Heat pumps viable? Vs tank vs tankless

[tknx]

Family of five plus live in nanny. So three adults and three young children. We are in the Oakland area - so low flow shower heads, etc.

Figure everyone takes showers in the morning. Laundry is constant (two front load washers) and we run a dishwasher two to three times a day at times. We are considering adding a steam unit to our shower. So yes. We use a lot of hot water.

I was wondering which way I should go? We are renting right now while we renovate and there is a Noritz NRC-1111 which seems to almost keep up with serial showers but struggle with parallel showers.

We could just do something like two 80 gallon gas tanks plus DWHR and recirculation. This seems like it would be the most efficient.

Or we could try out a heat pump. We are planning on solar. And something like two Stiebel Accelera 300s might work. But my wife is very concerned about the recovery times which can be ten hours or more.

Or a mixed solution? A gas tankless and a heat pump?

 

[Jadnashua]

What are you planning for your HVAC? If you're considering a boiler, an indirect tends to have excellent recovery rates, is very efficient (some have a standby loss of as little as 0.1-degree per hour), and is much simpler and reliable than any of your other choices. Get one with a lifetime warranty, and you should be set. THe kicker is, size it for your worst case use. If I were going to build a new house, I'd want radiant heat, and that generally requires a boiler. So much more comfortable, quiet, and clean.

 

[Sponsor]

 

[smitlab]

It seems very difficult when your family is so crowded, very tight and time consuming. Both them have cons and pros. So it is more useful to ask neighbors and people who has experience

 

[Dana]

Unless you have large tubs to fill an 80 gallon heat pump water heater would likely keep up.

If it's almost all showering use, consider installing a drainwater heat exchanger, which will dramatically increase the "apparent capacity" of an 80 gallon tank. It takes at least 5' of vertical drain downstream of the main shower to return half or more of the heat going drain back to the incoming water stream. The tepid output of the heat exchanger needs to feed both the cold side of the water heater and the cold side of the shower.

The heat exchanger with the lowest pressure drop across it at high flow is the EcoDrain V1000 series, but Renewability's PowerPipe series is also pretty good. The tallest and fattest that actually fits the space is the right one- the installation labor cost is about the same, but the higher heat return of a bigger unit more than pays off in energy savings (and pays off up front if it allows you to use one 80 gallon water heater rather than two.) Expect to spend about a grand for the unit itself- most vendors are Canadian, but will sell direct to US retail buyers. PowerPipes can be purchase through HomeDepot, if that's any more convenient than ordering from Renewability and waiting. (It's not usually cheaper, and may not be quicker to buy through HD.)

If going with gas, an HTP Phoenix with the tank sized for the biggest tub fill with the 199KBTU/hr burner would be a better solution than a tankless + tank. The tanks are all-stainless and should last pretty much forever. A 55 gallon PH199-55 or 80 gallon PH199-80 has a burner as big as any residential tankless, but isn't burner-limited on peak flow the way a tankless is, which solves the parallel shower problem completely.

The burner modulates between 40-199KBTU/hr, and will keep up with a single shower (or maybe even two) 24/365, and would not NEED the drainwater heat exchanger for extra-heavy showering use they way a 55 gallon heat pump water heater would, but it's still "worth it" on both performance and energy use savings perspective if you're doing a lot of showering.

 

[tknx]

I doubt we will do a boiler. If we were doing a complete teardown, I'd consider it since we could run hydronic heat under the floor. But we don't want to deal with radiators and figuring out where to put them everywhere.

So the current plan is:

• HVAC - Carrier Infinity 98 furnace to service two floors (each a zone) + Mitsubishi ducted split for the top floor (want AC for bedrooms)
• I am thinking the HTP PH199-80 is the way to go (or hell, maybe just a 199-119). Add in a DWHR system, and it should be solid.

We will then be taking the condensate water from the furnaces, splits and the water heater and putting it into greywater, so it should be a bit more water efficient.

 

[tknx]

Hmm - It seems like Phoenix PH199-80s are about the same price of just getting two Phoenix Light PH76-80 (or their Westinghouse equivalents).

So is it better to do a single unit for less to deal with and run the burner as needed to get any extra water? Or have more volume but lower BTUs?

