Author Topic: Water Heaters & HVAC  (Read 1382 times)

NorCal

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Water Heaters & HVAC
« on: October 03, 2021, 12:22:31 PM »
I started discussing this in an unrelated thread, but figured I'd create my own topic after inadvertently hijacking someone else's thread.

I'm looking for some personal advice on my water heater and hvac setup.  I just had a contractor out on Friday to make some recommendations.  I liked the guy (he was highly recommended by a neighbor), and he had some reasonable ideas.  I'll get multiple quotes once I have a better idea of what direction I should go. 

I have several inter-related goals:
1. Save money on utility bills.  We plan to upgrade our solar system in a year or two when it's time to replace our roof.  I'd like to bake in any reasonable energy savings before I pay for solar panels.  Given the current payback on solar panels, I consider any efficiency improvements to be financially justified if they have a simple payback period of 10yrs or less.
2. Electrify where practical:  Given the direction of the power grid and larger decarbonization efforts, I see the writing on the wall for natural gas.  However, I'm learning that this is a lot easier said than done.  I'm willing to pay some premium to make this happen, but not a massive premium.
3. Improve summer comfort in our upstairs bedrooms.  It's pretty much impossible to cool our upstairs in the summer.  I believe this is equally caused by rising heat in the house, and a very hot attic from direct sunlight.

My current system:
1. A tank gas water heater with a re-circulation pump on a timer.  The timer does nothing for energy savings, as hot water flows through the system 24 hours a day without aid from the recirculating pump.
2. A gas furnace rated at 92% efficiency, but starting to show some wear.  The recent service I did has it running at 88% efficiency.
3. A typical AC unit.

I have a pretty good estimate of where my money is going.  This is how my annual bill is split (assuming 0.12.kwh & $0.7/therm):

Hot Water Heater: 24% (~50% of this is due to heat loss from the re-circulation system).
Furnace: 22%
Air Conditioning: 13%
Everything Else: 40%

I put the highest priority on that hot water heater.  Given the recirculating system, I don't think there's any reasonable electric options.  I understand that the hybrid/heat pump systems don't work well with a re-circulation system.  The contractor recommended a tankless gas model that has a demand based re-circulation pump.  It has wifi connected buttons or sensors that you put near the showers to manually turn on the re-circulation system when needed.  Completely turning off the re-circulation system isn't a great option, as it's a long loop, and it does take multiple minutes to get hot water to the master shower.

While I'd love to put in a heat-pump eventually, the contractor told me that they only work down to 15 degrees.  We get a number of days below this.  I know this is an area that technology is changing fast and contractors are fairly conservative on new technology (many times for good reason).  Are there any options here I should look at specifically?  I started going down the internet rabbit-hole, and ended up more confused than enlightened.

The contractor also recommended putting our AC/furnace on different zones.  This should help with both the bills and the upstairs comfort.  The house is already ducted and wired for it, we just need dampers and a controller.  The downside is that any controller will likely be incompatible with a future hvac upgrade.

We are also getting quotes for a whole-house fan to help with comfort in the summer, and it should reduce the AC bill a bit.  I don't think it will pay for itself in 10 years, but the added comfort may make it worth it.

Are there any recommendations on other things we should be looking at? 

YttriumNitrate

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Re: Water Heaters & HVAC
« Reply #1 on: October 03, 2021, 12:48:57 PM »
If you want to go the full electric route, you might want to look into a geothermal loop. They're usually not cheap, but it increase the efficiency of your AC and heat pump.

Also, heat pumps can work below below 15F, but maybe not the ones the contractor was used to installing.

Glenstache

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Re: Water Heaters & HVAC
« Reply #2 on: October 03, 2021, 12:57:57 PM »
Geothermal are expensive to install and generally the cost effectiveness scales with square footage. They tend to be installed either in trenches (takes room), or in vertical wells with a closed loop in the boring.
Changing the thermal loading is generally the most cost effective thing to do. Have you maximized your insulation, especially in the attic space and things like low-e windows? Solar panels should decrease the solar heating of your roof (shade!) as a hidden benefit.
Is your recirculation system on at all times? They are a worthwhile system in drought-ridden CA, but if you are losing that much water, maybe a different system is appropriate? My brother has a system where he turns the water on briefly and then off. That activates the recirc system and he then turns on the (now hot) water about 30 seconds later.
Ive got a heat pump hybrid water heater that I love. In summer it vents into my garage acting as free AC for that space.

