What is the state of the art in the world of forced (scorched) hot and cold air?

vtfarmer

I posted here about the baseboard to CI rad retrofit I put into my old Vermont farmhouse some years ago and proudly take credit for the hundreds of pounds of copper pipe and sweat fittings making up a primary/secondary loop system with two boilers (oil and outdoor wood) controlled by a half dozen antique Honeywell T87 and 86 mercury thermostats which I regard as the apex of winter weather indoor comfort. I am one of these northeasterners who scoff air conditioning as a needless waste of electricity any place north of Maryland.

Ah, how the tables have turned. I now find myself for family reasons loading my farming operation onto a few tractor trailer loads as I trade my farm in the hills of Vermont for a farm in the hills of western Virginia. The land of forced hot air, heat pumps, and A/C.

What is the state of the art in the field? If I'm buying a house with an LP gas furnace and an A coil on top that has seen better days, what would I be best served to replace it with? I'd like to ditch the LP gas if it's economic to do so as something about gaseous fuel terrifies me, but short of installing an oil system in a place where I might have to fill the tank with offroad diesel given the dearth of fuel oil dealers I'm not sure if this would be wise. Electricity is about ten cents a kilowatt hour, roughly half the cost of power in Vermont. In 2020, is it cost effective to rip out an LP gas forced hot air system with AC and replace it with a heat pump and still be comfortable? Would it still need resistance heat strips to cover defrost cycles/really cold weather?

EBEBRATT-Ed

Probably a heat pump in that location. How about an LP furnace with a heat pump? You will have AC and can use the heat pump in mild weather (maybe all winter down there) and you would have the lp for a back up.

The difference in price between a furnace and a heat pump coil and an air handler with a heat pump coil is probably not that much

retiredguy

I would have to go with @EBEBRATT-ED's recommendation of a heat pump and a hot air furnace fueled with natural gas if available, LP or #2 fuel oil as back-up system. If you go with the fuel oil you can sink a 1000 gallon tank in the ground and have enough fuel to last all winter and then some. If you choose LP then you will probably have a large white tank somewhere in you yard. My fuel of choice would be the natural gas due to the least amount of maintenance and cleanliness, and probably the safest of the 3 fuels. Depending upon where you live, you might be able to have a wood burner outside with a hydronic coil set in the duct work of the indoor unit.

I live just north of Pittsburgh, Pa. and my last house had a heat pump system with an oil furnace back-up. (nat gas was not available) The heat pump carried the house load down to about 20 degrees F. and I could enjoy A/C in the hottest summer months. Back then I had my electricity delivered by West Penn Power for about 6 cents per KW.

HVACNUT

No matter which route you take, a controlled environment is key. Tighten the envelope, add a ducted whole house dehumidifier, a steam humidifier if needed, UV light or ionization generator, and a MERV 11 or better air filter without throwing off the SP curve.

Jamie Hall

I'd definitely go with a heat pump in that location and situation, and I think it could be made cost effective with the modern high efficiency units.

Do you have enough land to consider a ground source heat pump? More expensive, but can get to lower outdoor air temperatures since the heat source (the ground) is warmer.

I too would use LP, with a big buried tank, for your backup fuel -- and for your cooking (use a vented range hood!) and clothes drying -- and a generator big enough to run the whole show.

Also what @HVACNUT says.

ethicalpaul

Great suggestion, @Jamie Hall and I’ll just add that you don’t need a lot of land. You can drill a vertical well in as little space as a suburban driveway.

STEVEusaPA

I wouldn't put a 1000 gallon oil tank in the ground unless you use 2x that amount per year.
First, even with additives and stabilizers, today's modern, cleaner burning fuel does not sit and store well at all.
The generator company I do fueling for gets heavy use out of their fuel polisher.
More importantly, the regulations and compliance on underground oil tanks is very heavy, including the tanks must be registered (actually all tanks are required) and annual inspections (vapor/pressure) and submitted to the state.
And at some point that tank will have to come out. So unless you plan on installing it in the ground like they do at a gas station ($$,$$$), you're better off with a simple 275g Roth Tank, or a double walled steel tank and if outside, you could put a pump on it to fill your equipment.

BTW, off road diesel and heating oil are the same fuel. ULSD should be loaded with a lubricity additive at the refinery, bio doesn't need one. But they're both fine for off road diesel engines and oil burners.