 

[Dana]

An 80 gallon tank full of 140F water can fill a 100 gallon Jacuzzi at N.Cal type incoming water temps. Why do you think you're going to run out? Do you have three big tubs that might all need filling at the same time?

It's possible that a SINGLE 80 gallon Light Duty with the 76K burner can cover all your loads. That's about twice the burner of a typical 50 gallon standalone, and substantially more storage capacity too. I was throwing out the big-burner Phoenix option as an example of something that would beat most 80 gallon tank + tankless options.

It's also possible that an 80 gallon heat pump water heater would cover it too, but the recovery times are a LOT slower than a 76KBTU gas-burner.

Water use by laundry & dishwashing is miniscule unless you're running a professional service and running a handful of washers at the same time. If it's just one washer, even if it's in constant use, it's just a blip of intermittent not very big draws. At 50F incoming water and a 140F storage temp the US-average 8 minute 2 gpm shower is only going to draw 9.6 gallons out of a 140F tank. Six of them back to back in succession or in parallel only add up to 58 gallons, so it'll make it. You'd only need more than 80 gallons if you're filling more than two standard sized bathtubs at the same time as some other large load, such as shower.

Which Mitsubishi had you been looking at for the second floor? Their smallest bigger deal split air handlers may be bigger than the upstairs cooling load, and some of them only have a ~2:1 turn down ratio, which isn't enough room to modulate down to your actual loads. To get max comfort & efficiency out of modulating systems it's really important to get aggressive accurate Manual-J load numbers before selecting the equipment.

The HVAC plan in general sounds like overkill. The smallest Carrier Infinity 98 is 60,000 BTU/hr (max-in) and even locked to run at it's minimum output of ~24,000 BTU/hr would be somewhat oversized for a code-min 2500' house in Oakland. At full fire it's ludicrously oversized (which is true of all too many hot air heating systems in the US.) Being ludicrously oversized doesn't hurt hot-air system efficiency, but it takes a real toll on comfort. When it's actually cold out you want the thing to run nearly continuously modulating with load almost never satisfying the thermostat rather than suffering the chill in the pauses between burns. Set up to run 2 zones it'll satisfy any single zone pretty quickly due to it's oversizing, with lots of down time between calls for heat.

You can do better!

Even a sub-code ~1200' ranch house in Sacramento can be heated & cooled by a 1-ton or 1.5 ton Fujitsu slim-duct cassette mini-split. A first floor of a 3000' 2-story might be fully covered for both heating & cooling with the 3/4 tonner. (Oakland's 99% design temp is 36F, 4F warmer than Sacramento's 32F, so your heating loads will be somewhat lower, all else being equal.) Have you had any careful load calculations done? (Don't trust the average HVAC company to do it right. A RESNET rater, engineer, or architect selling load calculations as a service is a better bet.)

The 1.5 tonner in the pictures is the installation in the house in the blog link. With 21,600 BTU/hr nominal capacity @ +17F (over 25K max) it's a bit overkill for the 99% load at 32F, but not ridiculously overkill like an Infinity 98 almost certainly is for your house Unlike the Infinity 98 it can modulate down to as low as 3100 BTU/hr out @ 47F. That's barely 13% of the min-fire output of the smallest Infinity 98, which means it will always run extremely long, comfortable cycles, even when it's not super-cold out, modulating up /down a bit to stay near the setpoint without actually turning off or blasting at full-power.

If you program the wired remote to behave like a thermostat (sensing temp at the remote rather than it's modulating based on the temperature of the return air) it can deliver ultra-stable temperatures at VERY high as-used efficiency in your climate, and would probably even have a cheaper operating cost than a gas-burner.

That ~15" deep ~40" wide closet is the extent of the "mechanical room" for the heat pump! The big grille is the return. There's a very short wide plenum before it splits out into four flex runs to remote registers, some of the ducts are boxed in by soffits below the ceiling level. If you have a full basement the first floor system and ducts could all be in the basement. For the second floor something like this installation could work, or putting it in the top/side of a closet, etc.

