DHW: Gas vs "Hybrid"

ethicalpaul

Existing situation: 2 person household with an old 40 gallon NG water heater in open unfinished basement next to steam boiler.

It would normally be plenty of hot water but I installed a 70 gallon soaking tub for my wife and she runs out of hot water when it is just about full.

I wanted to replace the old heater anyway and I am torn between a nice modern gas unit of 50-65 gallons and a 65 gallon Rheem "hybrid" (heat pump) model that I would want to run almost always on Econ mode (heat pump only, no coils used). I'm not worried about concurrent use with the tub...we just don't use very much hot water generally.

I'd love to get rid of a fuel burning appliance, especially for one that costs less to operate. I wouldn't mind the slight cooling effect in the summer, and in the winter the space is plenty warm from the boiler so I think I'd be fine there.

I guess it's just up to recovery time vs my philosophical preference for moving heat rather than burning stuff to make heat vs the reliability of this new (but not really new) tech. I have no idea why the early hybrid models were such junk, it's not new science, but I guess they really were junk. Has Rheem finally got something that will run?

Thanks for any opinions, I'll take them all

ethicalpaul

PS: Indirect DHW off the steam boiler is the only option I'm opposed to...I can't imagine keeping a 75k btu steam boiler at 80% efficiency stoked for 6 months blasting heat into the basement just to be able to pull some heat from it for water.

Zman

Slowing down the tub fill rate is an easy solution.

Zman

Your existing heater is producing ~32k/btu. The hybrid will be ~16k/btu in inefficient mode.

Intplm.

The hybrids are not for everyone but your situation sounds like it will work for you. If you are looking to fill a 75 gal tub. (Wow thats a lot of tub.) I would purchase the largest unit that you can afford, and that- -will fit- - in the basement.
The thought of having it on "Econ" mode is fine but I think you will have more success when you have the heater on "Hybrid" mode. Even if the unit will be installed close to the boiler it may not supply enough heat to the water in Econ mode. The surrounding heat may not be enough.
What's good about this is you are someone who does there home work and will make mode adjustments as needed. These hybrid water heaters do offer some nice choices as to how you can heat the water.

If you decide on a tankless water heater look into a Rinnai 98 or equivalent. More of a expense but will supply hot water without running out.
I own a Rinnai 98 series (I do not have brand loyalty) . Look into Rinnai or a equivalent brand.
My unit supplies hot water without any noticeable temperature swings.
If you have city water and natural gas these units like that combination, as opposed to a private well that can have pressure swings and hard water that can hinder performance.

Jamie Hall

It will work... if you slow down the fill rate to accommodate the leisurely recovery of the hybrid.

And if the hybrid continues to work. There are two in buildings which I maintain. Both have failed (compressor problems) within two years of installation. $$ labour to replace, even under warranty. Oil is going in one of the buildings (already has oil heat) and LP gas in the other (already has LP heat).

ethicalpaul

Hmm, regarding fill rate, my goal was to size the tank to not have to slow the fill rate. It’s 70 gallons minus about 20 gallons for the occupant, times about 3/4 for the temperature mixing at the faucet.

Jeez Jamie, the units are STILL not reliable?? This is depressing

I don’t think I can do tankless because the fill rate is slooooww, right?

ethicalpaul

Zman said:

Slowing down the tub fill rate is an easy solution.

You haven't met my wife

Here's the tub by the way, nothing extravagant but yeah, 70 gallons (but I think that's without an occupant if you fill it to overlow): https://www.homedepot.com/p/American-Standard-EverClean-60-in-x-32-in-Left-Drain-Soaking-Tub-in-White-2425L-202-020/203160966

ethicalpaul

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?

ethicalpaul

Intplm. said:

If you have city water and natural gas these units like that combination, as opposed to a private well that can have pressure swings and hard water that can hinder performance.

Interesting point there. I have city water, but it's never higher than 40psi (which I am annoyed by) and there are several times a month where I'll be using the water and the pressure will go down to 0 (full stop of flow) and it will even pull air into the pipes. Then it will come back within a few seconds, as if there was a transfer of pumping stations or something???

I've tried calling the municipality's water department about this but they don't return my calls.

JUGHNE

If I tried to slow the flow into my wife's tub, I would be in trouble as the water would cool off to much. At least the same water capacity as yours, maybe more.
Then as the Lobster cooking goes on and the water cools off more it is constantly being topped off to keep the temp up.
I would have to wait 30 minutes before I could get in.
We have a 120 gallon tank, separate heat exchanger and 80,000 ModCon which keeps up OK.


On This Old House they showed a separate compressor unit with water lines piped into any existing tank. I thought this was a good idea as either the tank will leak or the compressor goes out. Changeable components in that case.
However, I have never seen that set up again anywhere.

ethicalpaul

Yes @JUGHNE that is exactly my situation. She would like to fill it with nice hot water (say 50 gallons) and then still have some left over for warming, or for washing her hair with the hand sprayer. Currently it fills decently warm but then she's out of hot water.

It sounds like I just get a big tank regardless and then decide if I want to roll the dice on the hi-tech.

