Natural Gas vs Heat pumps for heating

[Big Earl]

Thank you. I think mini split is great. Ducting allows me to connect to dehumidifiers and allow some other options as well.
What do you mean not using flexible duct? What is the other option?

Conventional metal duct.

Flexible vs. Metal Ductwork: Which Should You Choose? - Calaway Heating & Air Conditioning

The saying “out of sight, out of mind” couldn’t be truer when it comes to a building’s ductwork system. It’s easy to forget about air ducts when they’re hidden behind walls and in the basement. However, homeowners and business owners in St. George, UT must familiarize themselves with the...

calawayair.com

 

[h2ofun]

So if I'm going to construct a new house today (2 story, 6 bed) which would be better: ducted heat pump HVAC system or ductless mini split for each room?
I think the ducted system will allow me to tie up into a separate dehumidifier, ERV, air filtration and allow for normal looking air supply. The downside is that there will be loss in efficiency with the ducting. Thinking Mitsubishi VRF system.

The fall back is to use the traditional central air HVAC with ducting and zoning via damper. Then use a heat pump like Lennox XP25. This is less efficient and the zoning is less than ideal.

Any pointer?

I redid my house, got rid of all the ducting, and went 100% mini splits. Wife LOVEs it!!!!! I have 4 compressors and 10 heads

 

[miimura]

I would choose ducted for air quality. Hands down. If you are worried about efficiency, oversize the ducts, don't use flexible ducts, and insulate, insulate, insulate! (i.e. design the house so your ducts are in a conditioned space.)

All the best,

BG

This is the key thing that I would change about my custom built house. The insulation and air sealing was not nearly rigorous enough.
I would have changed the insulation strategy so that the attic was conditioned space so that the upper floor HVAC would not lose energy to the unconditioned attic. The lower floor HVAC does not have this issue.

 

[EL0NTRK]

Conventional metal duct.

Flexible vs. Metal Ductwork: Which Should You Choose? - Calaway Heating & Air Conditioning

The saying “out of sight, out of mind” couldn’t be truer when it comes to a building’s ductwork system. It’s easy to forget about air ducts when they’re hidden behind walls and in the basement. However, homeowners and business owners in St. George, UT must familiarize themselves with the...

calawayair.com

This is a bit much for residential, right?
I hate the flex duct as much as everyone but it seems the metal ducting only justify the cost on commercial building.
Besides the residential hvac guys may not know how to do it right.

 

[EL0NTRK]

I redid my house, got rid of all the ducting, and went 100% mini splits. Wife LOVEs it!!!!! I have 4 compressors and 10 heads

How are you dealing with dehumidifier, air quality, etc?
What system you used? Pics of outdoor unit and indoor heads?

 

[BGbreeder]

Thank you. I think mini split is great. Ducting allows me to connect to dehumidifiers and allow some other options as well.
What do you mean not using flexible duct? What is the other option?

You are welcome!

As in rigid metal ducts. "Old fashioned" style. Round, square, or rectangular. Pretty much the only thing that is used on commercial construction, and in many areas of the country. Flexible ducts have higher resistance to air flow, are more likely to get "kinked" during installation (further reducing flow), and are basically a consumable item that will need replacing in ten to fifteen years as the plastic liner wears out due to the flexing. I know flex is popular in Texas, but in many areas of the country, rigid ducts are the norm. I have no idea what the cost difference is in Texas.

All the best,

BG

 

[h2ofun]

This is a bit much for residential, right?
I hate the flex duct as much as everyone but it seems the metal ducting only justify the cost on commercial building.
Besides the residential hvac guys may not know how to do it right.

In Calif I guess I never have to worry about

How are you dealing with dehumidifier, air quality, etc?
What system you used? Pics of outdoor unit and indoor heads?

I never have had to deal with a dehumidifier. We have lots of smoke during fires I just leave the house closed. mitsubishi.

 

[EL0NTRK]

You are welcome!

As in rigid metal ducts. "Old fashioned" style. Round, square, or rectangular. Pretty much the only thing that is used on commercial construction, and in many areas of the country. Flexible ducts have higher resistance to air flow, are more likely to get "kinked" during installation (further reducing flow), and are basically a consumable item that will need replacing in ten to fifteen years as the plastic liner wears out due to the flexing. I know flex is popular in Texas, but in many areas of the country, rigid ducts are the norm. I have no idea what the cost difference is in Texas.

All the best,

BG

Got you. Seems like many they are done in TX in some custom home as well. Rigid duct for the main trunk and the short end using flex like in this video by a guy who is popular builder in TX who builds high performance houses.

 

[BGbreeder]

Yes, I have seen more than a few of his videos, but mostly they seem to give me the feeling that they are placements for particular companies. Still, some of the house he shows are clearly big budget and the owners are doing unusual and interesting things. I remember a memorable one lakeside compound that had enormous concrete piers being drilled, and some perfectionist concrete work.