NorCal

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Re: Water Heaters & HVAC
« Reply #3 on: October 03, 2021, 01:21:37 PM »
Geothermal are expensive to install and generally the cost effectiveness scales with square footage. They tend to be installed either in trenches (takes room), or in vertical wells with a closed loop in the boring.
Changing the thermal loading is generally the most cost effective thing to do. Have you maximized your insulation, especially in the attic space and things like low-e windows? Solar panels should decrease the solar heating of your roof (shade!) as a hidden benefit.
Is your recirculation system on at all times? They are a worthwhile system in drought-ridden CA, but if you are losing that much water, maybe a different system is appropriate? My brother has a system where he turns the water on briefly and then off. That activates the recirc system and he then turns on the (now hot) water about 30 seconds later.
Ive got a heat pump hybrid water heater that I love. In summer it vents into my garage acting as free AC for that space.

Our insulation is pretty good.  The home was built in 2010 with good attic and wall insulation.  I think the windows are the weak point, but not such a weak point that it would be worth the cost to upgrade.

I have the recirc pump on a timer, so it only runs in the mornings and evenings.  However, the hot water in the system naturally rises and the cold water naturally falls.  Water is actually moving through the system 24hrs a day.  This forces the hot water heater to kick on about 10 minutes every hour.  The water heater would only turn on ~2-3 times a day if I shut off the valve to stop the water from flowing.  Per the contractor, a "demand based" recirculator will eliminate this problem.  This is inline with information I found on the Energy Star website as well.

Interestingly, your comment inspired me to do some more digging, and it appears that there are special valves that can be installed to prevent the "thermosyphon" effect in these systems, which seems to be the problem I'm having.  I think a heat-pump type system might be feasible if I can stop this constant circulation.  I'll have to research this some more.

uniwelder

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Re: Water Heaters & HVAC
« Reply #4 on: October 03, 2021, 04:19:41 PM »
Can you explain the plan with solar panels?  You said the house was built in 2010 and you intend to replace the roof in a couple of years.  That sounds premature.  What kind of roof do you have and why do you think it needs to be replaced?  Also you said you want to upgrade your panels.  Does that mean there are panels currently installed?  If so, I wouldn't replace them unless roof square footage is limiting your ability to add more panels.

Also, heat pumps definitely function below 15 degrees.  As mentioned by @YttriumNitrate the contractor probably just isn't accustomed to them.  Companies that build mini splits (Mitsubishi, LG, etc) also make units in an air handler configuration, so you can connect the indoor unit directly to your ductwork, and there is no backup resistance heat coil needed.  They can function down to -5F at full capacity.  Better quality heat pumps from traditional brands can do the same.  I'm about to upgrade the heat pump at a house we're in the process of buying.  With the cold weather efficiency of new air heat pumps systems, I don't think geothermal is regarded as cost effective anymore in moderate climates.

NorCal

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Re: Water Heaters & HVAC
« Reply #5 on: October 03, 2021, 05:23:22 PM »
Can you explain the plan with solar panels?  You said the house was built in 2010 and you intend to replace the roof in a couple of years.  That sounds premature.  What kind of roof do you have and why do you think it needs to be replaced?  Also you said you want to upgrade your panels.  Does that mean there are panels currently installed?  If so, I wouldn't replace them unless roof square footage is limiting your ability to add more panels.

Also, heat pumps definitely function below 15 degrees.  As mentioned by @YttriumNitrate the contractor probably just isn't accustomed to them.  Companies that build mini splits (Mitsubishi, LG, etc) also make units in an air handler configuration, so you can connect the indoor unit directly to your ductwork, and there is no backup resistance heat coil needed.  They can function down to -5F at full capacity.  Better quality heat pumps from traditional brands can do the same.  I'm about to upgrade the heat pump at a house we're in the process of buying.  With the cold weather efficiency of new air heat pumps systems, I don't think geothermal is regarded as cost effective anymore in moderate climates.

