NG furnace vs modern heat pump
- Thread starter Brett-EDH
- Start date
TomRc
TVWBB Pro
Your design temp is 91º according to the chart. In general, I hate “rules of thumb” and always do a full Manual J load calculation to size a system based on construction details, room size, and cfm requirements. However, for this exercise, let’s use the old-timer method and assume 1 ton of a/c for every 600 square feet of conditioned living space. It’s rudimentary and doesn’t take into account any of the climate conditions that a “design day” calculation would incorporate. Regardless, for the sake of discussion, we’ll say we have a 2400 sf ranch either on a slab or with an unconditioned basement. That puts us at 4 tons of air for the home. The Bosch product uses the same outdoor unit for 3-5 ton systems and you would match that up with their 4 ton rated indoor air handler or a furnace with a 4 ton blower in it. Furnaces blowers are often spoken of in terms of cfm instead of tonnage where 1200cfm = 1 ton. That puts your indoor blower requirement at 1600 cfm if we’re trying to match a traditional furnace to an inverter outdoor unit.
This is the important part...there is no concern in using an inverter system for air conditioning. They’re actually better at cooling than heating.
And, while we’re at it, please indulge me in a little bit of preaching. PLEASE engage the services of an HVAC professional who is willing and able to do a proper load calculation for sizing your system even if you are a do-it-yourselfer. Pay them for this single service if you have to. Some distributors provide load calculation services for free in an effort to earn your business when it is time to buy the equipment and associated parts. Find them and work with them. Too big or too small systems both have their problems and/or drawbacks. Your home is likely your largest investment and you’re probably spending 40%-50% of every day inside it. If your going to invest the money into one of these systems, invest in making sure it’s the right system and the right sized system along the way. Can I get an AMEN?
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Brett-EDH
TVWBB Hall of Fame
3 hallelujahs!
I’d rather pay for a professional calculation and then shop for a system that can handle my specific load needs. I’m certain the home builder undersized my units by a bit. We’ve gotten 21 years out of both systems.
My thoughts are the technology has increased efficiency so I stand to save on running costs and it makes sense to weigh which is the best technology to deploy now. Rebates are very common out here from the local utility.
And I see this as adding long term value to the home.
As usual though, some companies just seek to sell units and fail on an adequate design.
And the lingo is so above an average ordinary person. Like SEER.
For giggles I asked my next door neighbor what he installed in 2020 as he did a full system replacement. He doesn’t even know if he has a furnace or heat pump.
He asked me for a quick way to check and I said check the owners manual.
my last house had gas heat pump, it actually felt warm inside when below 20 degrees outside, now I have all electric and it is definitely not as effective....we hit -10f a month ago or so and it ran non stop along with a space heater but I never felt warm, I also have the option of wood heat but have not fired it up yet
We moved into our 1800 sq ft condo in 2013 in San Jose, and it still had the original odd-ball hydronic forced-air heating unit that passed water from the hot water heater through a heat exchanger, and a condenser on the patio for air conditioning. That hydronic system was actually quite efficient, but at 25 years old and my fear of it springing a leak and no one knowing how to service it, we decided in 2018 to switch to a Carrier Infinity system with a 5-stage heat pump and variable speed air handler. Our main need is heating during the winter, and we have no complaints in that department. Sometimes when it's running on Stage 1, it's so quiet you can't hear anything and just the slightest amount of hot air is coming out of the ceiling vents. We hardly ever run the air conditioning, it just doesn't get that hot here due to the orientation of our home to the sun, large overhangs on the building, and an upstairs neighbor that runs his AC all summer long and probably cools our unit below. But when needed, the AC works great, too, and on those rare occasions when it gets humid in the summer, it runs a dehumidifying cycle at really slow air speed that makes the house comfortable without chilling the house.
As for operating cost, there was a small increase in overall cost, using a bit more electricity but less natural gas, and it was also an intentional decision on our part to use less NG and more renewable electricity. Given our moderate climate, the system just doesn't have to work that hard to move heat from outside to inside. I would do our system again in a heartbeat. And it's cool that we can control it using our smartphones.
As for operating cost, there was a small increase in overall cost, using a bit more electricity but less natural gas, and it was also an intentional decision on our part to use less NG and more renewable electricity. Given our moderate climate, the system just doesn't have to work that hard to move heat from outside to inside. I would do our system again in a heartbeat. And it's cool that we can control it using our smartphones.