Again, to me the issue with flex is that it wears out, which is often quite difficult to repair/service in residential settings. (Servicing a duct in a commercial drop ceiling with the last ten feet in flexible duct is trivial. And having a commercial tennant last fifteen years is unusual, so a ten year lifespan is not a problem. If Matt puts up a drywall ceiling in that 1940s house he is gutting, those ducts will be problematic to service, and they will need servicing much sooner than eighty years from now.)

HVAC duct suppliers make custom metal vents all day long. Supply isn't the issue. I think taking the time to design them is. Lucky for you, you are in the right phase to use all metal easily. Whether you want to, is your issue. The prior owners a house I know used all metal ducts, but then again they were in the HVAC business. On the other hand, they did half a job repiping by hooking up copper pipe to galvanized and leaving galvanized hidden in the walls, i.e. they did a half job that was destined to rust out quickly. Most of us have budgets to meet and that usually means trade offs, some are better than others (like half galvanized!).

All the best,

BG

 

[EL0NTRK]

Thanks everyone who has contributed to this discussion with their valuable input. I have learned a ton and definitely have a better idea of what is a good opportunity to get a house built right from scratch.

I have asked my builder to do this on our upcoming build. Keep in mind that this is a house in Houston so humid and hot.

Roof: put 3 layers of polyiso on the roof to insulate the roof. I can't do the metal roof due to HOA but will put concrete tile on it and later solar panels.
The attic will be spray foam and unvented. It will be conditioned.

https://www.finehomebuilding.com/pdf/021224084.pdf

HVAC: Mitsubishi VRF system with ducted (metal ducting) + Dehum + air filtration. Will combine this with several mini split for areas like garage.

Water heater: Rheem heat pump 80gal with recir pump in the attic.

Cooking: induction instead of gas.

 

[EL0NTRK]

Just to update you guys on this project.
My builder and I have met with 2 HVAC companies and soon a 3rd. They are all Mitsubishi Preferred Diamond contractors which means they have certain level of training and a 12 years warranty on parts. They will provide heat/load calculation and design for us and come up with a proposal.

It's going to be a fun experience building the house.

 

[Redhill_qik]

Water heater: Rheem heat pump 80gal with recir pump in the attic.

I had a Rheem hybrid electric 80 gallon installed 2 weeks ago in our garage and I would be very reluctant to put one of these in the attic. Efficiency wise it is working as expected and my natural gas consumption has dropped from 1.0 Therms/day to 0.08 Therms/day (just our cooktop and clothes dryer are using gas right now) and the electric use has been on target with my estimate at 3.2 kWh/day. Gas was costing me around $1.90/Therm and I'm giving up about $0.06/kWh in credits as a net generator, so $1.75 vs $0.19 is a savings of $1.56/day or $569.40/year.

Now the bad part is that a hybrid heat pump is noisy. I think that the Rheem has the lowest noise level on the market at 49dB, but this is still generates a very noticeable low frequency hum/drone/vibration and it will run for 2-3 hours to replace the hot water that was used from a shower in the preferred Energy Saver mode. My spouse is definitely not happy about the noise level. It does appear that over time we are starting to tune it out, but I can't imagine having this over a sleeping area.

One of the most important considerations for the recirculation system is that all of the hot water pipes going out are well insulated as well as the return pipes to minimize the heat loss. If you have the ability during construction make sure that this happens. I don't know if there is way to insulate pipes that might be in a concrete foundation, but if there is I would do that also as I think I am losing a lot of heat that way.

I also now have WiFi plug on the recirculation pump and I created an Alexa routine "Run Hot Water" to acknowledge the command, turn on the pump, wait 4 minutes, turn off the pump, and then announce that the hot water is ready. This has been working great.

 

[h2ofun]

Just to update you guys on this project.
My builder and I have met with 2 HVAC companies and soon a 3rd. They are all Mitsubishi Preferred Diamond contractors which means they have certain level of training and a 12 years warranty on parts. They will provide heat/load calculation and design for us and come up with a proposal.

It's going to be a fun experience building the house.

yep, that is what I have

 

[EL0NTRK]

I had a Rheem hybrid electric 80 gallon installed 2 weeks ago in our garage and I would be very reluctant to put one of these in the attic. Efficiency wise it is working as expected and my natural gas consumption has dropped from 1.0 Therms/day to 0.08 Therms/day (just our cooktop and clothes dryer are using gas right now) and the electric use has been on target with my estimate at 3.2 kWh/day. Gas was costing me around $1.90/Therm and I'm giving up about $0.06/kWh in credits as a net generator, so $1.75 vs $0.19 is a savings of $1.56/day or $569.40/year.

Now the bad part is that a hybrid heat pump is noisy. I think that the Rheem has the lowest noise level on the market at 49dB, but this is still generates a very noticeable low frequency hum/drone/vibration and it will run for 2-3 hours to replace the hot water that was used from a shower in the preferred Energy Saver mode. My spouse is definitely not happy about the noise level. It does appear that over time we are starting to tune it out, but I can't imagine having this over a sleeping area.