The roof is a bit of an outlier.  Builders in our neighborhood used the cheapest roof materials possible and we live in an area where hail damage happens a LOT.  We are one of only 2-3 houses on our block that hasn't had a roof replaced yet.  Going up 1-2 grades in material quality is the difference between a 10yr and a 20yr+ roof in this area.

Our current solar system that came with the house offsets about a third of our electricity usage.  I'd like to get to a full offset, and I'll figure out the details at the time.  I have oldish Enphase equipment, and they are offering a ~50% discount to upgrade to newer inverters and modules.  With the increased efficiency of newer modules, I'll do the math on whether it makes sense to just add new panels, or to use the upgrade offer.  I'm not too concerned about the details today, as I'm sure the market will change by the time I'm ready to do something about it.

Good to know about the heat pumps.  I will look for contractors that are familiar with those brands.

uniwelder

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Re: Water Heaters & HVAC
« Reply #6 on: October 04, 2021, 06:28:56 AM »
Good to know about the heat pumps.  I will look for contractors that are familiar with those brands.

This is what I'm looking for my hvac guy to quote for me---- https://www.acwholesalers.com/LG-LV241HV4/p102721.html
$3,700 for 2 ton unit online.  Its unclear whether it'll be covered by warranty if I purchase.  Whether I buy online or have him buy will depend on the price difference.  Last time, he purchased a mini-split from his regular local distributor, I did most of the installation, and he did final hookup.  Cost of the unit through him was $400 more than if I bought it online, plus $300 hookup charge, so I'm expecting about the same thing this time around.

A more conventional brand would be something like Carrier Infinity.  There shouldn't be any need for electric resistance backup.

Fishindude

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Re: Water Heaters & HVAC
« Reply #7 on: October 04, 2021, 07:23:03 AM »
As noted above, your best investment would be in insulation and weather sealing.    Just because the home is rather new, does not mean they super insulated it.   In all likelyhood you could add insulation to attic and improve things as well as do a better job weather stripping all of the doors.    Windows are a big job, but you can replace a few at a time as budget allows.

That hot water recirculating pump is not something that is "needed".   I'd do away with it.

I don't think it would pay to upgrade the furnace & AC equipment until they fail.   If you have sloppy ductwork installation (lots of flex duct, or uninsulated where it should be) it can greatly reduce your systems efficiency.

We've currently got a water source heat pump and I would not recommend it.   I'm going back to a conventional furnace /  AC system.
These heat pumps do not put out "warm" air in the winter, so the house feels cold all the time.   It also seems kind of ridiculous to be constantly pumping water.   Our gas bill went way down with this, but the electric went up, so no significant savings.


Jon Bon

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Re: Water Heaters & HVAC
« Reply #8 on: October 04, 2021, 07:34:05 AM »
Fishindude has good points.

Are you sure about your Hot water tank usage? Maybe your pump adds a bunch of cost for some reason? Are you using it for radiant heat or something like that? A super cheap water tank costs about $200 a year, which if that is 25% of your total usage I feel like your are chasing a high investment for a low return. I would check into that. You might give your furnace a tune up for about $100 bucks. you can always just shop vac out as much of your ducts as possible. That would also help.

AC might be marginal to replace, if its a contractor grade unit you might see some savings. I just don't see how replacing perfectly good equipment saves you money or saves the planet.

Oh and go buy a temp gun, they cost $10 and is an awesome tool/toy. Just go around in the winter and find all the leaks, it's a fun job for sure. For instance I did all my rim joists last winter, they were between 50-35 degrees. So yeah then I put a lot of insulation in there and they were instantly 60-70 degrees. Some libraries even will lend out much more expensive temperature/infrared cameras.

