Confused - Hydronic air handler VS heat pump VS heat pump plus furnance
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For the heat pump, I would ask for a cold climate unit. Something like this:
or the 38MURA high heat* version of this:
These will heat down to your design temp so you have the option of running either gas or electric when cold.
Also make sure the furnce has an ECM blower. These are much quieter and use significantly less power. With the duel fuel setup, you don't need an expansive furnace as it should only ever run when very cold. A standard one or two stage unit is good enough.
*high heat is important. There are two version and the other version does significantly less heat at 5F.
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@Kaos Awesome - I just spoke with an installer that's Diamond, and he just mentioned Intelli-heat. Wonder if I can get my hands on some 410a equipment. I have to confirm, but it sounded like his idea was to use the intelliheat just for the first floor and leave the second as a regular heat pump.
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That is surprising because it seems that clean fill material would be desirable by someone
NJ Steam Homeowner.
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Definitely possible, and finding that person(s) is the way to reduce that cost.
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Here's a part two to the question: I had an installer mention that if I go duel fuel, just to do it on the first floor since heat rises and no need to do it for the second floor system. Make sense?
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If you agree with that logic why bother putting any heat at all on the second floor?
Yes, you can make such layouts work, such as many have used a single wood stove on the first floor and heated an entire house. But the house tends to have large temperature differences and you need to make adjustments in how you live just to make the system function at all.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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That is mostly correct espcially with doors open. One option is to look at the fuel burner as backup for polar vortex days. In that case the having it only on the main floor makes sense if it saves some cost. Just make sure the heat pump for the 2nd floor is sized properly to handle your 99% design load.
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Duel Fuel
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Duel fuel……..is that when you run the AC and the heat at the same time?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Only if you want really DRY Air 😁
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I want to follow up on the early part of the discussion where we talked about the role of infiltration in indoor humidity.
When it's cold out, the air outside will hold less moisture than the air inside the house. Infiltration will tend to take humidity out of the house. At the same time, the occupants of the house generate humidity through activities like bathing, cleaning, cooking, breathing and perspiration. The humidity level in the house will stabilize when the moisture lost through infiltration balances the humidity added through occupant behavior.
This graph shows infiltration rate (on the x-axis, in CFM) versus equilibrium humidity (on the y-axis, in percent):
It assumes an indoor temperature of 70F. The three lines are for outdoor temperatures of 0F, 20F and 40F, all at 50% relative humidity outdoors.
Manual J assumes that occupants produce an average of 0.2 pints per hour, this chart assumes four occupants.
Note that at very low infiltration rate — as in a very tight house — even in winter humidity can get uncomfortably high. The ideal infiltration rate seems to be around 40 CFM.
Usually when infiltration is measured it's measured using a blower door test and expressed in air changes per hour. To convert that to CFM you need to know the volume of the house. Also, the blower door pressurizes the house, so you have to apply some sort of correction to account for the pressurization.
Just to put these numbers in context, 40 CFM is 2400 cubic feet per hour. A 3,000 square foot house with 8' ceilings is 24,000 cubic feet in interior volume, so that's 0.1 air changes per hour. A very rough rule of thumb to convert from blower door scores to natural air changes is to divide by 20, so that would be equivalent to a blower door score of 2.0 ACH. In 20th century construction that would be pretty much unheard-of, but in modern construction that's a very achievable level of tightness.
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Main floor is effectively open floor plan - living room, central cooridor with mudroom/half bath/hall, then kitchen and living connected. Second floor is three bed, two full bath, and a laundry room.
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I'm a dual fuel skeptic. In order for it to make sense to switch between gas and electric depending on the outdoor temperature they have to be close in price anyway. If they weren't, one would just be cheaper all the time. But if they're close the amount of money saved by switching is going to be small, not enough to justify the added complexity and cost.
The advantage a furnace has over a heat pump is that it produces hotter air, so it can output the same amount of heat with smaller ducts. This is a real advantage, especially in a retrofit where the ducting is already there, but in any house no one wants to give up space for ductwork unnecessarily. Usually when dual fuel is proposed what is envisioned is that gas is going to be used on the coldest days, regardless of relative prices, because the system as installed won't be able to meet the heating load using the heat pump.
Sure, the heat pump can provide heat in mild weather, but you don't need that much heat anyway in mild weather so you're not saving that much money.
