Replies

1. 
   MattJF | Mar 11, 2020 03:28pm | #1

   It is highly unlikely your cooling only load is anywhere close to 12Kbtu unless you have an entire wall of floor to ceiling south facing glass.

   What are your electric rates? It is very possible running a minisplit heat pump is more cost effective for all but the coldest days of the year. In New England it makes sense to size these systems primarily focusing on the heating load. You can follow the instructions here to estimate your heating load: https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

2. Expert Member
   Dana Dorsett | Mar 11, 2020 03:35pm | #2

   >"I have a Raised Ranch of about 1300 square feet with minimal attic insualtion and 14 years old double pane windows. "

   ----

   >"HVAC contractor said he performed a load calculation and 12K BTU would be enough, but said to be safe I can go for 15K. Since, I have Oil boiler as a main heat source, he said single zone Hyper Heat would not make sense which I kind of agreed."

   HVAC contractor load calculations are usually junk ( garbage-in=garbage out). The cooling load of a 1300' house with any low-E windows (which were code-min in most places 14 years ago) and R25 in the attic (half currrent code-min) would usually be less than 12,000 BTU/hr, which could even be delivered by the 3/4 ton FH09NA (or -NAH) at northeastern US outside design temps:

   http://meus1.mylinkdrive.com/files/MSZ-FH09NA_MUZ-FH09NAH_ProductDataSheet.pdf

   Take a look at this plot of square feet per ton against house size from a few dozen Manual-Js performed by Energy Vanguard in Decatur GA, and consider most of these houses were in the Gulf Coast states with higher 1% design temps and higher latent cooling loads than the northeast:

   https://beta.greenbuildingadvisor.com/app/uploads/sites/default/files/images/Bailes_graph_for_Manual_J_blog.preview.png

   The cluster of houses in the 1000-2000' range had an average area to load ratio of about 1200-1300 square feet per ton, and only the worse performing houses (probably R19 in the attic, single pane windows, no wall insulation) would need anything as big as an MSY or MSZ GL18, which can put out 22,000 BTU/hr even when it's 95F outside:

   http://meus1.mylinkdrive.com/files/MSZ-GL18NA-U1_MUZ-GL18NA-U1_ProductDataSheet.pdf

   http://meus1.mylinkdrive.com/files/MSY-GL18NA-U1-MUY-GL18NA-U1_ProductDataSheet.pdf

   The GL15 is good for over 18,000 BTU/hr @ 95F- in a 1300' house that would be 868 square feet per ton, which would only be appropriate for a WAY sub-code house in the northeast. (Do at least have some insulation in the walls?)

   http://meus1.mylinkdrive.com/files/MSZ-GL15NA-U1-MUZ-GL15NA-U1_ProductDataSheet.pdf

   Even though you have the oil burner, the COST of the heat from a hyper-heating ductless is dramatically less than an oil boiler even when it's a fairly cool 20-25F outside. Oil only wins the $/MMBTU game when it's...

   A: correctly sized for the load (which it isn't for a 1300' house unless you sleep with the windows open when it's 0F outside)

   ...or....

   B: an island location with extremely high diesel generator utility rates

   ...or...

   C: you have an oil well and refinery on the property and can get #2 oil at below wholesale pricing.

   So while it still makes more sense to size the unit for the actual cooling load, a hyper-heating model would also be able to provide half or more of the heat at a discount. While the MS_ GLxx units will also heat for less $/MMBTU than an oversized oil burner, they run out of capacity and efficiency at lower temps, and can have issues with destructive defrost ice build-up in the bottom pan of the outdoor unit if used extensively at subfreezing outdoor temps. At the very least going with the MSZ (heat pump, not cooling-only) version of any GL series unit would be worth the upcharge, even if staying away from hyper heating.

   Take a step back and run your own Manual-J-ish load numbers using freebie online tools such as CoolCalc. Be aggressive rather than conservative about air-tightness assumptions. LoadCalc is another that is sometimes useful for heating loads, but doesn't have a low-E selection option for windows, and will overstate the cooling loads. (It overstates heating loads too, but not by as much.)

