DHW: Gas vs "Hybrid"

Larry Weingarten

Hi @Icarus , I'm thinking your idea could work, but I'm a fan of "elegant simplicity", and that approach sounds a bit complex. It's been studied and heat pumps with bigger tanks outperform the same heat pump hooked up to a smaller tank. EF goes up AND you get more hot water. Might that be a simpler fix?

Yours, Larry

ps, How about having the heat pump play backup to a solar thermal system.... or simply have a tempering tank in a warm place to preheat water going into the heat pump?

ethicalpaul

In my last house I did put in a tube solar panel on my roof with a nice controller that circulated its loop to a tempering tank. It was cool but I think the payback was probably 15 years 😂

super_snop

I have the rheem hybrid unit in my unfinished basement for a little over a year now. Basement gets a bit chilly in winter (around 50 degrees) and the heat pump still works flawlessly. I have never taken it out of heat pump mode. The recovery rate is significantly slower in heat pump mode then full electric mode. With that being said, if you do go hybrid make sure you oversize your tank to compensate. My house is a family of 3 and I went with the 80 gallon. Have never had a problem giving the kid a bath, two people taking back to back showers, and running dishwasher at the same time. I think the 80 gallon unit would perform to your liking. I went with the hybrid over an indirect because I have solar that overproduces electric. The hybrid doesn’t use a lot of power on heat pump mode. You could also set your water temp a little higher around 140 degrees and install a mix valve to bring the water back down to 120. That would increase the usable capacity of the heater. Check your utility company for rebates. This is one of the reasons. I chose the hybrid. Im in NY and the electric company gave a $750 rebate for purchasing the hybrid water heater.

ethicalpaul

That is an extremely helpful writeup, @super_snop, thank you.

Mine is just a 1.5 bathroom house and just my wife and I so I upsized as you did, but to a 65 gallon (from a 40 gallon gas unit). I might have considered the 80, but I think I ran out of headspace for it.

My basement is warm in the winter, but it will soon be cooler as I insulate my steam mains, but it will still be next to an 83% efficient steam boiler so even in the winter it should stay reasonable, I look forward to how it does.

I am going for a NJ $750 rebate but I have to work out with the program whether I can install it myself or find a plumber and electrician. NJ lets homeowners do their own work as long as it's permitted and inspected so I'm hoping I can do it.

psb75

Get the right sized tank 50, 60, or 80 gal. from Rheem or Brad/White, for your situation and the air-to-water heat pump water heater will perform reliably. It has multiple settings 1. compressor only, 2. electric induction only, or 3. hybrid which uses both of the aforementioned. Very easy for the user to interface with. Will reduce your hot water costs by 1/3 or more depending on how you use it.

super_snop

@ethicalpaul keep me updated how it works out. Here in NY to receive the rebate all I needed was proof of purchase. I purchased the water heater on black Friday last year and saved $350 plus I got the $750 rebate. All together I got the 80 gallon unit for $1300 including tax. I couldn’t beat the price! I went from a tankless coil off my oil fired boiler to this hybrid water heater and couldnt be happier. Another plus to running it in heat pump mode is that my basement stays very dry. Before I installed this water heater I used to run a dehumidifier year round. Now the heat pump tajes care of it. So I am pretty much making hot water for the cost of what it used to be just to run a dehumidifier.

ethicalpaul

Thanks @psb75, that’s the plan!

@super_snop yes the humidity was a reason for my decision too.

Here in NJ they don’t trust us not to just buy it, take the rebate and then return it LOL so I need proof plus they can do random inspections!

psb75

Keep in mind: these units are not true de-humidifiers. The only do that, when they are making hot water. De-humidification is an unintended "side benefit." In summer you should still run a real de-humidifier in your basement. It will run LESS because of the HPDWH.

ethicalpaul

Yes, thanks for that clarification. I will be watching how it is affected.

Another positive aspect of this is that during all seasons I'll have one less atmospheric burner sucking outside air into the house.

ChrisJ

ethicalpaul said:

Yes, thanks for that clarification. I will be watching how it is affected.

Another positive aspect of this is that during all seasons I'll have one less atmospheric burner sucking outside air into the house.