A mini-ducted Fujitsu (size TBD by load calculations) per floor would really do it for most houses in your area, unless it's huge sprawling ranch or something. The guy who designed and implemented the system in the pictures is Larry Waters, who posted in the picures in the comments section. He seems very competent, and he posted his number in the comments section too: 707-342-1981

 

[tknx]

Dana - thanks for your input.

HVAC
HVAC in the Bay area is a hell of mediocrity and crap. I interviewed 15 contractors to find one that will do a room-by-room Manual J and D. So we shall see what they come back with. I have been desperately trying to find someone who doesn't do massive oversizing.

House size is 4170 with about 1000 on the bottom floor and 1500 for each of the other two. The master bedroom is getting its own zone as it is quite large and has west facing windows that are single pane and have zero heat rejection. The rest of the house stays quite cool. Access to the top floor for ductwork is very, very limited. There is almost no way to get the ductwork up and a decent return down.

So there are a couple of things going on. I have very little faith in any of the HVAC contractors. So picking an oversize unit is going to happen. I might as well upgrade to one that has a high level of variable speed to avoid short cycling.

For the top floor, the master bedroom is really its own zone. We'd also like airconditioning. So we could use a heat pump, but it would require significant roof penetration and would still be difficult to fit. The Mitsubishi ducted air handlers could sit in the attic and two of them just for zoning. Which is less than ideal.

I will definitely call Larry

Plumbing
Most likely we will go with one HTP Phoenix Light 80 gallon + DWHR. Figuring at worst case if we feel it isn't sufficient, we can add another (space is not an issue).

 

[Dana]

BTW: That house in the GTM blog is is in Berkeley, not Sacramento ( I think Larry Waters had separately mentioned a similar house in Sacramento heated with a 1-ton Fujitsu, or maybe I hallucinated the whole thing. )

The heat gain (and loss) on the west facing windows can be cost-effectively reduced with low-E storm exterior windows, at a fraction of the cost of replacement windows. The bottom of the line Larson storm windows sold through box stores are only so-so, but you can order the better grade versions which are substantially more air-tight, with better latch & slide hardware. The low-E glass costs more, but it pays back quicker in heating bills, and lowers the solar heat gain coefficient from about 0.60 for a clear glass single pane to about 0.45. That's a 25% reduction in heat gain and will lower the air conditioning peak. But it also improves the U-factor from about U0.9 to about U0.35, about a 60% reduction in heat loss at the windows. Here's a deeper dive on the topic, if you're curious.

With a mini-duct cassette there's no need to run ducts between floors. The ducts and cassettes will pretty much stay at/near the floor they're serving.

The amount of roof/wall/floor penetration for refrigerant lines etc for a heat pump aren't any different than those for split AC. They are essentially the same thing, the difference being a heat pump has additional valving and controls within the unit to reverse the flow from cooling to heating.

Any Mitsubishi 0r Fujitsu multi-split serving two mini-duct cassettes is already a heat pump, but multi-splits aren't fully modulating the way the individual mini-split units are. The MXZ-2C20NAHZ or (older, but still made) MXZ-2B20NA have about the same max capacity as the 1.5 ton Fujitsu single mini-duct, but more than twice the minimum output. So when just one of the zones is calling for heat/cool it's quite a bit more air, but still about the same output as a 3/4 ton window-shaker at minimum compressor speed. They're not as efficient as the singles, but you can serve more individual zones without a wall or hard filled with compressors. Single zone mini-split efficiency when modulating at part load SOARS, and can beat their AHRI rated HSPF and SEER numbers, if sized properly to the loads. Multi-splits don't have that advantage.

I wish I could say that the Bay Area is unique as "...a hell of mediocrity and crap...", but that seems to be the long standing state of the industry. There are real pros out there, and another layer of well intentioned if somewhat ignorant willing to accept some direction, then there's the other 95%. The most recent HVAC up grades at my house was of the well-intentioned type contractor who wasn't comfortable unless I signed up for taking responsibility for the design actually working or not (which I readily did.) One of the designers working for that contractor bet the owner $100 that it wasn't going to cut it and that I'd be left in the cold with the equipment I specified, but lost that bet. (A decade later having seen outdoor temps 20F colder than the design temp I'm still not freezing. )

 

[tknx]

I spoke to Larry and he seems like the right type of contractor - they said they usually don't deal with my suburb (Piedmont) but he is trying to get an exception made.

The windows are three huge round top affairs. And if we replace them, we will cut the rest of the way down to the floor and make them french balcony doors. So we will probably just have them covered with film for now and save that for a Phase II project.

I am still trying to figure out a strategy for using a regular heat pump on the top floor. Maybe it would have to be roof mounted, but that would probably be a better solution. Plus giving us zoning flexibility since the bedrooms are all a bit different.

 

[Jadnashua]

Radiant IN-floor heating really doesn't matter about furniture placement. But, yes, radiators or convectors can. It's not the cheapest to install, but it is the most comfortable way to do it.

 

[tknx]

Thanks everyone - this has been hugely helpful.

The Ecodrain is bookmarked and noted!

What about recirc? Constant flow? Or on timer? Which unit would be best for a large three story home? I see Grundfos and Laing mentioned. Occasionally Watt.

 

[Reach4]

What about recirc? Constant flow? Or on timer? Which unit would be best for a large three story home?

Best for what? Energy savings, convenience, what. Continuous is convenient. Best energy savings would be a switch that turns on the recirculation pump for a timed interval. That involves a wait time, but no energy use unless you intend to use hot water. For a system like that, you would pump at a higher rate than you would with a timed or continuous with thermostat, to minimize the wait time.

I don't have system recommendations, but I just wanted to point out another possibility.

 

[Jadnashua]

I have a unit from RedyTemp. Going on 13-years now, still works as new. Has not needed any maintenance. It can be integrated with an aftermarket timer...I've had to replace a few of those, but that's not the unit's problem. I think I'm on my third one, but they're cheap.

If you have things all open, insulate all of the hot water lines and run a dedicated return line(s). Depending on the plumbing layout, you may need more than one pump, or potentially, multiple temperature controlled valves to ensure the water gets pumped everywhere it's needed. A small pump with thermally controlled valves that close once the water is hot where needed means that it doesn't constantly circulate. The insulated pipes keep things warm longer, then, when it cools enough, the valve reopens, bringing it back to design temp. Those valves are generally set so you have warm water there immediately, but hot isn't far away. Good for say washing your hands, but the higher volume of say a tub or shower, still starts out warm, but quickly gets hot because of the higher volume. In my case, the pump is located at the furthest point, so it pulls hot water by all of the other things in the house so my shower gets hot almost instantly since it's closer to the WH.

 

[tknx]

We will have four stories to cover for water heater to top floor.

Ideally the pump would be a bit of both - start at around 5:30am, stop at 8:30am. Then around 4pm check and maintain the temp til 8pm. That would cover our usage periods.

 

[Jadnashua]

It's not so much the height, it's how the plumbing is arranged. In a closed, pressurized loop that is full of water, the falling water helps to pull it up, aided by the pump...but, water will take the path of least resistance, so unless you have one main, and short branches off of it, a single return may not get the hot water to flow close enough to every fixture you want hot.

There are a couple of different ways to do this efficiently. You don't really need maximum WH temp water in the entire line as that will maximize the heat loss, but you do want it close. If your main line branches a long ways to get to things, unless you add a return line at the end of each long branch, your performance may not be great...it will still be better than trying to drain the entire line back to the WH though.

Many of the systems use a mechanical, bi-metallic, thermostatically controlled valve to stop the flow once the line is hot. You'd need one of those on each longer branch, so may need multiple return lines (they could be combined at some point, but you may need check valves as well). You can use aquastats, and shut the pump off, but doing that for multiple branches may end up being a pain, and wiring it all up could be a pain.

In my case, with the RedyTemp unit, it is entirely self-contained...the pump, cross-over (or return if you have a dedicated return line, mine doesn't, it uses the cold line) and check valve is in one fairly small box. I have it under the vanity furthest away from the WH. But, the way my place is plumbed, all of the other outlets are short branches off of that line feeding the vanity at the end, so one valve/cross-over works for me. It may not for you. Most of those valves are set to stop the flow at a water temp of around 105-degrees. The RedyTemp unit has an adjustable aquastat in it. I have mine set to get it just warm, but since everything else is closer to the WH, it's hotter there. This also limits how much hot water gets pushed into the cold line (not a problem if you have a dedicated return). In my situation, flushing the toilet in that bathroom clears all of the hot out of the cold line except for maybe about a foot or so, which clears in maybe a second.