   Since the ultimate goal is comfort, spending at least some money on fixing any low-hanging fruit like air sealing and attic insulation will do more for comfort than upsizing the cooling equipment by a half ton or more. Nate Adams' freebie download chapters and short videos are worth reviewing before selecting the equipment:

   http://www.natethehousewhisperer.com/home-comfort-101.html

   http://www.natethehousewhisperer.com/hvac-101.html

   http://www.natethehousewhisperer.com/hvac-102.html

   A room by room load calculation might give you a better idea of whether a mini-split in the main area would keep the bedrooms sufficiently cool. With the bedroom doors open the latent loads (humiidty) could all be taken care of, but a doored off bedroom at the end of the hall with a lot of unshaded west facing window might see a big solar gain late in the day big enough to want a window-shaker.

   BTW: To sanity check the Manual-J, run a fuel-use based load calculation on wintertime oil use. If the heating load output from the tool is significantly higher (more than 15% higher) than the fuel-use derived numbers, you're not being aggressive enough on the inputs. See:

   https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

3. Expert Member
   Akos | Mar 11, 2020 03:39pm | #3

   Unless your electricity costs are crazy high, a hyper heat unit will cost less to run than the oil burner. Even if you are only heating the main area of the house with it and using the boiler for the rest, the heat pump will be cheaper to run.

   In terms of the units size, since the living space is only part of your 1800sqft, I'm guess at most 1/2 that area, the 12k unit is more than enough. Although it is rated at 12k, the unit provides more cooling, it can do 13.6k.

   You can downsize even further, but there is very little difference in minimum capacity between the MUZ-FH12NA and MUZ-FH09NA and you get more heating during those near 0F days.

1. Expert Member
   Dana Dorsett | Mar 11, 2020 03:50pm | #4

   >"You can downsize even further, but there is very little difference in minimum capacity between the MUZ-FH12NA and MUZ-FH09NA and you get more heating during those near 0F days."

   In zone 6 it's better to go with the MUZ-FH12NAH or MUZ-FH09NAH (which come with a pan heater for clearing defrost ice.) The outputs are the same as the _ _ NA (non H) versions, heating efficiency modestly lower due to the power used by the pan heater

   A 1.25- 1.5 ton air conditioner is plain crazy for cooling just half of a 1300' house (that's 650 square feet). It will do it, but it will be less comfortable than something more appropriately sized. Even a half-ton FH06NAH (9000 BTU/hr cooling @ 95F, 8000 BTU/hr heating @ +5F_ would handle the likely cooling and heating loads of just half the house fairly well, but since the 3/4 ton FH09 has the same minimum-modulation numbers there isn't a comfort or efficiency gain from going with the half-tonner.

4. 
   ad060752 | Mar 11, 2020 04:23pm | #5

   Thanks All for your valuable answers.
   Basically, I have two concerns:

   1. Whole main floor is 1300 sq feet. Living room kitchen dining will be more like 750 or so. If I go with a bigger size say 15k or 18k, will the air go al the way to the bedrooms if doors left open? Throw capacity for 15k is 28 feet cooling, 34 feet heating where for 18k it is 39 feet cooling and 44 feet heating. The distance between the walls of two end of the house would be 47 feet. When contacted Mitshubishi, they said the unit is only designed to cool or heat one open area not multiple enclosed rooms.

   2. I understand hyper heating cost would be cheaper than oil. (Electricity Rate about 22 cents/kw). However, u have only one thermostat in the hallway for the while floor. In winter, I usually set 68 during day and 61 at night. If I use both heat pump and oil boiler, then will there be any savings? If I set the boiler thermostat at 62 all the time and set the heat pump at 68, then wint my bedrooms feel really cold?

   So, I guess my main issue is since I am going to install one wall unit at one end of the house, would enough air cross all 47 feet to the other end of the house to cove the bedrooms. Little delta is understandable.