Jamie Hall

Agreed -- a 1,000 gallon buried oil tank is not a good idea, for a whole host of reasons. I wouldn't do it unless I could bury it -- double walled with monitors -- like a gas station, and used a lot of oil, such as a big working farm might., A buried 1,000 gallon LP tank is another story altogether, and I'd still recommend it.

vtfarmer

Thanks everyone for your inputs! The property already has LP with I think a 500 gallon tank that also supplies fuel to the green house. The stove is gas but there is no smoke hood at all (island in kitchen with no hood above it, not a Jenn Air downdraft setup). CO and fuels that can leak scare me - I had propane in a house I owned many years ago and almost blew myself sky high once by hitting one of the burner knobs on the stove with my butt while shimmying around mopping and didn't notice it until the smell was pretty bad. I've dealt with LP salamander heaters and similar equipment over the years where I chased slow leaks down to find scratched mating surfaces in the flared fittings, leaky valves, and once I had an LP regulator start dumping gas out the vent port. I don't really want that on my home so LP is out.

I have an oil fired greenhouse heater I may bring from VT to heat the greenhouse at the new place with and will likely set it up to be supplied from a bulk tank I can use for offroad diesel (above ground skid mounted - would need to become permanent if the GH is attached). Getting that same tank connected to the house would not be feasible. I have a heat pump clothes dryer that I will be bringing with me - that is the coolest thing ever.

So I guess my question really is: if I have the LP furnace+AC system replaced with a modern air source heat pump, will it need any form or backup heat or are modern heat pumps able to deal with the winters the hills of western VA will see without issue? The property is a farm, so I have lots of land and I own a backhoe so trenching/burying lines for a ground source heat pump had crossed my mind, but those systems are more expensive to install and I want something that's cheap and simple.

Regarding wood, the house has two wood stoves which I intend to use (bringing my giant log-splitter with me), but that can't be the only backup if the heatpump is not sufficient by itself.

Jamie Hall

I'd have to research it a lot further, but I have a sort of gut feeling that, depending on exactly where you are in the hills of western Virginia, a ground source heat pump will be able to handle the job. You should check rather carefully the local (and I do mean local -- there are hills and hollows with weather quite different from down in the Shenandoah, for instance) to look into this further.

It may even be that an air source heat pump can handle the climate.

For most units, there is actually a fair amount of information available about what they can -- and cannot! -- do at low temperatures.

mattmia2

What about electric backup? Are you willing to mostly heat with wood during the extreme cold periods and use resistance heat when you can't deal with the wood?

ethicalpaul

Sorry to be a broken record but the best thing about ground source is the AC is absolutely fantastic. Nothing at all like an air-to-air compressor chugging in 100 degree heat trying to cool your house.

cheap I can’t talk about much here, but it was simple—I Bought and installed mine myself after hiring an engineer to spec it and a drill crew to sink the well and set the loop. And it needs less maintenance than an air unit 

anyway good luck with your project! You have a good shot at success regardless of technology with the smart research you are doing

HVACNUT

mattmia2 said:

What about electric backup? Are you willing to mostly heat with wood during the extreme cold periods and use resistance heat when you can't deal with the wood?

Exactly. But #vtfarmer needs to know the design day for his area, heating and cooling and research the manufacturers specs. A high efficiency 2 stage HP with electric backup might work out nice. Especially since rates are low (lucky dog).
And who makes that HP clothes dryer?

vtfarmer

The HP dryer we have is the Samsung model DV22N6800HW. It cost a bit to buy but saved me the headache of running a dryer vent from the small bathroom in the upstairs of the farm house that I converted into a laundry room. I was skeptical at first and it does require careful cleaning of the HX every 20 loads or so, but it works really well! It takes about two hours per load, so 2x longer than a normal dryer, but the capacity is adequate and it gets the clothes dry.

luketheplumber

I like to think of oil vs LP this way.
If the LP tank leaks and blows up that death will likely be instant and painless.
If you have a oil spill, you will in a very painful situation where you will wish you would be dead!

mattmia2

Oil also can cause a fire rather more easily than LP. LP is more dangerous than methane because it will collect in low areas, but if you use iron pipe and install things properly any leak you will have will be too small to be dangerous. The surface burner is really the only red herring here and that is because surface burners don't have to meet the same safety standards that even gas equipment of the 50's had to. I did something similar with my gas stove when working on something in my kitchen. I made sure I turned the gas off when working near it after that. You could also get one of the higher end ranges or cooktops with automatic ignition that will turn on the ignitor if it doesn't detect a flame.

TAG

I have used two Carrier 5 speed HP in two different houses ..I'm doing the same in my new build w/ a matching infinity propane furnace. The HP units have no problem giving full output down in single digits. With .10kw -- you are in propane cost area. In PA I'm at .20kw and NJ is higher .. so propane saves me a bit when it gets really cold. When my boiler went out a few years ago we had a 10 days of sub 10 degree weather and the unit never had a problem keeping the house warm. The new better HP's are silent

Steamhead

@vtfarmer , where exactly in western VA?

vtfarmer

@Steamhead Rockbridge County, outside of Lexington. The 99.6% design low is 12, Jamie Hall's comment about hills and hollows notwithstanding.