For the pressure issue I too thought about looking into a pressure tank with a pump but haven't gotten too serious about that research.

EBEBRATT-Ed

I have thought about a hybrid myself. My problem is in the condo I have a very small basement. Not sure I would get the heat transfer for the evaporator the cellar would get pretty cold. And can't have outside condensers here.

Also with the problems @Jamie Hall had I am going to wait.

This is my take. I can service the refrigeration end myself so that wouldn't be an issue.

If I couldn't service it myself I wouldn't put one in. But, that's just me. No gas here, all electric

JUGHNE

In our little town we have 40PSI water pressure.
Some years ago the pressure would drop like yours and depending how close you were to the pump, you might suck air.
Our problem was a slow closing check valve on that well....the water would run back down the well.

That has been corrected now.

In this state if a muni water supply loses pressure and there is even a chance of sucking air then the system must be water tested and have about a week of chlorination.
The State health dept is very concerned about this.

If you E-mailed your water dept with the same concern, (not quite threating to contact the state) it may get their attention.

Zman

If you throttle the fill and blame it on low water pressure would she figure it out?
I have a tub like that with a high flow valve. A 60 gallon indirect with 135,000 boiler behind it keeps up, barely....

ethicalpaul

Thank you @JUGHNE I would think any reasonable water entity would be very concerned about negative pressure. I will try to gently poke the bear.

@EBEBRATT-Ed I too was aware of the the fickleness of these units, but that was some years ago and I was hoping that they had settled down. I might still give it a shot because it's my nature to push things a little

Intplm.

I would talk with a company rep. about your situation before installing a tankless. Your water flow problem could be the deciding factor.
You might just have to go with the hybrid. Take some measurements to be sure a hybrid will fit in your basement. The larger models can be very tall.

Intplm.

@ethicalpaul is that tub pictured above installed ? If not, there is a company called "MTI bath" that offers a tub with a integral heater. It would supplement the water heaters output.

SuperJ

How hot is your tank? If it's at 140F with a thermostatic valve, it's virtual capacity exists it's actual capacity by a pretty good margin since no one can bath in 140F water.

Personally I might go electric the next time around with the lower element replaced by a home brew DC element powered off a solar panel or two.

ethicalpaul

> @Intplm. said:
> I would talk with a company rep. about your situation before installing a tankless. Your water flow problem could be the deciding factor.
> You might just have to go with the hybrid. Take some measurements to be sure a hybrid will fit in your basement. The larger models can be very tall.

Yes, thanks. Tankless has not been on my radar due to the flow rate. I’ll definitely measure twice 😉

And yes, it’s installed. I didn’t really want to run 220 to my bathroom or even have 110 touching my bathtub

ethicalpaul

> @SuperJ said:
> How hot is your tank? If it's at 140F with a thermostatic valve, it's virtual capacity exists it's actual capacity by a pretty good margin since no one can bath in 140F water.
>
> Personally I might go electric the next time around with the lower element replaced by a home brew DC element powered off a solar panel or two.


Well now that’s really pushing the envelope! At my last house I put in a solar loop with a preheat buffer tank, it was OK and would have paid for itself in 57 years or so 😅

I have to measure the tank I guess...it’s set at “very hot” but it doesn’t seem that hot. I’m counting on that mixing percentage yeah

Intplm.

ethicalpaul said:

> @Intplm. said:

> I would talk with a company rep. about your situation before installing a tankless. Your water flow problem could be the deciding factor.

> You might just have to go with the hybrid. Take some measurements to be sure a hybrid will fit in your basement. The larger models can be very tall.



Yes, thanks. Tankless has not been on my radar due to the flow rate. I’ll definitely measure twice 😉



And yes, it’s installed. I didn’t really want to run 220 to my bathroom or even have 110 touching my bathtub

220 or 110 is not near the tub. MTI Bath has a low voltage heater that works great. I have one in my own home. No voltage issues. No danger . Worth looking into if not now than in the future. Saves you a lot of trouble when the 50 gallons tub water starts to cool. The heater helps to keep the water warm longer. FYI.

ethicalpaul

Thanks @Intplm., I probably should have looked at a tub heater.

But it looks like the winner will be: https://www.homedepot.com/p/Rheem-Performance-Platinum-65-gal-10-Year-Hybrid-High-Efficiency-Smart-Tank-Electric-Water-Heater-XE65T10HD50U1/303419586

Larry Weingarten

Hello, I've got a few thoughts. First is how often will the tub be used? Most households use their tub 3-4 times per year. Can I assume you will use it a lot more than that? Next is what's your groundwater temperature? Knowing that would help in sizing the tank. As a rule, you get 70-75% of the volume of the tank as undiluted hot water. So, pessimistically, that would give you 45.5 gallons from a 65 gallon heater. A person might displace 10-15 gallons in a tub. So, you would need up to 60 gallons for tub filling. Given all that, I'd be more comfortable installing an 80 gallon unit. The problem becomes odor in the water because water sits too long in the glass lined tank. This is where frequency of tub filling comes into play. If you take a tub bath often, no odor problem. Otherwise, you might be better off using the smaller tank and topping it up with resistance heating before filling the tub.