Bruno
TVWBB Honor Circle
TomRC. I’m a Pipefitter by trade and have run a ton of copper for HVAC, but never really understood the whole process. Very cool of you to share your expertise with us.
I live in a very mild climate not too far from Bret and Dan, but we have no AC in these parts.
Thanks for sharing all your info and like Bret I would totally do a deep dive to understand what is needed where.
I live in a very mild climate not too far from Bret and Dan, but we have no AC in these parts.
Thanks for sharing all your info and like Bret I would totally do a deep dive to understand what is needed where.
BFletcher
TVWBB Platinum Member
You most definitely have my praise on this. I don't want to distract from the excellent discussion on this thread but to my initial comment earlier I took matters into my own hands only after reaching my wits end from dealing with the original manufacturer's dealer and eventually moving-on to another and still ending with a malfunctioning unit. I live in a rural area and at the time was unable to find a company who was able to perform the work properly. And my little bit of study of the Refrigeration and AC lab manual was limited to performing repairs, not system design and load calcs, which I would never be able to comprehend
.
JohnTak
TVWBB Pro
My house is 3 years old and supposed to be energy efficient, it has a heat pump. The house is 95% electric so when the power is off I can only use the natural gas stove. I raised the thermostat from 67* to 68* and my bill jumped $100. I raised it from 68*to 69* and it jumped another $100. I hear natural gas has gone up so I don't know which is better. I dropped the thermostat back to 68*.
Brett-EDH
TVWBB Hall of Fame
PGE? Or another utility? My PGE NG bill was $342 this billing period. Quite expensive. Thus this new rabbit hole I’m digging.
We only use heat for a few hours a day. My early research is indicating I might only save $200-300 a year on moving to a HP for winter heating.
We rarely have outages with SMUD. Unlike our PGE friends.
LMichaels
TVWBB 1-Star Olympian
Knock wood the most energy usage I have is winter. In summer AC is rarely used for me unless it's extremely humid and hot or allergens are especially bad. Otherwise I relish being able to open the windows (except when I have to listen to neighbor's PIA dogs).
That aside I relish fresh air. Going so far that even in winter if we get somewhat mild temps (upper 30s and up) I will open up the house. Gas bill be damned
In any case thanks to adopting tankless water heater 17+ years ago, and super HE furnace and AC system, my energy costs are VERY tolerable. And my house is anything but efficient in terms of construction. It's built in 1981, and if you looked at it's construction you'd swear it was built by a bunch of drunken idiots (which I really thing it was). But over the years we've done some things to help. New siding with tyvek wrap, then foam board and then the siding, better windows (though back in 2003) and not top of the line (Crestline builder's grade vinyl), last spring had insulation blown into the attic to get it up to R50 level. Removing the drafty wood burning fireplace and installing the sealed gas burner with remote control. I think this change alone did more than nearly anything. As our family room is no longer like being in an icy wind tunnel, no more buildup of ice on bottom of patio door either, or around fireplace opening.
IDK for sure how many therms we use but I know it's gotta be WAY less. Because even now with energy prices at record levels our bills are WAY under what they were before these improvements and back when gas was dirt cheap.
Heck even our electric bill has dropped from the previous times when if we got a bill UNDER $200 we were shocked. Now, electric is typically not even $50.
I would absolutely HATE being an all electric home. Would never buy one. At least right now, with a small inverter generator if I lose power I can run 80% of my home (including the furnace) at once. Because I have cut the electric "footprint" of our house so much. Get an all electric and without a VERY large genset you are DOA. Not for this kid. And to top it off if you're all electric you won't have the fuel to run that large genset.
Try that when your gonads are turning to icicles
That aside I relish fresh air. Going so far that even in winter if we get somewhat mild temps (upper 30s and up) I will open up the house. Gas bill be damned
In any case thanks to adopting tankless water heater 17+ years ago, and super HE furnace and AC system, my energy costs are VERY tolerable. And my house is anything but efficient in terms of construction. It's built in 1981, and if you looked at it's construction you'd swear it was built by a bunch of drunken idiots (which I really thing it was). But over the years we've done some things to help. New siding with tyvek wrap, then foam board and then the siding, better windows (though back in 2003) and not top of the line (Crestline builder's grade vinyl), last spring had insulation blown into the attic to get it up to R50 level. Removing the drafty wood burning fireplace and installing the sealed gas burner with remote control. I think this change alone did more than nearly anything. As our family room is no longer like being in an icy wind tunnel, no more buildup of ice on bottom of patio door either, or around fireplace opening.
