last forever). But darned if the numbers on this Navien don't match my needs.

I also have read that the new mod-cons aren't lasting all that long anyway, like 10-15 years. They're not like the cast iron boilers. So if the high end $3,500-$4,000 boiler is going to last only 10-15 years anyway, why not give the Navien a go? If it lasted 7 years, that would be ok, $ for $.

And for the guys who keep talking about the Manual J math--I have had that done. Twice. By two different boiler contractors here in the Bay Area, and they each came up with two wildly different numbers which they sear by. Forgive me if I didn't make that clear. One was around 100k and the other was a fraction of that.

When I've done the Manual J speadsheet myself, and spend about a few hours reviewing it, I came up with about 31,000 btu. Which is consistent with what you guys are saying. So I am going with a 40k btu boiler (I think). Which doesn't leave a lot of choice other than the Triangle Tube with the 47k output.

I suppose I could put in a cheaper 25-35k cast iron 80-85% efficient boiler, but I really don't want to. I want higher efficiency and a smaller carbon footprint.

Hope that puts to rest the Manual J aspect. And when I do the backwards math I spoke about, I am using ACTUAL fuel use numbers and meter reading rates. You cannot do a whole month out here in CA because the weather is always all over the place, you have to do the specific time period when it's cold and rainy. PG&E in San Francisco has crazy accurate smart meters (they are required) and hourly usage, so it's super accurate and all available online. The fact is, I can go for days and days of cold sunny weather here and nail the usage at 4.18 therms per day, or go for days of rainy weather, which usually means slightly higher air temps, which also miraculously use 4.18 therms. Right now, my boiler is very predictable. I didn't just pull that figure out of nowhere. It's hard to get more accurate than that currently. And also, my former tenants, who burned the boiler up, keeping the house 76 degrees, have numbers which are not useful for my family.

It makes sense considering your ground water temperature, which we would not need to heat for bathing here in Minnesota!

Careful sizing of the new Navien CH240 considering the limited heating output may put you in the sweet spot especially if you don't mind waiting for the tub to fill with "endless hot water". If you have a large tub with a 25 gpm tub filler the water may get cold before you get it full.

In our cold climate the non-storage combi-boilers are hard to fit in many lifestyles.

Manual 'J' is only as good as the operator, but still the standard.

As for modcon life expectancy; the application, installation and preventative maintenance will be the largest factor in the serviceable life of the unit. Most of our 12 different boilers will last 20 years with reasonable care in residential application, same as the tank-less water heater depending on the quality of the potable water and the amount of same run through the unit.

The reason you're getting wildly different Manual-J numbers is probably due to the fact you are letting BOILER CONTRACTORS run the numbers (meaning no disrespect to Morgan, who surely does the calculations much more carefully than typical HVAC contractors.) No matter how well designed the software and calculation methods, garbage-in== garbage-out. Most HVAC folks have a thumb on the scale "just to be sure"to not get the 5AM call from a cold & irate client, or to make the numbers meet the WAG that they feel most comfortable with, but it has nothing to do with the actual heat load.

And that is where sanity checking with fuel-use against heating degree day data is quite valuable. Short of that, when you have competing numbers, the lower number is almost always closer to reality, and still an over-estimate of the real heat load.

You absolutely CAN do a whole month of heating degree data in the SF bay area, or any other place. Heating degree-days are still heating degree-days, even if there was a 3 day period in the middle that had a modest cooling load. The fact that you use 4.18 therms/day under a few varying conditions doesn't really mean much. The average over a whole month, or better yet, a couple of winter months will do an excellent job of putting a very firm upper bound on the actual heat load, using base 65F (and not your interior room temp) as the zero point on the slope. Since you're using gas for other things, and the boiler isn't really delivering it's nameplate efficiency, the fuel use calculation is guaranteed to come in higher than the actual heat load, but most boiler contractors' Manual-Js come in higher than even the source-fuel BTUs. Odds are pretty good that with 5-7 people showering daily, more than half of that 4.18 therms/day went down the drain as ~100F water, not into heating the house.

With 7 people sleeping inside that's 1500-2000 BTU/hr of mammalian auxilliary heating that comes directly off the heat load too.