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Dual fuel has a place DC, for the constraints. Ductwork is one. An electric panel is another as is cold climate performance. I agree that switching to save on costs is a bit of a loser. The prices change a lot and you have to be ON IT to know the current monthly price of each
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Just to be clear we're talking about the same thing, when I say "dual fuel" I mean a system that can heat using either a heat pump or a furnace, not a furnace for heating and a heat pump for cooling.
If the heat pump being installed can't heat the house by itself, it's kind of a sham dual fuel. You don't really have the choice of choosing your fuel, you have the choice only in warmer temperatures. And I think we both agree that the cost savings from that are minimal.
Now, in a lot of cases installing a heat pump instead of just an air conditioner adds little or nothing to the total cost. So adding a heat pump instead of just an AC is a selling point, it's now a "dual fuel" system. But it's not like this is really doing the customer any favors.
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I think dual fuel includes cases where the heat pump alone can’t cover 100% of demand. In that situation, the furnace is competing against resistance backup too. But I see your point. I still think dual fuel has value for the constraints. That’s not a sham. Using a heat pump for 80% of outdoor temps, which is likely 95+% of total heat needed, is still substantial.
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I did a detailed analysis for Boston, MA, you can see it here:
Look at the tab labeled "Analysis."
The house in question would have an estimated annual heating bill of $2,037.47 if it was heated with a heat pump, with electrical resistance used when the heat pump lacked enough capacity.
I ran three scenarios:
- Burning oil instead of using resistance heat for supplemental heat. This would save $10.47 per year.
- Burning oil below the breakeven temperature (10F). This would save $21.92 per year.
- Burning oil below 25F (picked arbitrarily as something that felt about right). This would save $9.51 per year.
Now, every house is different and energy costs vary tremendously from region to region. But the takeaway that the savings from dual fuel are just miniscule is something that applies broadly.
The reason is that you're only going to be considering dual fuel if the two fuels are reasonably close in cost. Boston is expensive, oil is expensive, so the breakeven temperature is pretty low there, 10F. But most places it's between 20F and 30F. And if the breakeven temperature is, say, 25F, electricity is going to be cheaper at 35F, but it's not going to be that much cheaper. And electricity is going to be more expensive at 15F, but it's not going to be that much more expensive. And the annual savings from switching fuels to chase the lowest cost is going to be less than the cost of a filter change.
Now, if you live some place where the fuel costs are radically different — let's say your breakeven is 50F, or -25F — you're not even going to be thinking about dual fuel, you're just going to run the cheaper one all the time.
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The reason is that you're only going to be considering dual fuel if the two fuels are reasonably close in cost.
I disagree! I think if you want to go dual fuel for energy savings, sure, the savings are likely minor.
But there are absolutely other great reasons for dual fuel.
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"But there are absolutely other great reasons for dual fuel."
The reasons given so far are for choosing gas over heat pump, not for dual fuel. What's a "great reason" for running a heat pump part of the time instead of gas all the time if it doesn't save any money?
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a few notes:
- Dual fuel can use fuels other than gas. Oil and propane can be particularly pricey, so savings could be better.
- sometimes people want a heat pump over just a furnace. Dual fuel can help accommodate them
- the price of AC + furnace can be the same as HP + furnace, so it’s an easy hedge against future fuel cost changes
- Dual fuel can enable a cheap furnace + cheap heat pump since the weaknesses cancel out.
As to why dual fuel can make sense instead of exclusively heat pump:
- #4 from above
- Helps with constraints: generator capacity, electric service capacity, airflow capacity, etc
- Can provide low temp performance
- Can reduce low temp emissions
- can be an easier sell to installers, insurance, homebuyer, electric utilities, etc
all that said, I have only a heat pump :).
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I'm sorry, but you should know better. It's a myth that one kind of heating system dries the air more than another. It's a misconception that the heating system is what's responsible for the air getting dry. It's caused by infiltration of cold outdoor air.
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Hydronic air handler VS heat pump VS heat pump plus furnace
Subtle pros and cons to every option. It's easy to get bogged down!
"I'm sorry, but you should know better. It's a myth that one kind of heating system dries the air more than another. It's a misconception that the heating system is what's responsible for the air getting dry. It's caused by infiltration of cold outdoor air."
»It is possible for the air system to induce more infiltration, though.
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Did I miss where this guy lives?
I never understood the boiler running to two air handlers and nothing else .. this seemed to grow out of a "this old house" episode and it never made sense unless NOTHING else was possible. High cost with poor control when stacked up against the other possibilities.