Sibley

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Re: Water Heaters & HVAC
« Reply #9 on: October 04, 2021, 08:16:39 AM »
From recent experience with my house:

-adding film (to block/reflect heat) to the direct west facing windows made a noticeable difference in room comfort.
-replacing the black roof with lighter grey made a noticeable difference in the 2nd floor temps.
-adding 18 inches of insulation to the attic made a noticeable different in the 2nd floor temps. I just did that this year so haven't gone through winter yet, but I expect my heat bills to be lower. I'm also hoping I won't have ice dams this winter.

Between the 3 things, I think I've dropped the upstairs temps about 10 degrees in summer. That's before A/C. The back bedroom has dropped about 15 degrees on summer afternoons (the window film made a HUGE difference in that room, but it was limited to that room).

Other things that helped upstairs was closing up the multiple holes in the closets that had cables coming in from outside, and caulking around the windows as I repainted each room/window.

yachi

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Re: Water Heaters & HVAC
« Reply #10 on: October 04, 2021, 08:19:30 AM »
They can function down to -5F at full capacity.

Heat pumps are fascinating.  While resistance heating can have an efficiency of 1, putting out a KW of heat for every KW of electricity used, a heat pump can have an efficiency greater than 1.  It does this by using the latent heat in the outside air.  As it does its thing, the system will have coils outside that are colder than ambient air.  Your outside system has a minimum working temperature.  The higher the difference between the outside temperature and this minimum, the more energy is available in the outside air to heat your home.

Since you look ready to pull the trigger soon, here are some cautions:

The LV241HV4 you linked to has 3 performance points published for heating:

Outdoor 17F (DB) / Indoor 70F (DB) 26,000 BTU/h
Outdoor 5F (DB) / Indoor 70F (DB) 23,600 BTU/h
Outdoor -4 F(DB) / Indoor 70F (DB) 20,760 BTU/h

It's nominal capacity is 24,000 BTU BTU/h

It has very good heating, even at -4F, performing at 86.5% of its rated capacity, but it does have a reduced capacity.  (note this does not mean your system is less efficient at -4 than it is at 5, because you're asking it to work harder)

The other thing happening at colder temperatures is your house's heat losses are increasing.  They are generally proportional to the difference in temperature.  At -4F, you have 13.8% more heat loss than you do at 5F.

It's rather unfortunate that the performance of a heat pump goes down just as you need it the most, but that's physics.  You can either upsize the unit from your normal conditions so you have adequate heating at the minimum temperature condition (but more heating capacity than you need most of the time) or you can add a resistance heater to help with those very cold, non-design days.

One last thing to note:  You don't want to operate outside of the operating range.  I wouldn't be surprised if the heat pump controls refuse to let it operate below -4F, to protect the system from frosting.  That would mean a hard no-heat cutoff at -4F, unless you have some resistance heat.

uniwelder

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Re: Water Heaters & HVAC
« Reply #11 on: October 04, 2021, 08:45:34 AM »
They can function down to -5F at full capacity.

Heat pumps are fascinating.  While resistance heating can have an efficiency of 1, putting out a KW of heat for every KW of electricity used, a heat pump can have an efficiency greater than 1.  It does this by using the latent heat in the outside air.  As it does its thing, the system will have coils outside that are colder than ambient air.  Your outside system has a minimum working temperature.  The higher the difference between the outside temperature and this minimum, the more energy is available in the outside air to heat your home.

Since you look ready to pull the trigger soon, here are some cautions:

The LV241HV4 you linked to has 3 performance points published for heating:

Outdoor 17F (DB) / Indoor 70F (DB) 26,000 BTU/h
Outdoor 5F (DB) / Indoor 70F (DB) 23,600 BTU/h
Outdoor -4 F(DB) / Indoor 70F (DB) 20,760 BTU/h

It's nominal capacity is 24,000 BTU BTU/h

It has very good heating, even at -4F, performing at 86.5% of its rated capacity, but it does have a reduced capacity.  (note this does not mean your system is less efficient at -4 than it is at 5, because you're asking it to work harder)

The other thing happening at colder temperatures is your house's heat losses are increasing.  They are generally proportional to the difference in temperature.  At -4F, you have 13.8% more heat loss than you do at 5F.