One of the most important considerations for the recirculation system is that all of the hot water pipes going out are well insulated as well as the return pipes to minimize the heat loss. If you have the ability during construction make sure that this happens. I don't know if there is way to insulate pipes that might be in a concrete foundation, but if there is I would do that also as I think I am losing a lot of heat that way.

I also now have WiFi plug on the recirculation pump and I created an Alexa routine "Run Hot Water" to acknowledge the command, turn on the pump, wait 4 minutes, turn off the pump, and then announce that the hot water is ready. This has been working great.

I have been reading about the noise issue and it seems the latest version (gen 3?) has it while gen 2 is quite. I read that Rheem identified the issue and fixed it already by changing some manufacturing process or part.
It's worthwhile to get it check and replaced. There should be no reason it should making noise that you can hear. Can you have a meter to check if it's still within spec of 49 db?

Definitely will try to remember the insulation issue running pipe. Are you using plex or copper pipes in your house?

 

[EL0NTRK]

it will run for 2-3 hours to replace the hot water that was used from a shower in the preferred Energy Saver mode. My spouse is definitely not happy about the noise level. It does appear that over time we are starting to tune it out, but I can't imagine having this over a sleeping area.

I also now have WiFi plug on the recirculation pump and I created an Alexa routine "Run Hot Water" to acknowledge the command, turn on the pump, wait 4 minutes, turn off the pump, and then announce that the hot water is ready. This has been working great.

How many people in the house? Do you ever run out of hot water? I'm a family with 2 young kids and I don't know if 80 gal is enough for our needs, taking long showers, doing laundry, etc.

On the automation note, I plan to have a presence sensor that will turn on the recir pump when you are in the bath area, etc. That will be part of my HA system that I plan to learn how to build in the new house.

 

[Redhill_qik]

I have been reading about the noise issue and it seems the latest version (gen 3?) has it while gen 2 is quite. I read that Rheem identified the issue and fixed it already by changing some manufacturing process or part.
It's worthwhile to get it check and replaced. There should be no reason it should making noise that you can hear. Can you have a meter to check if it's still within spec of 49 db?

Definitely will try to remember the insulation issue running pipe. Are you using plex or copper pipes in your house?

The manufacturing date was 09/2021, so if there was a manufacturing update then it should have been applied.

I downloaded a sound meter app and will measure when it kicks on again. I think that it is within the spec, but that level is definitely noticable and it goes on for hours.

 

[EL0NTRK]

If it's noticeable, then I have to make sure to insulate the attic floor or the ceiling of the rooms below to avoid the noise.
In my area, attic is the popular place to put the water heater since it's hot and you can get stronger water pressure when it's higher up.

 

[Redhill_qik]

How many people in the house? Do you ever run out of hot water? I'm a family with 2 young kids and I don't know if 80 gal is enough for our needs, taking long showers, doing laundry, etc.

On the automation note, I plan to have a presence sensor that will turn on the recir pump when you are in the bath area, etc. That will be part of my HA system that I plan to learn how to build in the new house.

Filled the large whirlpool tub (probably 60-70 gallons) yesterday and the water was still coming out hot at the end. I have it set up with the heater at 140F with a thermostatic mixer at the hot water heater that takes it down to 125F. It took me a while to get this setup correctly and I'm not a fan of a mixer setup, but it did work. Yesterday with the large usage it consumed 5.53 kWh versus up from 2.45 kWh the day before. It seems to have run for 3 hours to recover which is a match for the rated 27 gallons/hour recovery time.

Right now there are just two of us, but come Christmas there will be 6 which will be the real test. I plan on switching from Energy Saver to the High Demand mode that will use more of the electric elements. This is more to reduce the amount/length of noise than it is a worry that there won't be enough hot water for everyone.

I don't think that putting the recirculation pump on presence sensor is a good idea. You only want to run the recirculation for a little bit to get the hot water to the tap and then there is no need to run it for longer and some people spend a lot of time in the bathroom. You would want to at least couple this with a temp sensor on the pipe to reduce the amount of time that pump actually runs.

 

[Redhill_qik]

If it's noticeable, then I have to make sure to insulate the attic floor or the ceiling of the rooms below to avoid the noise.
In my area, attic is the popular place to put the water heater since it's hot and you can get stronger water pressure when it's higher up.

My installer had issues raising the heater around 30" off the garage floor as it was higher than the van floor. I can't image the issues with getting one up stairs and then through a hatch into the attic when it needs to be replaced. I guess a winch mounting point above the access point will take care of the last part.

 

[wwhitney]

you can get stronger water pressure when it's higher up.

While that would be true for an unpressurized tank providing only gravity pressure to your hot fixtures, it won't be true for a pressurized tank hooked up to city pressure or a well pump/pressure tank.

Cheers, Wayne