Getting ready to build approx. 5000 ft ICF home w/ radiant floor heat.  I have to use propane or wood for my heat source.  I dont want to cut wood forever, so which is more efficient, water heater or boiler.  Any advice would be appreciated

A (efficient) boiler. We're researching our own house and boiler seems the way to go. The boiler would heat the domestic water as well as part of an indirect-water-heating system. ...5000sft! big ass house :)

mod/cons are the most efficient choice. House your size, that should be the choice unless you are only periodically using the backup.

If you don't want to cut wood "forever" but it will be several more years before you anticipate slowing down, maybe you want a cheap source now and replace later with something more efficient.

We would recommend a LAARS Neo Therm modulating condensing boiler probably a 150,000 or 200,00 BTU unit depending on location and domestic H20 needs. Boiler would be coupled with a Stainless steel side arm tank for domestic water loads, 40-80 gallons is about right for a house your size. May want to plan for future solar preheat if possible as an option down the road.

Forget a water heater.
Dan

that boiler is probably twice the size you actually need with a 5k sq ft ICF house. this is a small part of why real load calculations are important.

Did someone say ModCon?

Where are you located,
Boiler size can be de rated 25% if forinstance you are in the 6,000 foot elevation,
Perhaps in your 5,000 square foot home you have a combined bath room DHW loads that can consume 400-500 gallons per hour, that to can affect boiler size,
150-200,000 BTU is in the hunt with a 5,000 sq foot pad, keep in mind a modulating boiler will only ramp as needed.
100,000 BTU will drive approximately 3 GPM of domestic plus storage in your tank
Dan
ModCon...Mod Con

Last I knew it was 2% per 1000 feet de rating.

5,000 at an average 20 BTUs/sq ft.. almost certainly high, probably close to double reality for ICF of this size... is 100,000 BTUs. I'm pretty sure a 5k square foot house has never been built after 1970 that averaged much higher than that. raising your output only increases cycling and reduces efficiency for no real benefit. For ICF I wouldn't be surprised if his average load was 10 BTUs/sq ft, frankly.

Increase the size of your indirect if needed, but size the boiler appropriately. If you have bigger domestic demands, then maybe a different tactic is needed, but that tactic should never been "jack up the boiler size and proceed as normal".

This is a cut and paste from an article on high elevation engineering. link http://www.esmagazine.com/Articles/Cover_Story/BNP_GUID_9-5-2006_A_10000000000000020238
It supports a derate of 4% per 1,000 feet.
Agreed a larger side arm is fine, replacement capacity of the boiler, 80 gallons plus 3 gpm or less on a 100,000 BTU appliance seems light for a larger residence. I would be looking at 150,000 BTU and be pleased with surplus capacity even at sea level. A typical 5,000 sq ft home may have 3 plus full bath plus associate laundry, and kitchen needs.
But then I have no clue as to this design or location, just the concept.
Dan

Gas-Fired Equipment
Equipment utilizing an atmospheric burner must rely on the buoyancy of hot combustion gases to induce the proper amount of air into the combustion chamber. This is roughly a constant volume process, and with air at altitude having less mass than at sea level, the result is less mass flow rate for a given flue temperature. Consequently, a gas-fired heating apparatus will yield less output at altitude. For elevations above 2,000 ft, ratings should be reduced 4% for each additional 1,000 ft above sea level.

To compensate for reduced combustion air mass flow rate, the gas flow rate must also be reduced. This can sometimes be accomplished at lower altitudes by simply reducing the manifold pressure, but at higher altitudes the burner orifice size must also be changed.

With forced-draft equipment, burner fan capacity is increased to compensate for the thinner air. Equipment manufacturers often offer larger fan and motor packages as options. Compounding these issues is the fact that at an elevation of 5,000 ft, the heating value of natural gas is only 850 Btu/cu ft at the burner due to reduced atmospheric pressure instead of slightly over 1,000 Btu/cu ft at sea level. Certain gas suppliers in mountainous regions may provide an enriched fuel that has a heat content greater than 1,000 Btu/cu ft. Larger fans and motors will often increase furnace pressures to the point where it could impede the flow of fuel to the burner manifold.

Typically, a higher gas flow rate is also beneficial because of the lower heating content of the fuel, which requires higher pressures at the inlet to the gas train. If higher pressures are not available, then larger diameter piping and components are required throughout the system, from the fuel source to the gas train and burner ring.

The effects of high altitude affect not only the gas-fired equipment itself, but also the associated chimneys and flues. For a given input, an appliance operating at altitude would need a larger flue way than one at sea level. A simple method of determining flue size is to correct the appliance input rating for altitude and then proceed to the sea level design charts. The altitude correction for this approach is the ratio of the air density at sea level to that at altitude.

Thanks for sharing that Dan. Info I had read previously wasn't that aggressive. I wonder why the discrepancy, but it's good to know that there is some difference in the de-rating out there.

Thanks for all the reply's and helpful info. I am located in Indiana. Thanks Again!

Thanks for posting this and valuable information. Thank Again !!











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Electric Heater