I am trying to find the most cost effective means of heating my small house, zone 5 elevation 7k, calculated heat loss ( with hvac calc, no fudge factor added) at 21 k , approx 1100 sq ft  fairly well constructed. I have narrowed it down to  1) small mod con with low boy indirect  or 2) condensing water heater which could run both the dhw and myson panels.  My concerns are there doesnt seem to be many boilers which are built for small heat loads- munchkin 50 size.  I do like the thought of using one system to run both domestic and space heating.

                          what do you think
 
                                Jerry

With a heat load that small mod-cons don't make a huge amount of sense. A B & W combi-2 or a condensing HW heater with a small hydronic loop or something would get you there.

If it's a propane-fired system you may do better with a mini-split heat pump in zone 5, combining heat & AC systems rather than heat & HW systems.

I tend to agree with Dana. Look into a Polaris or Vertex or Phoenix Water heater. Then you can add the hydronic loop and you will be a happy camper.Solar preheat would also be a nice add-on.

Hello all,
Myson, great product but keep in mind they are not potable rated and are steel units, they will need a separate heat exchanger coil. this meens that the Vortex, Polaris (not sure about Phoenix ) will need a heat exchanger and pump for radiator load.
Keep also in mind that at 7,000 foot elevation there is a de rating of the appliance, 100,000 BTU - efficiency - about 20% for altitude.
So the mod con is looking like a smart choice as 125,000 btu unit (Mascot 2) will turn down to a low BTU but will have the resource in BTU to ramp up and provide the domestic side. Plus the radiant loop is isolated via heat exchanger from the domestic h20, as well as a complete control package built in and exp tank.
All this must be added if a person goes with a water heater. There goes the savings.
Dan

I don't think the condensing water heaters make much sense on such a small load. I'd second the combi-2 recommendation. much more cost effective.

Putting a 125kBTU boiler on a 21KBTU max load is... questionable.... at best. the guy's max load is significantly under the Min Mod on that boiler... cycle city. Any tank system would be vastly superior for DHW performance as well as heating efficiency and longevity as well.

This might be a good case for the Daikin Altherma heat pump too.... combine Heat, AC AND DHW, why choose? pricier up front but by the numbers most people are buying at, propane is a dead choice unless your electric rates are through the roof, you have huge on site storage so you can buy in bulk, or you aren't living there long. the Minisplit idea dana had might be better if you have a very open floorplan, but I do prefer hydronics for nearly everything else.

Rob: There are a few places in zones 4 & 5 (most in the NYC area & Long Island) where electricity rates are indeed through the roof- high enough that condensing propane can be a tossup with an inverter-drive air source heat pump. With natural gas it's usually a no-brainer unless electricity rates are exceptionally cheap.

My expectation for future electricity vs. propane price would still favor the heat pump solution. (I'm not sure why I wasn't immediately thinking "Altherma", as you did, but that's probably a win-win-win proposition.)

jlc25: You say you're in zone 5, but at an altitude of 7000'. As a sanity check on weather data, can you share your zip code with us? Not all of zone-5 was created equal from an outside design temp point of view, especially at altitude. If your design temps are below -5F it may limit your heat-pump options, or require separate resistance-electric or other systems for backup.

Condensing water heater with a plate sub-system but gives you sealed combustion, quiet operation and no outdoor air required. Smart choice, and the output is not the key with a tank type condensing water heater. Combi II no, Combi I yes, but pricey for a 80% efficient water heater and must have combustion air. Domestic hot water and space heating in a 22" diameter foot print...I love it!

Long term the Combi's have been spotty on heat exchanger and tank reliability. I like the Vertex and they have the best wholesale support in most areas. More expensive upfront but I think the better value in the long run