IDK for sure how many therms we use but I know it's gotta be WAY less. Because even now with energy prices at record levels our bills are WAY under what they were before these improvements and back when gas was dirt cheap.
Heck even our electric bill has dropped from the previous times when if we got a bill UNDER $200 we were shocked. Now, electric is typically not even $50.
I would absolutely HATE being an all electric home. Would never buy one. At least right now, with a small inverter generator if I lose power I can run 80% of my home (including the furnace) at once. Because I have cut the electric "footprint" of our house so much. Get an all electric and without a VERY large genset you are DOA. Not for this kid. And to top it off if you're all electric you won't have the fuel to run that large genset.
Try that when your gonads are turning to icicles
JohnTak
TVWBB Pro
My NG is PG&E about $25 per month to cook. My electric is City of Lodi, combo electric, water, sewer and trash. Cheaper than the other guy but going up.
TomRc
TVWBB Pro
Larry touches on a couple of points here that are valid for cold climate considerations and these reasons reinforce why many people in these areas are opting for a hybrid system (inverter heat pump outdoor unit with a traditional fossil fuel furnace) vs a full electric heat pump system.Knock wood the most energy usage I have is winter. In summer AC is rarely used for me unless it's extremely humid and hot or allergens are especially bad. Otherwise I relish being able to open the windows (except when I have to listen to neighbor's PIA dogs).
That aside I relish fresh air. Going so far that even in winter if we get somewhat mild temps (upper 30s and up) I will open up the house. Gas bill be damned
In any case thanks to adopting tankless water heater 17+ years ago, and super HE furnace and AC system, my energy costs are VERY tolerable. And my house is anything but efficient in terms of construction. It's built in 1981, and if you looked at it's construction you'd swear it was built by a bunch of drunken idiots (which I really thing it was). But over the years we've done some things to help. New siding with tyvek wrap, then foam board and then the siding, better windows (though back in 2003) and not top of the line (Crestline builder's grade vinyl), last spring had insulation blown into the attic to get it up to R50 level. Removing the drafty wood burning fireplace and installing the sealed gas burner with remote control. I think this change alone did more than nearly anything. As our family room is no longer like being in an icy wind tunnel, no more buildup of ice on bottom of patio door either, or around fireplace opening.
IDK for sure how many therms we use but I know it's gotta be WAY less. Because even now with energy prices at record levels our bills are WAY under what they were before these improvements and back when gas was dirt cheap.
Heck even our electric bill has dropped from the previous times when if we got a bill UNDER $200 we were shocked. Now, electric is typically not even $50.
I would absolutely HATE being an all electric home. Would never buy one. At least right now, with a small inverter generator if I lose power I can run 80% of my home (including the furnace) at once. Because I have cut the electric "footprint" of our house so much. Get an all electric and without a VERY large genset you are DOA. Not for this kid. And to top it off if you're all electric you won't have the fuel to run that large genset.
Try that when your gonads are turning to icicles
I actually bought into my all-electric property fully intending to add a natural gas line from the street to the home ASAP. As luck would have it, along came COVID and the world was put on pause. Accordingly, our uutility company put retrofit hookups on hold and I was forced to wait out the pandemic. Thankfully, I work for the largest plumbing & heating distributor in the northeast and have access to a large inventory of incredible deals on discontinued and/or scratch and dent equipment. For 7 ductless heads and 3 outdoor units, I’m all-in at less than $2500 for a self installed system including all of the ancillary installation parts and pieces. I was actually surprised to learn throughout that first winter that we could actually heat the home sufficiently under all but the worst of conditions using this system.
With COVID finally in the rear view mirror, we went ahead and completed the gas install to only then create a new problem for ourselves. With just a gas dryer and a Weber grill (go figure, right?) pulling NG, we weren’t using enough gas to overcome the utility minimum delivery and usage charges so, in essence, we’re paying for gas that we’re not using. I’ve now rectified that by picking up a small 2-stage 96% furnace with a forklift dent in the side of it for the crazy low price of $200. I set it up in our unfinished basement with a plenum on top of it to direct heat in a couple of different directions and it’s sole purpose is to allow to allow us to extend our conditioned living space down into that area for a home gym, etc. In the process, we have unconsciously made an additional step away from the current electrification push. My heat pumps aren’t going anywhere, though. They’re simply the most efficient air sourced solution for providing a/c to your home.
