Low heat loss: Best powerplant?

Mike Dunn

I constantly struggle over what to use for a heat source when the heat loss is between 0k and 30K. It seems a regular boiler would be overkill, but using a water heater just doesn't seem right either. I generally will use a tankless water heater when there is no domestic needs, and a tank style when there are domestic needs. I sure would like to here some other thoughts and suggestions.
Thanks

Brad White_98

Good Question

It was recently mentioned that a low-Btu Munchkin design may be forthcoming.... a good thing in that boilers will finally come down to where heat losses have been heading lately...

That said, a closed circuit application of a domestic water heater is something I have applied before with good results. No modulation of course and there is that standing pilot. I do not use these routinely (indirects being King and all) and the newer models may work better with different ignition types if not modulation. Still a low cost way to get radiant floor heat or other low-temperature applications.

DHW heaters are not boilers per se, but seeing as they are rated for 150 psig and can take raw water from 40 to 140, running them at 12 psig and recirculating deoxygenated water, the simply have to last a much longer time than their listed application. My first, installed in the early 1980's was still running as of about five years ago. My big reservation is that unless they have a means of ignition other than a pilot, you cannot shut them down as in a runaway situation... Mmmmm.... Maybe a Taco WAGS valve may have an application here? Let me think about that...

If not centralized and if an open plan layout, direct-vent space heaters like the Rinnai RHFE series or Monitor GF-1800 may work well. The Rinnai have lower inputs for better distribution and have a wider range of sizes. Not the same as radiant floor heat but my friends with cabins in the woods swear by them. Why not year-round?

My $0.02

Scott Gregg

Why not...

Why not use a tank water heater or a tankless? A btu is a btu and a water heater will do a fine job of making hot water for a radiant system. I have even seen electric tankless heaters used with good results in these applications. I would have no problem specifying/installing a water heater on a small demand radiant system.

hr

Sources tell me,

there are some other mod cons on the way in the under 50K input range. I'd like to see a40 K for water heater sized replacement jobs.

After witnessing mod on savings over a heating season, on my own system, I think these could be an easy sell to upgrade those tank style water heater systems. And there are thousands of those water heater systems out there.

Also pairing up two 40 K mod cons would provide a VERY desireable turn down ratio 10 to one for a possibly 10 K low output to an 80K high side with 10 steps in between. SWEET!

I buy two 40K's before one 80 in a heartbeat. If for no other reason REDUNDANCY. Especially on my distant installs. those are the ones that breakdown mid winter, generally

Bring 'em on. Wall hung would be my first choice.

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GMcD

Electric heater/boiler

Why not look at small electric sources, easy to integrate with Photovoltaics and a battery pack, get off the grid, and you can have a choice of direct electric heaters/radiant floor mats, electric radiant ceiling panels, etc. or small electric boiler/heaters for a hyrdonic system.

Dale

2 small ones

For max flexibility why not 2 little on demands like the takagi Jr. One for heat one for domestic. Should the heat supply one fail in winter break the unions or have valves set to switch over. For really insulated houses 20K heat loss say, I like radiant mats and thick concrete in the basement, mats under available tile and good quality elect. baseboard for heat. Individual room control and really simple.

LarryC

Electric heat on PhotoVoltaics???????

PV at BEST is about 1.2x the cost of buying electricity from the power company. Start adding the inefficiencies of low voltage to 120 or 240 volt inverters, the cost of batteries, maintenance, and replacement every 10 years.

PV is not economical to heat water. It is like buying a Rolls Royce so you can use the exhaust to blow up party balloons.

LarryC

[Deleted User]

HR...

What kind of savings did you see?

Just curious.

ME

GMcD

Hey, it's an option

The other option is to use solar water panels and a storage tank setup. The PV and electrics is a good option depending on how one sees the long term electricity costs rising- don't forget that a lot of the electricity out there comes from fossil fueled thermal power plants, and that won't be getting any cheaper either.

Unknown

under 20k, and I'd see a tank water heater as the simplest, cheapest way to go, dedicated of course or with an HE for dual use.

No high head pumps, no tricky piping, at that load you probably have a very small water temperature range, so maybe even a 3-way tempering valve to set the radiant temp or the water heater's aquastat itself. Or if you're doing dual use, you already have the piping/pump to do variable speed injection pretty cheap.

Up around 30k I still favor the smallest Munchkins or Ultras, with their sub 20k turndown, it's not bad. and if it's acting like a sub 20k burner when it's below that, well, you're not that oversized.

Depends on the degree day count a bit too though. If it's 30k max in michigan, then go small mod/con. If it's 30k max in South Carolina, then go water heater, the mod/con will never pay for itself.

Just MHO, of course, but that's how I look at it.

hr

An honest 30% fuel reduction with Knight

on duty this past winter. True it was a milder than normal winter. One nice feature on the Knight is the data logger that spits out run time hours both in the heating and dhw mode.

If only the old cast iron boiler had that I could crunch some better numbers.

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hr

Use caution with tank styled WH's

if it is gas, lp or oil fired. They really are not designed to run low radiant temperatures (condensing models excepted)for extended periods. You WILL rust out the baffles and HX, which can sprinkle down on the burner and cause incomplete burns and at worse case CO issues.

Really need to run them 140 and use a mix valve for the low radiant temperature in my opinion.

Of course by the time you PS pipe them use two circs and a mix devise, you are half way to a small mod con cost. And it is a legal, listed heating appliuance.

Don't put them to bed wet on every burn cycle.

Also I think those mid 70% efficiencies presented by DHW tanks should be a thing of the past with fuel costs.


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Unknown

I'm considering fuel costs; on a really tiny load, the amount of difference that makes gets smaller and smaller. depends on climate as well as design load though, of course. A $600 water heater has a lot of ground to make up compared with a $2k boiler. Plus the beauty of hydronics is, if things really go nuts, you can always switch later and you're only out the $600 for the water heater and a few bucks in fuel. I'm an efficiency nazi as much as the next guy, but sometimes cost needs to be considered along with benefit

[Deleted User]

Hind sight...

is ALWAYS clearer.

Your 30 % falls right in line with what I saw with my Munhckin T-50, what my partner and Dennis Bellanti saw with their GB's and pretty much what we see on a regular basis. 30 % is the minimum, and some rise up to 50% fuel reductions.

Thanks for responding.

ME