Erin Holohan Haskell

Good luck with the move, @vtfarmer. Should we change your username to vafarmer now?

vtfarmer

Erin, sure! If you can change a username that would be more accurate, except I will be the guy traipsing through my woods in Virginia looking for the odd maple to tap to boil syrup in the spring. That's much more Vermont-y than Virginia.

I have a question for The Wall: in an area with a 17 degree F heating design day, will these newfangled air to air heat pumps 1) work as advertised heating in colder temperatures and 2) make the house actually feel comfortable? I was all set to plan a geo-exchange heat pump replacement of the existing LP furnace+A/C coil then I found this (and similar units from other manufacturers):

https://iwae.com/shop/4-to-5-ton-18-seer-variable-speed-mrcool-universal-central-heat-pump-split-system-upflow-horizontal-ha20920.html?gclid=EAIaIQobChMI_tfoxtK_7AIVM_3jBx0VUwptEAQYASABEgKPePD_BwE

The literature says it will put out 100% of its heating capacity down to 14F, so in theory I wouldn't even need a backup heat source. The pre-charged line set with quick connect couplers is a bonus (anyone have experience with those?). The county has no problem with me installing something like this myself as long as I hire someone with a recovery machine to empty the existing A/C coil before I cut it out. I've done a first pass at a manual J for the house (~1800 square feet, built in the 90s, average weather-tightness) and one of these units in a 5 ton size would be sufficient (on paper) for heating and more than enough for cooling.

So what am I missing? Is the technology that this Mr Cool unit is representative of really up to the level where no backup heat source will be needed in my climate? Is that particular brand OK or would you all recommend another? I have exactly one firsthand data point in this area, and that's hanging around in southern New Jersey on a cold (high 20s - a cold day for that area) standing under a newer mini split while waiting for a piece of machinery to be repaired and marveling that the air flowing on my bald head actually felt hot. Hot like it was coming out of a proper heater, not just warm like I would expect from a heat pump with 28* ambient.

Thank you for the excellent free advice, as always!

Erin Holohan Haskell

vtfarmer said:

Erin, sure! If you can change a username that would be more accurate, except I will be the guy traipsing through my woods in Virginia looking for the odd maple to tap to boil syrup in the spring. That's much more Vermont-y than Virginia.

In that spirit, I'd say you should keep it vtfarmer. And I hope you find that maple.

vtfarmer

Happy 2021 everyone. Here's an update on my "when in Rome" quest for the current state of the art in heat pump technology as a cast iron radiator aficionado/air-conditioning hater who has transplanted to "The South". Here is where I've gotten so far: the local HVAC installers are very busy and hard to get to return calls, let alone come out and give an estimate for replacing an old LP furnace + AC system with a heat pump. The one contractor who did come look at it had "never heard of" a manual J calculation and is going to quote me some 1970s technology (conventional heat pump with resistance heater).

I did my own calculations with the NREL tool and came up with the following heating and cooling simulation

The spikes represent design days (if I read the instructions correctly) so I'm looking at ~60k BTU for heating and ~20k cooling. This is for a newer, well insulated 3780 square foot two story house that mostly shaded with the lower level partially underground (main level and finished basement) so these values seem reasonable to me (and I did meticulously plug my building's details into the NREL tool). The existing system is a 3 ton AC with 125k BTU 90% eff. hot air furnace. We had a design day around Christmas (15 degrees in the morning - balmy to me but you'd think the world was ending by how some of the people around here acted!) and the LP system cycled maybe a third-half of the time so that jives with my numbers.

Back the the new system selection: I described my heat loss calcs to the prospective installer and his reaction was something like "60k BTU?!? That's way too big! No way you need 5 tons..." which is correct, I don't need 5 tons of cooling but on a design day I do need about that in heat. I had assumed that with today's technology we would be able to get a heat pump with some kind of variable speed compressor/fans that could modulate up to my winter heating peak load and down to my average summer cooling load and be just happy doing that.

Regarding geoexchange, that's still an option but I see products like this and wonder whether that financially makes sense down here: https://lghvac.com/residential-light-commercial/product-type/?productTypeId=a2x44000003XQzG&iscommercial=false&class=Single Zone

mattmia2

There are modulating heat pumps. You have to dig in to the actual specs though since the capacity falls off with a decrease in outdoor temp, so if your design conditions are 15 f outside, you need to look in the tables in the specs and find something that will be 60 mbtu at 15 degrees outdoor temp, or add some sort of alternative backup.

vtfarmer

@mattmia2 yup, it looks like that LG unit and the ones similar to it will be pretty close with how cold it gets here at its coldest and just fine the vast majority of the time: