Heat pump water heater not quite warm enough in winter

[Tomject]

We've got a 100+ year old house in Portland Oregon, it has a 50G hybrid heat pump water heater in the unfinished but warm basement. We have 2-4 people living here. During winter months we've found it often doesn't get warm enough water to the 2nd floor shower. In the summer, there are times when full hot is too much for me. But in winter, I turn it all the way up, and it's not that hot. I don't think it's even 110F today.

In the winter, the inlet temp is quite a bit lower than summer, but you'd think with a tank (not on-demand) heater this shouldn't matter so much. The house has varied amounts of insulation, so it's possible that where the hot supply runs to the shower the pipe is just loosing too much heat. During a recent kitchen remodel, I was able to re-route some of the hot 2nd floor supply to give it 10 less feet of exterior wall exposure, but there is still some where I didn't have access. That did seem to improve things slightly.

I tried adjusting the shower mix valve- thinking there was some sort of anti-scald device. No change.
I turned off the cold supply to the shower mixing valve just to be sure- again no change.
I tried turning the hot water heater all the way up 140F, and it's slightly better, but still not adequately hot for all of our needs.

Is it possible the heat pump side of the water heater works in some sort of on-demand mode where it's not able to put enough heat into the water during cold months?

Ideas we've floated for improving situation:
Tear into walls/floor and rerouting hot supply to all interior walls (if that's even possible)
Adding an on-demand unit near the shower, but would need to run a lot of electricity up there, also difficult.
Add some sort of additional room heater to the bathroom to lessen the feeling of a cold shower in winter time.
Run the heater in non-heat pump mode to see if that helps.
Test water temp at various locations to see if we are just becoming wimpy in our old age.

Any advice from this amazing community of experts would be welcome.

 

[Fitter30]

Measure water temp at the heater then the shower. Might need to use the elements to raise the temp.

 

[Sponsor]

 

[John Gayewski]

I'm not to familiar with different models of these, but I always thought the heat pump was primary heating source, but after a certain amount of time below the set temp them it should kick on the electric heating elements. Which have more power and are there for your exact situation.

 

[Fitter30]

Have u talked with insulation contractor to see what's available without taking out a wall. Explore sites for houses like yours.

 

[Tomject]

Have u talked with insulation contractor to see what's available without taking out a wall. Explore sites for houses like yours.

I know we can have more insulation blown into the wall cavity, but the the pipe is on the exterior side of the wall, I would imagine that it would only make things worse, as it would block heat from reaching the pipe.

 

[Tomject]

I'm not to familiar with different models of these, but I always thought the heat pump was primary heating source, but after a certain amount of time below the set temp them it should kick on the electric heating elements. Which have more power and are there for your exact situation.

This unit has an option to run in heat pump mode, hybrid mode, or electric heat only. I'll have to try it in electric only mode to see if that helps.

Measure water temp at the heater then the shower. Might need to use the elements to raise the temp.

I'll do this first. If the temp at the heater (or close to it) is closer to the setpoint (140F) when the shower is not warm enough then it's an insulation issue? And if both are adequately hot, then it's the heater not making enough hot water when we need it?

 

[wwhitney]

I know we can have more insulation blown into the wall cavity, but the the pipe is on the exterior side of the wall, I would imagine that it would only make things worse, as it would block heat from reaching the pipe.

Once you confirm that the temperature at the tank is as intended (e.g. 130F), then if the temperature at the fixture is too low, you know the problem is heat loss along the pipe in the wall. I.e. the problem has nothing to do with your water heater.

Then all your options probably involve opening walls. You could reroute the pipe through interior walls, and there's a small chance that may be possible with minimal disruption by fishing through finished walls. Or you can open up the exterior wall with the pipe (from the inside or outside, depending) and add insulation between the pipe and the exterior, and air seal the cavity better.

Cheers, Wayne

 

[Fitter30]

Guess im confused pipes are exposed on a exterior wall?

 

[wwhitney]

Guess im confused pipes are exposed on a exterior wall?

As I understand, the pipes between the water heater and the problematic shower are known to run through uninsulated (and likely poorly air sealed) exterior walls. So the problem is likely just heat loss within the wall cavity, as the wall cavity temperature is likely closer to outdoor temperature than indoor.

Cheers, Wayne

 

[GrumpyPlumber]

Portland Oregon + water pipes in outside wall = bad news.

I'm in roughly the same latitude, water temperature is the least of the problem, freezing is the biggy.

.

 

[Reach4]

Portland Oregon + water pipes in outside wall = bad news.

I'm in roughly the same latitude, water temperature is the least of the problem, freezing is the biggy.

Latitude is not the whole story. You will see the frost line gets more shallow near the Pacific.

https://www.hammerpedia.com/oregon-frost-line/
https://www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs/images/figure13.gif
That second map is in meters.

 

[Fitter30]

Hot flows to cold. Insulation slows that transfer down. Any exposed hw piping and fittings should be insulated.
Bare copper 3/4 loses 45 btu/ hr per ft @68° differance.

 

[Jadnashua]

A typical pressure balanced shower valve will have a stop that limits how hot it can get. It may be just simply adjusting that limit so the shower can get hotter. At a sink or other outlet that has a single handle outlet, run it full hot and see what temperature you get. My guess is that it will be more than enough. The default setting of a typical valve is set with a fairly common cold inlet, and the winter inlet is much lower, so you'll need more hot to make it comfortable.

 

[Tomject]

Well! some updates for ya'll, and continued thanks for your help...

This morning after taking another not very hot shower (and reinforcing that it's not my girlfriend who is bothered by the lack of a truly hot shower) I measured shower temp at 106F. Basement sink near waterheater was 133F. With a sinking feeling of impending wall/floor renovations, I remembered to measure the bathroom faucet, and it's 130F. Ok, I know the shower hot water pipe runs inside the exterior wall for a bit before it gets to the shower, but there is no effing way that 6' of PEX is loosing 25 degrees of heat when it's 39F outside. And BTW, so far we've not had any frozen pipes through the past winter when it was 20F for a week.

I could have sworn that I'd adjusted or removed the anti-scald ring inside the shower mixing valve, and also had tested water temp with cold side off, but figured I should re-check, since things just in case, and because this problem isn't making sense.

In the photo below, I tested various settings of turning A and B off, and they unsurprisingly controlled hot and cold supply to mixing valve. Then I had a look and D and C, and realized I could simply remove C, which was limiting the maximum temp... and voila! Suddenly the shower is back to 130F! I adjusted D as a stop for the 'off' setting, and put it all back together.

Is it ok to just remove part D, and turn the water heater back to a more reasonable setting now?
Added bonus, I can stop melting plastic take-out containers in the dishwasher...

 

[John Gayewski]

I wanted to say it was impossible to lose that much heat on the way to the shower after the thread started to drift on that direction, but crazy things can happen.

Glad it's the same reason everyone else complains about cold winter showers. The aniscald limit thingies are about ridiculous. We always turn them to their highest settings as these are a call back item. I wish I would have thought about suggesting this as it's so obvious.

Sometimes the description is better left very simple as it's easy to steer people in the wrong direction by suggesting things that are less likley. I need to be better at identifying these things.

 

[Tomject]

When we first moved in, that was the first thing I tried when we discovered the not-hot shower situation. Confusingly there was a second plastic ring on the handle that I thought was the anti-scald, and when that didn't work, I could have sworn I tested turning off the cold supply to mixing valve to prove the valve wasn't the issue. Apparently my brain is turning to the same mush that is no longer hodling together the cracked areas of plaster in my walls.

 

[WorthFlorida]

When we first moved in, that was the first thing I tried when we discovered the not-hot shower situation. Confusingly there was a second plastic ring on the handle that I thought was the anti-scald, and when that didn't work, I could have sworn I tested turning off the cold supply to mixing valve to prove the valve wasn't the issue. Apparently my brain is turning to the same mush that is no longer hodling together the cracked areas of plaster in my walls.

Thank you for posting the fix. Was the previous owner or person that lived there elderly or disabled? It may have been set it that way to prevent scalding. Bathing hot water is between 100º-105ºF. Hot water pain threshold starts at 106-108ºF.

BTW, when checking temperatures at a faucet, if there is an aerator it can really drop the temperature more than you might think when a little room temperature air mixes with the water.

 

[Tomject]

Thank you for posting the fix. Was the previous owner or person that lived there elderly or disabled? It may have been set it that way to prevent scalding. Bathing hot water is between 100º-105ºF. Hot water pain threshold starts at 106-108ºF.

BTW, when checking temperatures at a faucet, if there is an aerator it can really drop the temperature more than you might think when a little room temperature air mixes with the water.

Previous tenants were millenials, and it's a shower without a tub, but good idea about elderly/tub setting. For measuring water temps. I filled a plastic cup and used an instant-read meat thermometer, didn't think about aeration causing temp drop.