Heating Options at high elevation in cold climate

Question

Currently designing a 2500sqft house in the Sierra Nevada mountains at 6300ft elevation. It's an A-frame with a loft and living room area has high 20ft ceiling peak. It snows 4 months of the year, and summers are moderate with one or two 90˚ days. So I'm going to forego cooling, but considering options for primary heating:

• Electric Radiant flooring: I was planning to use this for bathrooms under tile anyway, but why not just extend to the whole house? I drew up a plan to lay about 820sqft of resistance wire mats through out the house totaling 10kW of power. I estimate the total cost would come out to $12k installed.

• Traditional Forced Air Central System: No access to gas, so this would be electric too, probably sized around 3 Ton, which would be around 10.5kW. This will certainly cost me in the $20k range installed.

• Heat pump system: I was advised heat pumps would not perform well at this elevation and climate where temps go below freezing for a significant part of the year.

I'm drawn to the electric radiant heat idea. It seems more efficient because of direct heat delivery as opposed to duct losses with a forced air system. I'd also be able to have multiple zones individually controllable. QuiteWarmth system

In the above described scenario, are there any other pros/cons to consider? Or suggestions on other energy or cost-efficient heating sources where natural gas is not available?

Edit 1: More specific question to make this less open-ended. Here's an electric radiant floor mat layout plan I drew up for the living floor, which is about 1800sqft. Is 9.8kW worth of heating enough for this area?

Edit 2: Thanks for all the great answers and comments. Did a ton of research to get ball park numbers into a spreadsheet to understand how much it will cost and what is the breakeven point vs plain electric.

Two critical inputs are the heat pump efficiency at different temperatures. I looked through the manual of a 28kBTU copper+hunter unit and pulled out some COP figures that seemed reasonable. But it provided for heating:

• COP @ 47F outside ~ 3.7
• Rated capacity at 17F ~ 17kBTU
• Max capacity at 5F = 21kBTU

Question 1: Why would the max capacity be higher at 5F compared to rated capacity at 17F? What is the difference between rated and max capacity?

Question 2: I assumed COP @ 47F is 3.5 and COP @ 17F is 1.5. Are these reasonable estimates?

Question 3: Very hard to find COP vs outside temp charts for most available units, so what average figure can I assume for COP @ 5C for example?

Question 4: Finding that it will take roughly 4-7 years to breakeven on the investment required for either heat pump or propane. Is this what one might expect vs going purely electric, or am I being too optimistic here with incorrect assumptions?

Answer 1

Total Cost of Ownership

While I am sure you are investing plenty in your dream house - and that's a great thing to do - since you actually bother to mention cost of installation of different systems, you are at least a little concerned about cost. So look at the total cost. That's:

• Installation cost amortized over expected system lifetime
• Running cost - calculated by cost of fuel x hours per year (or similar, there are multiple ways to do it but the results are roughly the same)

Since all of your proposed systems are electric, it comes down to resistance heat (whether radiant or central forced air) vs. heat pump. We already know some key numbers:

• Installation of radiant = $12k
• Installation of forced air = $20k

We don't know installation of a heat pump. My guess is that it would be a bit more than an electric resistance forced air system because (if central/forced air, though there are other options that might work) the outside parts of a heat pump will add significantly to the total cost. So let's guess $25k - but it could be more, I don't really know.

Running cost for radiant and forced air will be based purely on electric. Not surprisingly, they are nearly the same - 10 kW vs. 10.5 kW. In fact, I would expect the forced air system to use just a drop more than equivalent radiant heat because it takes electricity to run the fan. But we are talking about a 5% difference - basically noise.

However, a heat pump can easily achieve a significant improvement in efficiency, measured as COP. That number can easily be 2 or more, but it does generally decrease as the outside temperature decreases.

What we also don't know is how many hours your heat will need to run. If, for example, it runs 6 hours a day for six months of the year and 2 hours a day 3 months of the year (cold at night) and not at all for the hottest 3 months then you have:

• (6 x 6 x 30) + (2 x 3 x 30) = 1,080 + 180 = 1,260 hours

Next we calculate the energy used:

• Radiant = 1,260 x 10 kW = 12,600 kWh
• Resistance Forced Air = 1,260 x 10.5 kW = 13,230 kWh
• Heat Pump estimate COP 2 = 13,230 / 2 = 6,615 kWh
• Heat Pump estimate COP 1.5 = 13,230 / 1.5 = 8,820 kWh

and then we apply an electric rate. It varies a bit, for now I'll use a nice simple $0.20 / kWh

• Radiant = $2,520 per year
• Resistance Forced Air = $2,646 per year
• Heat Pump COP 2 = $1,323 per year
• Heat Pump COP 1.5 = $1,764 per year

So it is quite plausible that a heat pump could save $1,000 or more per year. Meaning if you have an expected lifetime of 10 years (which I think is conservative but repairs do start to add up as well in later years), you could easily save $10,000 or more which would offset, and possibly exceed, the initial extra cost of a heat pump system.

So to proceed sensibly:

• Try to determine how much your heat will need to run - heating degree days (which you can't control), insulation (which you can control) and other factors affect this quite a bit.
• Get a couple of quotes on a heat pump system for the house to compare initial costs.
• Determine COP based on heat pump specs combined with historic average temperatures for each month and then calculate an average COP for a "typical" year.
• Find out local electric rates and whether they tend to be stable or fluctuate a lot.
• Put it all together to determine TCO for each option.

There are other advantages/disadvantages to consider. Some people prefer radiant heat (warm floors), some prefer the hot blowing air of a forced air system. Radiant heat should be nearly maintenance free. A forced air system will have a blower, a heat pump will add quote a bit more active equipment. Make sure to factor expected equipment lifetime - vendors should be able to give you a rough idea even though nothing is generally guaranteed for more than a year.

Answer 2

Ah, you veered close to an answerable question - I'll run with it.

Whether any given amount of heating is adequate for a given space depends very much on the insulation of that space and the design-day temperature (which is either as cold as it ever gets there, or as cold as it gets there "normally" and on super cold days there should at least be enough heat the pipes don't freeze, [since design is typically for 68°F / 20°C inside temperature] and then it returns to the normal range.)

With zero information about the insulation or the actual design temperature, ("below freezing" offers a very wide range) the proposed amount of heating may be too much, not enough, or just right. Based on what look to be sliding glass doors, there are some large areas of poor insulation, and that requires enough heat to compensate for them dumping it outside.