I should be watching this thread quite closely. We have a 1993 era NG furnace (original to the house.) I've replaced the flame sensor, the ignitor (have spares for both on the shelf,) and the draft blower so far. We've been contemplating a pro-active strike and putting in a new highest efficiency available NG furnace, but the numbers thus far really don't make sense yet. Yeah, we'd like to avoid a gotta replace it now situation.
Unfortunately, the south eastern corner of MN really doesn't allow much for heat pumps in the winter. I expect to spend a couple of weeks every year at -10 to -20 F (I do need to look for the design numbers suggested elsewhere in this thread.) The whole house is ducted, and it probably doesn't make sense to start using mini-splits here.
There is probably some truth the the push for full electrification...... burn petro at it's utterly most efficient for electric power generation (or renewables, like wind or hydro,) then wheel the electricity out to us consumers. NG..... with good burners that are properly adjusted, there shouldn't be much beyond CO(2) and water..... and I really like cooking over gas. I'm not quite willing to jump on that band wagon yet.
Unfortunately, the south eastern corner of MN really doesn't allow much for heat pumps in the winter. I expect to spend a couple of weeks every year at -10 to -20 F (I do need to look for the design numbers suggested elsewhere in this thread.) The whole house is ducted, and it probably doesn't make sense to start using mini-splits here.
There is probably some truth the the push for full electrification...... burn petro at it's utterly most efficient for electric power generation (or renewables, like wind or hydro,) then wheel the electricity out to us consumers. NG..... with good burners that are properly adjusted, there shouldn't be much beyond CO(2) and water..... and I really like cooking over gas. I'm not quite willing to jump on that band wagon yet.
What brand and when did you get three heat pumps and 7 heads for $2500? That seems crazy low. I'm a PM for a mech contractor as well as mechanical engineer. I will say our company seems to lean towards the Mitsubishi/Trane systems and I know they are very proud of them when they send invoices
We seem to see more of the LG/Mitsubishi VRF systems on the commercial side of things. Ever done the Bryant personal use program? I paid only $354 for a 9k high wall mount and heat pump. That was pre supply chain issues. Heck, I had more money in the 60' lineset/power cable than the unit
.With a good ducted system installed it is really hard to justify installing new heads throughout a home.
I would say MN will be one of the last to transfer out of NG. It's too dang cold for heat pumps to perform properly. Rochester internationally airport design day is -9F.
Remember the design temp is the percentage of hours warmer than the listed temperature. So 99% of the hours (87.6 hours in a year) are warmer than -9F.
Bingo. That's the number I should have been looking up myself. Rochester International is less than 50 miles to the south, I'd use that as a decent yardstick. 99% of hours above -9 F? Empirically..... yeah, I'd concur, it's actually lower than I would have guessed.
I do like our house...... but running anything like power cabling, network cabling, etc., will entail some fairly serious drywall and ceiling work as a rule (split bi-level, 3 half flights of stairs.) Replacing the HVAC in place makes a bunch of sense.
TomRc
TVWBB Pro
Daikin equipment purchased in 2020. My most expensive component was the 4 port outdoor unit that cost me $400. But again, I’m buying at pennies on the dollar for scratch & dent and discontinued models. The regular contractor price on a unit like that was $2800 at the time.What brand and when did you get three heat pumps and 7 heads for $2500? That seems crazy low. I'm a PM for a mech contractor as well as mechanical engineer. I will say our company seems to lean towards the Mitsubishi/Trane systems and I know they are very proud of them when they send invoices
Ever done the Bryant personal use program? I paid only $354 for a 9k high wall mount and heat pump. That was pre supply chain issues. Heck, I had more money in the 60' lineset/power cable than the unit
TomRc
TVWBB Pro
Agreed. With sustained temps below zero, your design temp is well below the 15ºF number that I use as a crossover point when considering inverter ducted systems vs fossil fuel furnaces.
TomRc
TVWBB Pro
Agreement here also. Ductless splits don’t make a lot of sense if you have a ducted system. However, the ducted inverter systems we began the discussion on would absolutely be a good candidate for consideration as a replacement for the a/c side of things if someone is looking for additional efficiency.