Our propane whole-house system is a high efficiency (95.5%AFUE rating) propane system made by Tempstar but there are other manufacturers of this style of high efficiency furnace out there to choose from. Again, we usually just heat with our wood stove but the whole-house unit is available when desired.
For our 460 square foot guest house, the direct-vent propane heater can be vented through the roof and does not require installation against an exterior wall. This heater is a Hampton H15. The vent pipe seen here is a concentric pipe where the a smaller diameter combustion-air pipe runs through the center of the exhaust pipe.
This heater is one of the smaller ones out there but it’s perfect for heating the small space that it’s in. Though ours is against an exterior wall, it can be installed along an interior wall and vented through the roof (up to 30 vertical feet) instead. Here’s a pic:
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Thank you for sharing this info Spartan. I've been doing a bunch of research and a few things standout (that this fine group has called out a few times in this thread already.)
1. I am going to have to implement multiple solutions. I was made aware that a recent storm kept panels covered in snow until they were cleaned off, which I won't have the luxury of doing quickly.
2. Propane is going to have to be one solution - Unless we do a monster battery bank, which just doesn't make sense (see above)
3. Anything we can do now from a design perspective in order to retain as much heat as possible will pay off in spades over the life of this cabin.
Option #1: Second favorite, as it's primarily reliant upon propane, but it's probably a better option in my situation.
- Propane condensing boiler for radiant heat. I looked at electric boilers, but the draw is too high.
- Mini-splits for back-up heat
- Mini-splits will provide A/C (wasn't a priority, but nice benefit for the 2-3 weeks when it might be used)
Option #2: Would be my first choice, but I'm not confident on energy requirements.
- Air to Water Heat Pump - for radiant heat only. DHW with HPWH
- Propane direct vent heaters
- No A/C
- FUTURE - we could do "home runs" to each room for future use of wall mounted distribution for any A/C needs
Feel free to blow holes in either of those options!
I've been using ChatGPT as well. I believe the dataset is current through late 2021, so some of this might be outdated, but it "feels" accurate to me. I was researching electric boiler needs and air to water heat pump electrical needs. I realize I don't know the true heating load of this property yet. The heat pump wins out big time in this assessment, which is not surprising.
You said:
What would be my electrical needs for the electric boiler in a typical heating season at my cabin?
ChatGPT said:
To estimate the
electrical needs of an electric boiler for your cabin during a typical heating season, we'll consider several factors:
Key Inputs for the Calculation
- Cabin Size & Heating Load:
- Total area: 1,800 sq. ft.
- Open kitchen/living area: ~1,100 sq. ft.
- Climate Zone: 5b (cold winters with moderate heating requirements).
- Estimated Heat Demand (BTUs):
- A Pretty Good House standard typically requires 10-20 BTUs/sq. ft. per hour for heating.
- For 1,800 sq. ft., the heat demand is:1,800 sq. ft.×15 BTUs/sq. ft.=27,000 BTUs/hour.1,800 \, \text{sq. ft.} \times 15 \, \text{BTUs/sq. ft.} = 27,000 \, \text{BTUs/hour}.1,800sq. ft.×15BTUs/sq. ft.=27,000BTUs/hour.
- Electric Boiler Efficiency:
- Near 100% (1 kW = 3,412 BTUs).
- Heating Season Duration:
- ~6 months (October to March) in central Utah.
- Assume 10 hours/day of heating on average.
- Electrical Energy Use:
- Total heating hours: 6 months×30 days/month×10 hours/day=1,800 hours.6 \, \text{months} \times 30 \, \text{days/month} \times 10 \, \text{hours/day} = 1,800 \, \text{hours.}6months×30days/month×10hours/day=1,800hours.
Step 1: Convert Heating Load to kW
- 27,000 BTUs/hour ÷ 3,412 BTUs/kW = 7.91 kW/hour.
Step 2: Estimate Total Energy Use (kWh)
- 7.91 kW/hour×1,800 hours=14,238 kWh/season.7.91 \, \text{kW/hour} \times 1,800 \, \text{hours} = 14,238 \, \text{kWh/season.}7.91kW/hour×1,800hours=14,238kWh/season.
Step 3: Daily and Monthly Use
- Daily Use: 7.91 kW/hour×10 hours=79.1 kWh/day.7.91 \, \text{kW/hour} \times 10 \, \text{hours} = 79.1 \, \text{kWh/day.}7.91kW/hour×10hours=79.1kWh/day.
- Monthly Use: 79.1 kWh/day×30 days=2,373 kWh/month.79.1 \, \text{kWh/day} \times 30 \, \text{days} = 2,373 \, \text{kWh/month.}79.1kWh/day×30days=2,373kWh/month.
Key Considerations
- Solar System Sizing:
- Ensure your solar panels and battery bank can handle the daily/seasonal demand.
- Winter has less solar production, so you may need backup or additional storage capacity.
- Thermal Storage:
- Adding a water-based thermal storage tank could help run the boiler intermittently, reducing peak electrical loads.
- Supplemental Heating:
- Consider using passive solar heating, a wood stove, or high-efficiency heat pumps to reduce boiler dependency.
- Energy Efficiency:
- Additional insulation, airtightness, and high-performance windows can further reduce heating loads.
How many watt hours per day would I need?
ChatGPT said:
To estimate how many watt-hours per day you’d need to power an
air-to-water heat pump for radiant heating in your cabin, we can calculate based on the following:
Assumptions
- Heating Load:
- Your cabin's heating demand is 20,000 BTUs/hour on average.
- Heat Pump Efficiency:
- A cold-climate heat pump has a COP of 3.0, meaning it uses 1 kWh of electricity to generate 3 kWh (10,236 BTUs) of heat.
- Daily Operating Hours:
- Assuming the heat pump runs 10 hours/day to meet heating needs.
- Electricity Conversion:
Step-by-Step Calculation
1. Energy Needed per Day (BTUs)
Heating load × daily runtime:
20,000 BTUs/hour×10 hours/day=200,000 BTUs/day20,000 \, \text{BTUs/hour} \times 10 \, \text{hours/day} = 200,000 \, \text{BTUs/day}20,000BTUs/hour×10hours/day=200,000BTUs/day
2. Electricity Needed (kWh)
Divide total BTUs by the heat pump efficiency and conversion rate:
200,000 BTUs3.0 COP×3,412 BTUs/kWh≈19.6 kWh/day\frac{200,000 \, \text{BTUs}}{3.0 \, \text{COP} \times 3,412 \, \text{BTUs/kWh}} \approx 19.6 \, \text{kWh/day}3.0COP×3,412BTUs/kWh200,000BTUs≈19.6kWh/day
3. Watt-Hours per Day
19.6 kWh/day×1,000=19,600 Wh/day19.6 \, \text{kWh/day} \times 1,000 = 19,600 \, \text{Wh/day}19.6kWh/day×1,000=19,600Wh/day
Result
You would need
~19,600 watt-hours (Wh) per day to power an air-to-water heat pump for your radiant heating system.