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Heat Pump Hot Water System vs Gas Hot Water

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EEVblog:
Comparing gas hot system to a heat pump hot water system before I install a Reclaim 415L heat pump hot water system at home.

SeanB:
Quick tip before you cut over, measure temperatures of hot water outlet and cold water input. Likely gas heater keeps that tank at 90C plus, while the heat pump works best as a heater to around 60C Most use you blend hot and cold, so for a shower you probably blend around a third of the hot water with two thirds of cold water, likely at around 18-20C, to give you the 40C or so shower water. Same for the sink, hotter than 40C will burn.

So take into your calculations for water use that dropping the temperature ( over 70C heat pumps drop drastically in COP, a hidden figure, just like Peltier coolers there is a very steep curve) to around 60C will result in you using probably equal amounts of water from both, so the heat pump tank is now about equivalent to the gas heater.  Same total volume of water used, just different settings now on the shower mixer if single lever type, and same for sink.

Best added thing to do is go and install insulation on all the hot water pipes, both inside the roof and outside, so that you do not lose that expensive heat, as you can easily have a 10C or more loss along a long run, especially at low flow. You pay money for that heat, why throw it away heating up the attic, it generally is hot enough already, and you are not going to get more heat into it, so insulate. Insulation is cheap, and you get zip up types as well from the industrial AC suppliers, or just the regular slip on black neoprene and slit it, then use the tape to close it up. $2 per 2m length, a tiny cost. Also on the first 1m of the inlet pipe, as you will see the greatest heat loss is those inlet and outlet pipes, along with the mandatory pressure and temperature relief valve. Water best to install pressure control for the whole house if you do not already have it, balanced hot water system is a great thing, no fighting if somebody flushed the toilet and the shower flips cold boiling cold a few times.

ssander:
Just checked my councils noise restriction times. Times for heat pump water heaters are more restrictive than AC units.

Fortunately you're going to run it during the day. Although if you have showers at night, it'll probably want to kick in at night and reheat the water in the tank.

SeanB:
Not really needed, simple enough to just leave the tank to heat up the next day when power is available, and the sun can provide it. I did find that insulation works wonders, with adding extra insulation helping a lot in holding the water hot. I did accidentally find out, by messing up the timer setting, so it was left in the off mode (tiny little switch that moved to wrong position when closing the cover), and I only noticed 3 days later on that the hot water was now coming out merely warm, and tending to cold.

This on a 100l standard electric hot water heater. biggest gain on any stored heat system is improving insulation, and Dave should, before hauling the old one out, take one of his thermal cameras and look at all the heat leaks in the gas system, especially with just a trickle of hot water running at the furtherest tap in the system, and use this as a guide to insulate the system a lot better. My one is a big ball of green fluff, recycled PET bottle insulating batting, normally used in drywall as insulation, but I had a part roll around from repairing a drywall section at work, and as the add on is the same stuff with a fancy quilted cover, I just finished the roll. Also insulated the hot and cold pipes as well, as far as possible till they hit brickwork, and only drawback is now the cold tap has a slug of warm water when first opened. The copper pipes condust heat that 2m length well.

Dread:
This might not be what your expecting.  I do not know the model your getting but if it's anything like the Rheem models they sell in the USA the noise from the compressor is going to drive you crazy!
The Humming sound is so loud (70db) that you can hear it in almost any room in the house and it's super annoying.  They claim it's 41db but it's not!

Second issue is that it they are easily burned out by power outages and surges.

If this is a free demo unit then great but if your paying the full price I highly suggest that you get some sort of guarantee on the Sound level or you will be defaulting to using only the elements just to keep your sanity.

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