In the states where I live to get the rebates you have to get a heat pump and not a straight AC … even in NJ where I have natural gas and the NG is cheaper to use for heat. I have a heat pump that is never used.
Seems like the homeowner has natural gas … you want to keep that. Adding a boiler to a house without one is expensive. The new equipment makes zoning easy but you need to get someone who knows what they are doing and that's the hardest part .. the number of trades people who still say put in two systems when one will work is surprisingly high.
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You're on it - zone 5a east coast. I would like to keep the NG and that is the approach, but I am understanding that with Mitsu HH, intelliheat itsn't needed as we are temperate enough for the HH unit alone to provide adequate heating down to ~10-15F.
Let's take a boiler out of the equation as we now know that really doesn't make sense. I still want two systems, one for first and basement, and one for second and attic. The idea is to duct the first with a handler in the basement and throw a minisplit in the basement in order not to combine air with first (Mitsu HH systems lets you mix and match ducted with mini split heads). I would then do the same approach with a handler in the attic and put a split in the attic.
My three major questions include 1. Do I do a duel fuel (Intelliheat) or just go straight up traditional furnace and AC, 2. Do I go straight heat pump, and 3. How to size it because I had a Diamond installer tell me I need two 3-ton systems for each floor and we are talking 1,100 fully renovated/new. My load calc is getting me closer to 3 ton on first and 2.5 ton on second.
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I'm going to repeat my contention that dual fuel never makes sense. Or rather, rarely and under very specific circumstances: electricity is much cheaper than any other heat source, but you are unable to use a heat pump for all of your heating needs because of some constraint, like existing ductwork or limited electrical capacity.
Dual fuel is installed when the installer doesn't believe in heat pumps.
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Just a few random observations..
First, if you are going to install air conditioning, make it a heat pump (unless you are far enough south to never need heat). Why not? The cost difference is minimal.
Second, each situation is different. If you are dealing with a house with poor or no ductwork — surprising how many of those there are — anything on the heat pump side of the game other than minisplits is probably not in the cards. But see the previous paragraph.
Third, be very careful about costs. The cost and availability of energy sources (natural gas, LP, oil, electricity primarily) varies widely from place to place, and thus the economic viability of selecting one source, or a combination of sources, will be different. In Cedric's area, for instance, a heat pump always costs more to run, per BTUh delivered, than Cedric's big oil burner. There is no "break even" temperature. In other locations, a heat pump may well be less expensive to run even down to the lowest temperatures encountered.
Then there are local political considerations. Is the cheapest source even available for new or retrofit? Is it permitted? Are there subsidies and, if so, what are their requirements? And so on.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
First, I am running steam on NG, so not sure whether or not a heat pump is going to be cheaper as I am undergoing insulating and sealing the home. Is there a way to back into that by using currently utility costs per killowatt hour and therm?
Also, thank you both, as your comments overlap in a helpful way; meaning, I should decide whether or not I am going heatpump (all electricity) or NG heat plus condenser-based AC.
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@Toasted : "First, I am running steam on NG, so not sure whether or not a heat pump is going to be cheaper as I am undergoing insulating and sealing the home. Is there a way to back into that by using currently utility costs per killowatt hour and therm?"
To do an apples-to-apples comparison you take the unit cost of the fuel and multiply it by the efficiency of your heating device. What's tricky is that gas and electricity are sold in different units, gas is typically sold in therms which is 100,000 BTU. Electricity is sold in kWh which is 3412 BTU.
The efficiency of a gas burner is going to be somewhere between 60% and 95%. It should have a label on it with input and output BTU/hr, that's the efficiency. Efficiency of a heat pump varies with temperature, it's typically around 100% in sub-zero weather and 500% or more in the 50's. Efficiency for heat pumps is expressed as coefficient of performance, or COP, which is the percent efficiency turned into a real number; i.e. 3.1 COP means 310% efficiency.
The way I like to do it is to take the cost per therm and boiler efficiency, along with the cost of electricity, and calculate what the COP would have to be for both sources to cost the same, this is the break-even COP. Then look at the performance stats for the heat pump and figure out what temperature corresponds to that COP, that's the break-even temperature. Then look at historical weather data for the area to see how much time is spent above and below the break-even temperature.
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A heat pump costs essentially the same as AC. I see no compelling reason to lock yourself into only 1 fuel. Prices change.
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Here is a calculator that performs the conversion that DCContrarian mentioned:
Trying to keep Bernie burning!
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