Yours, Larry

ethicalpaul

I would say once a week for this tub. I'd like to install the 80 gallon, but I think that one is too tall, but I'll measure to make sure. What you say makes sense.

I appreciate your 70-75 percent of undiluted water figure (I too think that as cold water comes into the tank it must mix with the hot that's in there), but that must be about offset by the mixing at the valve of the hot water I would think so I hope to get 60 gallons of bath temperature water out of a full 65 gallon tank. I'll let you know!

Larry Weingarten

Hi, You can make the 65 gallon tank work, but you may wind up needing to turn the temperature up higher about an hour before tub filling and putting it in electric resistance mode. Higher temp storage will be harder for the heat pump to add energy to. Studies have shown that bigger storage increases COP of the heat pump, so from that perspective, more storage would be nice an increase the likelihood that you could simply leave it in heat pump only mode. The math isn't hard for using desired temp, (say 105F) and hot water temp, (say 140F) to determine what your mix of hot and cold is; once cold temp is known. One more thing, have a look here http://www.dsireusa.org/ to see if there are any incentives available to you for putting in the HP.

Yours, Larry

EBEBRATT-Ed

Just wondering and throwing this out their for all refrigeration types.

Seems to me for a heat pump water heater to heat water in the 120-140 degree range is probably forcing the compressor out of it's comfort range and shortening it's life. And to get that temperature the evaporator has to run at least 10 degrees warmer than that.

So my question is can anyone name an air conditioning or refrigeration system where the condensing or (evaporating side with HP) operates at 120-140 degrees (130-150 evaporating temperature)

Maybe Phoenix, but even that isn't year round.

Larry Weingarten

Hi, Maybe something like the Sanden CO heat pump? https://www.sandenwaterheater.com/

Yours, Larry

Intplm.

@ethicalpaul I think what you have decided is fine. Run the water heater at 130 deg. F should do all that you want.

Zman

Have you considered upgrading your existing gas heater? You can get 2 or 3 times the output of a hybrid and likely a lower energy cost. Your application sounds like it is the opposite of what hybrids are good for.

ethicalpaul

Yes, a modern gas unit was the other contender. See the title of the thread 😀

Why is it the opposite of a hybrid’s strength?

hot_rod

Here is a product that might fit your needs

http://www.htproducts.com/RGH75100.html

Jamie Hall

ethicalpaul said:

Yes, a modern gas unit was the other contender. See the title of the thread 😀



Why is it the opposite of a hybrid’s strength?

A hybrid is intended to -- and does, very well (assuming it's working) to steadily heat water to some temperature -- typically around 120. It stores that in a tank, which is used to meet peak demand situations -- by which, in the case of a hybrid -- a low flow shower head or two. If it is ideally matched to the usage, it will run almost continuously, 24/7. Recovery, however, is slow -- which is why they all have electric resistance heating elements ($$$!) to handle situations where shower 1 runs you out of hot water and shower 2 is annoyed.

Gas -- or oil -- on the other hand, is intended to heat and store some hot water -- say 40 to 60 gallons -- but to handle longer demands by firing up and recovering. A good gas or oil water heater -- as it might be the three in the buildings I maintain -- can handle 2.5 gallons per minute all day... Which, combined with the storage, can meet some pretty hefty demands.

Such as your hot tub...

ethicalpaul

It’s just a bathtub, but yes.

But with me sizing it to handle our biggest need and so little other use, I was thinking it’d be OK. I can force it to not use the coils...the tub would be in the evening with all night to recover slowly.

But I’ll keep thinking. I have to upgrade my electric panel first anyway

Intplm.

What does that hybrid require for wiring? #10 AWG with a thirty amp. breaker?

ethicalpaul

Yes exactly. I have the amps but I can’t find breakers in my old tan-switch cutler hammer

EBEBRATT-Ed

@ethicalpaul

Cutler hammer breakers are still available as far as I know. Look for a wholesaler in you area that sells Eaton.

Tim Potter

your 1700 HD hybrid only has a first-hour rating of 75 gal, can your wife wait an hour to jump in the tub? HR's suggestion has a first-hour rating of 107 or 130 depending on the btus. even with the 100,000 btu model its still about a 1/2 hour fill....

Tim

ethicalpaul

I don’t think she’ll have to wait an hour. The tub is 70 gallons but she is like 15 gallons and the tank will be full of hot water at time 0.

Even the crusty 40 gallon we have now fills the tub but just barely

Intplm.

ethicalpaul said:

Yes exactly. I have the amps but I can’t find breakers in my old tan-switch cutler hammer

A electrician may no better but I believe GE breakers fit nicely in a cutler hammer breaker panel. They used the same design.
You can also install mini breakers if you need to make space to accommodate the 30 amp breaker in your panel.

ethicalpaul

Yeah, it’s now Eaton, but my panel uses these ones with a cutout in the back that I can’t find. And trust me, it needs to be swapped out