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Best heating system?

I want to install a secondary heating system (wood stove primary). Cold climate. What is best ductless heat pump for an open house plan, 2-story?
Are heat pumps better than ETS systems?



Asked by Kelly Mitchell
Posted Aug 16, 2014 12:56 PM ET
Edited Aug 18, 2014 6:50 AM ET


8 Answers

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There are lots of articles here on the topic of ductless minsplit heat pumps: http://www.greenbuildingadvisor.com/blogs/dept/musings/heating-tight-wel...

In order to evaluate the cost of running an ETS system vs. a minisplit heat pump, you must know what your off-peak electric utility rate is. http://www.steffes.com/off-peak-heating/save-money.html

Xcel Energy in Colorado, for example, has abandoned the off-peak rates that were in place since the 1970s. http://greenbuildingindenver.blogspot.com/2008/10/what-ever-happened-to-...

Answered by Kevin Dickson, MSME
Posted Aug 16, 2014 2:31 PM ET


If you live in a cold climate, and you want to install a ductless minisplit, you'll probably want to specify either a Mitsubishi or Fujitsu unit.

If you can find a local contractor who can install and service the equipment, choose the brand (Mitsubishi or Fujitsu) that the local contractor supports.

Answered by Martin Holladay
Posted Aug 18, 2014 5:34 AM ET


I don’t get it. Are you using an external or internal wood furnace? Forced air distribution of conduction/convection distribution? Auto fill or manual fill of the firebox?

How can a heat pump be a viable secondary heating system in a Zone 5 or colder climate?


Heat pumps are not efficient in cold weather which is when the secondary is used as an emergency backup and or as a supplementary (i.e. cold mornings before the wood stove is cranked into action).

If you are used to an indoor's wood stove or furnace primary, you will be p'ed off when you turn on the minisplit on a Zones 5 or 6 cold morning and wonder if you accidently turned on the air conditioner.

Seems to me that electrical resistance space heating (direct or indirect, air or conduction) would be faster and stronger. And since its not much in use, the operating cost will be tolerable, as the wood furnace caries most of the load anyway.

Answered by flitch plate
Posted Aug 18, 2014 12:50 PM ET


Q. "How can a heat pump be a viable secondary heating system in a Zone 5 or colder climate?"

A. Heat pumps are now available with significant heat output at below-zero temperatures. For example, the Mitsubishi Mr. Slim Hyper-heat model number PUZHA36NHA is rated at an output of 30,000 Btuh when the outdoor temperature is -13 degrees F.

Answered by Martin Holladay
Posted Aug 18, 2014 1:30 PM ET


If you look at the submittal sheets on the Mitsubishi cold-climate mini-splits you'll see a note with a double-asterisk pointing out that they are designed to turn off when the outdoor temp drops below -18F, and will automatically re-start when it warms up to -13F. While this is not a problem for most of US climate zones 5 & 6, it will be a problem for many climate zone 7 locations.

http://www.mehvac.com/media/953333/msz-fh15na_muz-fh15na_submittal.pdf ( See the bottom of page 2.)

Internet scuttlebutt has it that they will in fact keep running into the -20s F, and speculation is that -18F is probably the warmest temp at which it will auto-stop. But it's worth paying attention if your location regularly drops south of -20F.

The -FHxxNA Mitsubishi mini-splits still operate with a COP of about 1.8 while running at full speed at -13F, and if modulating at part load will be north of 2.0 even at that low temp. The part-load efficiency at +17F is north of 3.0. Most US climate zone 6 locations will have binned hourly mean temperatures in the +15F range, and you could expect them to have seasonal average efficiencies of 3 or better if properly sized for the loads. (Even under-sized units in a group of 12 field-monitored by the NEEA in Idaho Falls area averaged about 3.0, and that was the older -FE12NA, not the FH series, which is ~15% more efficient than the FE series under HSPF test conditions.)

The Mitsubishi FH-series mini-splits test at higher efficiency than the Fujitsu cold climate xxRLS2-H series, not that the latter are bad by any means. The -H series also tests at a lower efficiency than their direct ancestor & sibling xxRLS2 (no -H), probably a function of the pan heater they added for defrost water management. (That feels like a bit of a band-aid of a solution in the first place, but maybe it's necessary in some climates.) The Fujitsu units do not have that auto-stop feature/problem that the Mitsubishi units have, and are probably a better solution for colder zone-7 climates.

Answered by Dana Dorsett
Posted Aug 18, 2014 2:18 PM ET


Looks impressive (but pricy):

75% efficiency at -13F. 100% at +5F. $5000 to $7000/unit (not including line set)



But what about payback. If its not mortgaged, its a big outlay when I can get 30,000 BTU's for less than $600/unit in an exterior vented, electrical resistence forced air heat distribution furnace.


or a Broan-Newtone with ECM motor for $1500 - $2500


Answered by flitch plate
Posted Aug 18, 2014 2:19 PM ET


Flitch Plate: That's 75% of nominal CAPACITY, not it's efficiency. The efficiency of ANY of the H2i ductless systems is more than 100% @ -13F.

The FH-series mini-splits will still hit 180% or higher efficiency, @ -13F. But their capacity at that temp will be ~65-80% of it's nominal +5F capacity at that temp. Installed cost is about $4000/ton.

Without knowing the actual heating load and outside design temperatures you can't really specify the system that would be called for, let alone estimate it's cost.

If used only as an auxilliary system the upfront costs of ductless heat pumps isn't necessarily justifiable. In my US zone 5 location where electricity costs 16-17 cents/kwh, the marginal cost of heating with mini-splits is comparable to or less than heating with $250/cord hardwood (the typical delivered cost per cord) in an ~80% efficiency wood stove, and a heluva lot more convenient.

Electric baseboards, cove heaters or panel radiators make a lot more sense than electric furnaces for auxilliary only backup, since they are inherently micro-zoned, and don't increase infiltration rates the way ducted hot air delivery does.

Answered by Dana Dorsett
Posted Aug 18, 2014 4:18 PM ET


There you have it, Kelly. Depends on a lot of info you have not provided: like what is your system now? Forced air, radiant/convection, or hydronic distribution of wood heat?

Local electrical costs and of course the buy-in capital costs and rate of return may be the decisive factor.

For a backup secondary, space heating with radiant seems to make the most sense. I don’t like a forced air atmosphere even if it’s over 100% efficient. And Dana’s point to increasing infiltration with forced air means reduced efficiency that way as well.

I am curious, why would you consider electric thermal? If you’re already built, how to you propose to add in the mass storage component ?

Your solutions seem more like adding another primary system than a supplemental or backup solution.

Answered by flitch plate
Posted Aug 19, 2014 7:52 AM ET

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