Real-Pierre-Delecto2 t1_isujwr1 wrote on October 18, 2022 at 8:21 PM

Reply to comment by skiitifyoucan in Is wood cheaper than oil? by wholeWheatButterfly

I would never trust that 200% number first it's kinda impossible free energy and all that. Yes I know they dont include the air as an input of cost. The 200 number would be under the absolute most ideal conditions possible. Colder it gets the worse it gets.

gmgvt t1_isuptm7 wrote on October 18, 2022 at 8:58 PM

It's not impossible or "free energy:" the issue is that the way your space is heated is completely different and it's hard to understand/explain for people new to the tech. The heat pump is not producing heat like an oil or gas furnace do, hence why their efficiency percentage can never go above 100%. It's circulating colder air out of your house and warmer air in (yes, the design of the evaporator/condenser is such that it can do this even when it is below freezing outside). So the 200% number, or even higher for top-rated models, is accurate. But you're right that the efficiency rating can drop in colder temps and also depends on how well your house is insulated. My heat pump heats my 1980s condo-boom condo very nicely (and more evenly than my Rinnai gas heater) in fall and spring and on warmer winter days, but when temps get down into the teens I start to notice a dropoff in performance so I switch to the Rinnai. Improved insulation and a newer model would probably improve that to the single digits or even just below zero.

RatherNott t1_itenmwl wrote on October 23, 2022 at 1:48 AM

Modern heat pumps from Mitsubishi have such excellent efficiency, they're able to produce heat down to -22f.

To learn more about heat pumps, how they work, and why that 200% efficiency claim is actually true, I recommend checking out Technology Connections video on the subject.

Real-Pierre-Delecto2 t1_itg26aw wrote on October 23, 2022 at 11:33 AM

Well aware thanks very much. What you are ignoring as that while yes they will make heat at -22 they do it very inefficiently. Plenty of charts out there that show this. Or just ask someone who has one how they work at that temp and you will get the same answer. Not all that great or maybe ok for supplemental.

RatherNott t1_itj1amr wrote on October 24, 2022 at 12:20 AM

That's true, but I would argue the efficiency with those latest units make them viable for most households in Vermont as the main source of heat for the majority of the winter/fall/spring, as the amount of days where it is truly cold enough to make a modern heat pump struggle are so few, one could easily switch to a back-up source of heat for those, yet still gain the efficiency gains for the rest of the year.

Real-Pierre-Delecto2 t1_itq5or1 wrote on October 25, 2022 at 2:26 PM

Not to sure about most as we have lots of older poor housing stock here. That's lots of poorly insulated homes and what comes with it. I do think they are better utilized in a newer home that is much better insulated however lots of people get these as a way to save cash in an older home or much larger area than they are rated for and become disappointed pretty quickly. Even with the rebates. At least we have not had the electric rates double like Mass and NH and have. Double the heat bill right there ouch.