[postscapes1]

Just as a heads up. Make sure you get a real pro to do the sizing on your unit.

I put in two Mitsubishi H2i systems last year and have had some pretty insane energy bills due to sizing them too large (A general overview of why here: https://carbonswitch.com/heat-pump-sizing-guide/)

Once I get my solar in place I won't feel too bad about this, but for now has been a bummer as was expecting a real efficient beast.

[dtgriscom]

Around here (NE USA) oversizing is common with furnaces; the attitude is "better safe than sorry" where "sorry" means "contractor gets called because furnace struggles in mid-winter".

I replaced my old (95kBTU/hour output) forced-hot-water furnace and separate hot water heater with a condensing furnace about eight years ago. I got a heat loss calculation done, which concluded I only needed 59kBTU/hr of heat. It was a struggle to get a small-enough furnace installed; one contractor said he couldn't in good conscience sell me anything smaller than 120kBTU/hr.

My final system was 89kBTU/hr. A couple of weeks ago, in record -13°F/-25°C cold and high winds, it was burbling along at 60% power. Could have been even smaller.

[bradfa]

We had an energy audit done a few years ago and the conclusion was that we needed about 40kBTU/h of furnace (upstate NY). We have an 80 (came with the house when we bought it). It’s actually quite hard to buy any gas furnace smaller than 60. But modulating gas furnaces seem to be becoming a thing now which is good and may make up for over sizing.

[nicpottier]

If you are oversized you may also run into problems of short cycling in warm weather, where you won't be able to dehumidify because it will be cooling too quickly. Who installed your system, they should be on the hook to fix it.

[thehappypm]

The article doesn’t make it seem like oversizing is a problem for efficiency —- it will just cause the units to turn off more frequently, leading to other issues.