 

[tknx]

Okay. Sounds like this is a question for the on site plumber.

Thanks. That was super helpful and made a lot of sense.

 

[Dana]

I spoke to Larry and he seems like the right type of contractor - they said they usually don't deal with my suburb (Piedmont) but he is trying to get an exception made.

The windows are three huge round top affairs. And if we replace them, we will cut the rest of the way down to the floor and make them french balcony doors. So we will probably just have them covered with film for now and save that for a Phase II project.

I am still trying to figure out a strategy for using a regular heat pump on the top floor. Maybe it would have to be roof mounted, but that would probably be a better solution. Plus giving us zoning flexibility since the bedrooms are all a bit different.

Custom fixed (non-operable) exterior low-E storm windows are commonly used in my area to improve the energy performance of historical buildings, and may be "worth it" here.

How is a "regular" heat pump different from a ducted (or ductless) mini-split? Most standard split systems are going to be way oversized for the cooling and heating loads of a single floor (even a top floor with expansive window area.) I'm sure Larry Waters will be able help you sort out appropriate options. Idiots who use ridiculous rule of thumb such as "A ton per 500'" or "...ton per 750" would say you need 2-3 ton for a 1500' floor. Even in hotter more humid locations than Piedmont such as the gulf coast states end up with tonnage/conditioned space ratios of a ton per 1500' or so. Allison Bailes (a by-the-Manual-J contractor in the Atlanta GA area) plotted square feet per ton against house size for a few dozen projects his company ran the real numbers on (most of them in the southeastern US, with a few outlier from other regions.):

A barely-insulated upper floor with a lot of west facing glass with window film in Piedmont might be in the ton per 1000 range, but it could also be more than 1500', which is why it's important to run the real numbers.

 

[tknx]

Yeah - this is why I have been so miserable finding a contractor. One HVAC contractor I spoke to (who only does repairs now), told me he thinks the Bay area has the worst HVAC contractors in the country because it is generally temperate here. I believe him.

Just two examples:

1. One guy came in and said they would absolutely not do a room-by-room Manual J nor Manual D, even if I was willing to pay for them. He said all diffusers are the same and do I want a 2-way or a 3-way. That guy was out right away.
2. Another didn't know what a Manual J was.

So the two finalists I have (Larry and one other company) will do it. I am waiting to see Larry and he is my top pick based on our conversation, but apparently they hate working in Piedmont because of noise.

I am going to go and measure out each window this week as some kind folks online were willing to help me do a Manual J to get a good sense of what is needed.

As for the windows - they are very large round top windows and pretty - so expensive to replace. There are three of them. If we replace them, it will definitely be with low-E windows. Actually we would run them to the ground and make them french balcony doors. That may be a "Phase II" project. For now, we will probably cover them with film.

 

[Dana]

Low-E storms are a LOT cheaper than a replacement window, and when installed on the exterior side of pre-existing single pane brings the net performance up to roughly that of a code-min replacement window.

A low-E storm window is just a single-pane window in a light frame, with a pyrolytic hard-coat (hard to scratch) low-E coating on the interior facing side of the glass. They are designed to be sealed & screwed to the existing window's structural frame. That's a lot cheaper to make than a sealed-glass gas-filled double-pane, especially sealed glass that has curves.

If you want to take a shot at your own Manual-J using freebie online tools, loadcalc is easy to use. If you use the most aggressive assumptions for air tightness, R-values, and shading factors won't lead to ridiculous oversizing. It tends to overshoot by a bit, but usually not by more than 25-30% compared to the output of more serious Manual-J tool. Be aggressive but reasonable for R-values, eg: don't use R20 for wall insulation a 2x4 framed house, etc. but if there's anything at all in the walls, use R13 for milled 2x4s (3.5" deep), R15 if it's high density fiberglass or full dimension 2x4s (especially if balloon framed.)