Heat Loss vs Heat Pump Ratings
rshuman
| Posted in Energy Efficiency and Durability on
Given an estimated heat loss rate, how should the listed capacities for heat pumps be used to select a unit that is capable of meeting my heating needs.
For instance, given a heat loss rate of 18,000 BTU/h for a house where the design temperature is 1 deg F, should I ensure the maximum capacity of a given heat pump at a temp close to my design temp, say -5 deg F, is approximately equal to the estimated heat loss? Or is that approach too conservative (given the small probability of those temps occurring) and likely to cause me to oversize the unit? And if it is too conservative, what are some reasonable alternatives.
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Replies
Your operating cost won't go up much if the heat pump doesn't quite meet the Manual J load and you use supplemental resistance heat to make up the difference.
On the other hand, fully meeting Manual J load (at design temp) or slightly exceeding it per Manual S isn't "over-sized", at least for heating.
In either case, you are likely to have problems if the heat pump shuts off from being too cold (below design temp). Or even if output drops significantly - such weather happens, sometimes for extended periods. Consider 100% backup heat.