   Pricing for
   12k Gl $4,150
   12k Fh $4,460

   15k Gl is $4,450
   15k Fh $4,750

   18k Gl $4 769
   18k Fh $5,050

   Appreciate your suggestionss

5. Expert Member
   Dana Dorsett | Mar 11, 2020 05:03pm | #6

   The 1-ton FH is $500 -1000 or more higher than it would cost in competitive bidding in my area. The typical cost is in the $3.5K/ton range give or take, all-in fully installed by professionals. Take a look at this page- in particular the pricing distribution graph in the lower right:

   https://www.masscec.com/cost-residential-air-source-heat-pumps

   About 75% of those are Mitsubishi, and the vast majority of the Mitsubishis installed are hyper-heating.

   Again, without the room by room load number it's hard to guess just how much colder the remote rooms might be. With the blower set to medium or high the FH09 or FH12 still has a substantial amount of throw. From a room to room temp point of view it's unlikely that the max 533 cfm of a GL15 is buying you anything appreciably more than the max 398 cfm of an FH12 or 381 cfm of an FH09. Bedrooms without a lot of window area (= bigger solar gains, bigger heat loss) can usually track reasonably well with the bedroom door open until it's below freezing.

   Many 1300' houses can be pretty comfortable even when it's 20 F outside with a wood stove or pellet stove in the common area, even without a blower. A mini-split set to somewhat overheat the main area can still deliver heat to the remote rooms, but buying a oversized mini-split with an oversized blower isn't going to heat the remote rooms any better, since it will be cycling on/off and deliver some wind-chill & noise when operating. A ducted mini-split in the basement might be the better whole house cooling & heating solution, but it'll be more than 5 grand (though shouldn't be more than ten in competitive bidding.)

   What is the BTU/hr (or gph) of your boiler?

   Got a ZIP code, and some wintertime fill-up dates & amounts?

   Most reasonably tight 1300' houses with double pane windows, some fluff in the walls & attic over a 1300' basement would have a heating load of about 25000 BTU/hr @ 0F if the basement walls aren't insulated, to about 20,000 BTU/hr @0F with an insulated basement. (Some raised ranches have insulated basements and reasonably air-tight insulated cantilevered first floors overhanging the foundation walls. Others have uninsulated basements and cantilevers that leak like sieves, but that can be fixed. )

   Without knowing your location it's hard to know if 0F is very near your 99% outside design temp, but it's probably within 15F of your outside design temp, but it's a stake in the ground to work from when the only location information is "North East region". Care to make a guess? See:

   https://higherlogicdownload.s3.amazonaws.com/ACCA/c6b38bda-2e04-4f93-bd51-7a80525ad936/UploadedImages/Outdoor-Design-Conditions-1.pdf

1. 
   ad060752 | Mar 11, 2020 06:05pm | #7

   Thanks Dana, when it comes to technical stuff, I am a Lehman. So, my understanding is what you are saying is whether I get 12k or 15k in the living room wall, the air will cross 47 feet to the bedrooms. Am I correct? It's the distance I am most concerned about.

   Could you please address my second concern about using hyper heat model as mentioned in my previous post...."if I run both boiler and heat pump simultaneously, won't it cost more? If I set boiler temp lower so it does not turn often, then won't the bedrooms be very cold? I usually set boiler thermostat at 68 daytime and 62 night time"
   BTW, I am in Connecticut new haven county coastal line zip code 06460.
   3 bedroom sizes are 11 by 13, 11 by 11, and 13 by 13.

   Not sure how big the boiler is (that's how Lehman I am). Been living in the house for less than 2 years. Average annual oil usage is about 660 gallons @ $2.45 / gallon.

   Really appreciate and thanks

6. 
   ad060752 | Mar 11, 2020 06:26pm | #8

   Attached the layout of my house. The area BAS SFB is the main level where the open concept living dining kitchen along with bedrooms and bathrooms.

   Thanks