If you REALLY want a smaller carbon footprint, stop burning fossils, and install a Daikin Altherma hydronic heat pump for heating the floors. Or become an early-US-adopter of the Sanden GAU/EcoCute (soon to be released in the US.) Either of those would have sufficient output for your actual space heating load. (The Sanden would have long recovery ramps from deep overnight setbacks though.) The Altherma would cost something like 10-15 grand, but IIRC the installed cost of the Sanden would come in around $5KUSD (the raw hardware is ~$3.7K, and it delivers about 16,000 BTU/hr in the form of 150F water when it's 30F outdoors, more if you can run with cooler water temps, and at higher outdoor temps. See:

https://www.neea.org/docs/default-source/reports/laboratory-assessment-of-sanden-ges-15qta-heat-pump-water-heater.pdf?sfvrsn=8

http://www.greenbuildingadvisor.com/articles/dept/musings/split-system-heat-pump-water-heaters

These units would average a COP of about 4 in your climate (comparable to geothermal heat pumps), and the carbon-content of the Bay Area grid is already much lower than the national average, and shrinking daily. You'd have to take a hard look at the PG & E rate structures- even at a COP of 4 you're probably looking at adding ~12kwh/day (350 kwh/month) to the electric bill during the heating season (assuming you're displacing about 2 therms/day of gas use- the rest was hot water.)

I couldn't have said it better myself. Really.

I can only add that the heat load software, assuming a Manual 'J' baseline, come in many forms and the trades have little, if any, training in their proper use. Some simply produce the report and go back to grandpa's "Rule of Thumb". If they do any AC they still use a ton/500 c.f. formula from the 60's. Forget about climate, building science et al.

Where a heat load is required at all, as it is here in Minneapolis/St. Paul, the local distributor does the heat load for the contractor, it is submitted to the city and approved.

You must find a trusted, experienced designer to do the room-by-room heat loads for new work and at least a block load for heat source replacement.

And by all means follow Dana's sage advice and flawless math to determine the recorded fuel usage in the historically coldest month.

As Dana suggests, a degree day is the same, just a btu is the same in any location.

And hey thanks for bringing up Sanden GAU/EcoCute, I won't be able to sleep until I get one installed!

Not so fast there, Morgan. Like all of the EcoCute type heat pumps the CO2 unit is self-contained, and the connections between the compressor & tank are water. The Sanden is only freeze-protected down to +14F on the specs I saw, which is pretty much a mid-day temperature in your neighborhood. Some may be good down to -4F (the now discontinued Sanyo was), but even that is a pretty common lo-temp for you.

I'm not sure how badly an antifreeze mix would affect the heat transfer & COP of the thing, but I'm pretty sure the warranty would go up in flames.

But in Girlbird's neighborhood it seems like a pretty good fit. I've been corresponding with an early adopter in Portland OR who is installing one as a heat + HW combi in his PassiveHouse, where the space heating load is less than half his hot water heating load.

OK, maybe when we both retire to the New Cuba...

My conclusion on the Sanden GAU is that if you have access to natural gas, use it.

What inspires your affection Jonr?

The marginal cost of operation of condensing gas in Portland OR (where the guy is installing a Sanden for heat & hot water in a PassiveHouse) would be higher than for the Sanden, a combination of relatively inexpensive electricity and moderate-pricing on natural gas. He too considered condensing gas options, but preferred the low carbon aspect of heat pump solutions (the grid there is nearly all hydro), but not the high-cost of the Altherma. The Sanden's output is big enough to fill the heat & HW bill for him with a lot of margin and the installed cost is expected to be about 1/3-1/2 the cost of an Altherma solution.

The operational cost numbers will be different in girlbird's neighborhood due to the step block rate steps for power us. It may still be favorable to natural gas (or not), but that wasn't the point. The stated goals for girlbird were:

"I want higher efficiency and a smaller carbon footprint."

A COP of ~4 and an already pretty-green (and getting greener daily) grid is higher efficiency and lower carb than site-burned natural gas. Even if the local power grid in the Bay Area was 100% natural gas (which it isn't) it would still be lower carbon emissions per MMBTU of heat delivered to the house than a condensing gas burner.

Clearly jonr's goals may be different.