It's rather unfortunate that the performance of a heat pump goes down just as you need it the most, but that's physics.  You can either upsize the unit from your normal conditions so you have adequate heating at the minimum temperature condition (but more heating capacity than you need most of the time) or you can add a resistance heater to help with those very cold, non-design days.

One last thing to note:  You don't want to operate outside of the operating range.  I wouldn't be surprised if the heat pump controls refuse to let it operate below -4F, to protect the system from frosting.  That would mean a hard no-heat cutoff at -4F, unless you have some resistance heat.

Yeah, sorry, I was being a little sloppy when writing that--- positive 5 vs negative 5.  Thanks for looking out and checking.  Heating design temperature in my area is +15F, so doesn't actually matter in my case.  Overall, the LG system has a very flat heat output as you mentioned.  When I was looking up specs for cheaper heat pumps, output at +17F was about half the nominal amount at about +40F, so it would be running into backup heat in that scenario, unless the heat pump was ridiculously oversized.  In my case, I'm looking to replace the old 3 ton system with this 2 ton version (along with extra attic insulation), which ends up being convenient for duct sizing as well.

edited to add--- again being a bit lazy to properly look this up, but I think the Mitsubishi Hyper-Heat units or equivalents of other brands do truly operate at 100% in the negatives.  Either way, outside the temperature range for most people to care about.

edited to add some more---- I got over my laziness.  The low temp version of the LG unit (LV241HHV4) is capable of 24,250 BTU at -4F with COP of 1.53 and 21,590 BTU at -13F with COP of 1.33.
« Last Edit: October 05, 2021, 05:37:16 AM by uniwelder »

nessness

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Re: Water Heaters & HVAC
« Reply #12 on: October 04, 2021, 03:34:43 PM »
Have you checked to see if your electric company is offering any rebates? Ours if offering significant rebates both for switching to electric water heaters and electric heating right now.

I'm not sure if you're considering an electric furnace, but I'd advise against it. I had electric heat (and electric everything else) when I lived in Denver. According to the people who serviced it, it was one of only a few all-electric houses in Denver, and for good reason - we kept the house at 62 degrees in the winter and our winter electric bills were still over $300/month at times.

uniwelder

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Re: Water Heaters & HVAC
« Reply #13 on: October 05, 2021, 03:20:11 PM »
somewhat related, MMM has a new posting about his diy heat pump installation--- https://www.mrmoneymustache.com/2021/10/05/diy-heat-pump/

NorCal

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Re: Water Heaters & HVAC
« Reply #14 on: October 06, 2021, 07:02:22 AM »
Have you checked to see if your electric company is offering any rebates? Ours if offering significant rebates both for switching to electric water heaters and electric heating right now.

I'm not sure if you're considering an electric furnace, but I'd advise against it. I had electric heat (and electric everything else) when I lived in Denver. According to the people who serviced it, it was one of only a few all-electric houses in Denver, and for good reason - we kept the house at 62 degrees in the winter and our winter electric bills were still over $300/month at times.

Yep!  Our I believe our utility rebate for a hybrid is $400, and a small tax credit on top of that.  The rebate for a tankless is only like $25.

The modern heat pumps are a far cry from the old electric resistive heaters, but the contracting world hasn't fully figured them out yet.  MMM's brand new article on the topic summarizes them much better than I can.

Somewhat off topic, Denver has some very aggressive climate related zoning codes proposed for new buildings.  It's fascinating what they've come up with.  While the developers aren't publicly supporting it, they're not fighting it either.  Essentially, all newly built homes would have to be "net-zero".  They would be all electric with enough solar panels to cover the annual utility bills.  Developers say it would cost about 2% more to build a home this way (which is much cheaper than retrofitting), but it would reduce annual utility costs to near zero.

somewhat related, MMM has a new posting about his diy heat pump installation--- https://www.mrmoneymustache.com/2021/10/05/diy-heat-pump/

This is a pretty amazing project.  Thanks for sharing!