Interesting fact.
Using recirculating hot water with it will cause it to run slightly more often, and add just a little heat back into the space, causing better dehumidification.

ethicalpaul

Heard loud and clear, @ChrisJ LOL

I got another piece of good news. The NJ WarmAdvantage energy program does allow me to self-install this water heater as long as I get it permitted and inspected, woo!

ethicalpaul

Followup: the Rheem heat pump water heater installed so easy! I have it set to 123F in exclusively heat pump mode. It lets the temp drop a few degrees before bothering to crank up the compressor which is fine.

The 65g capacity over my old 40g NG is perfect. It has a top and bottom thermometer on the status display so you can watch the temp drop first from the top, then from the bottom. The hot water feeds right out the bottom, first time I’ve seen that.

It tells you the ambient temp, the temp of hot water getting produced and some more.

You can set it to use any combination of heat pump and/or resistance.

Attached is a screenshot from the app showing the kwh for every day/week/month. Guess which day she took a bath!

Highly recommended!

psb75

Watch out for that motherboard. I just replaced one today. They don't like power surges (that come with outages). This is the third one for this Rheem HPDW heater. Time, I think for a surge protector.

ethicalpaul

Thanks— a 230v surge protector hard wired into the panel?

Edit: oh, like this: 50 kA Plug-On Neutral Whole House Surge Protective Device

https://www.homedepot.com/p/300716370

psb75

I'm researching for a recommendation and a device. I'll chime in when I find out tomorrow. Good news is: Rheem has been good about supporting their warranty.

psb75

Energy "coach" at my electrical co-op power supplier advises that a "whole house surge protector" be installed rather than a circuit- specific device. A "meter base unit." TESCO 240MSA unit.

SuperTech

For what it's worth we had to replace one board under warranty and had two others leak the refrigerant out of the evaporator coils. Rheem has been good about covering the warranty.
Nice units when they are working, I'm just questioning the reliability and longevity of them. Not my favourite choice for a water heater. Compressors don't seem to hold up in similar models from other brands.

ethicalpaul

> @psb75 said:
> Energy "coach" at my electrical co-op power supplier advises that a "whole house surge protector" be installed rather than a circuit- specific device. A "meter base unit." TESCO 240MSA unit.

Thanks, I’ll look that one up. See also a few messages up where I edited my post to include a whole house type that plugs into the Square-D Homeline panel

JUGHNE

Paul, does your panel have the plug in neutral feature?

ethicalpaul

Yes it does @JUGHNE, brand new install. I have utilized it for one module that has the super-safe anti-spark technology in it whose initials I can't remember

JUGHNE

AFCI.....Arc Fault Circuit Interrupter.

ethicalpaul

That's the one! Anyway, no pigtails here. Why did you ask? To make sure I wasn't looking at one that wouldn't work with my panel? If so, thanks for looking out for me

stretch5881

ethicalpaul said:

Related question: I know water heaters have that insertion tube to put the replacement, cold water into the bottom of the tank while leaving the hot water at the top to be pushed out to the plumbing (provided it's not rusted out--I see they are plastic now)

But even with that, there still must be some mixing of the cold new water with the hot water remaining in the tank, right? How much usable hot water does that remove from the tank's reserve? Does anyone know?

The plastic fill tubes fail also. They get brittle and break off. Mine broke off 4" from the top. I had to fish it out in pieces from the flush hole in the bottom of the tank.

Larry Weingarten

Hi @ethicalpaul , The rule of thumb is that you get roughly 75% of the volume of the tank as undiluted hot water. So, you get 30 gallons from a 40 gallon tank. This is actually only true with uses like filling a tub. A low flow showerhead, because of the time it takes to use those gallons and because of the reduced mixing of hot and cold inside of the tank, will deliver more undiluted hot water. That make sense?

Yours, Larry

ethicalpaul

> @stretch5881 said:
> (Quote)
> The plastic fill tubes fail also. They get brittle and break off. Mine broke off 4" from the top. I had to fish it out in pieces from the flush hole in the bottom of the tank.

Well with these models, the fill port is right at the bottom of the unit, so there isn’t a traditional fill tube.