I'm considering making an offer on a home just outside of Boston, MA. Alas, the home was built in 1981, and thanks to the energy problems of the day, it was made 100% electric. The home is about 4600 sqft. The Kwh usage of this home during the worst winter months can be close to 10,000 Kwh! That equates to as high as $2200/month at early 2015 pricing. That, to put it mildly, is not doable. The home is mostly electric baseboard heated. It has 5 Fujitsu mini-split systems, but I believe they're older models (2010 - confirming soon) that don't operate well below freezing, so they probably rely a lot of the electric resistance heating. Even if they relied entirely on the mini-splits, only about 45% of the home is "covered" by the mini-splits. The current owner did some re-insulation during a 2010 renovation, but the details are scant. (I think they're a bit defensive about the utility bills, to be honest. They're in denial.) Some windows are single-pane, but most are pretty good double pane (circa 2010) windows. To make matters worse, there is no basement. It's built directly on a slab which is on top of a rock ledge. I'm not sure if the slab has a crawl space - again, confirming soon. Regardless, converting to oil or propane heat would be difficult due to the lack of basement, lack of ducting, and lack of piping. We love this home, but unless we have a plan for *massive* reduction in electrical usage, it's a no-go. My current "plan" is to replace the existing mini-splits with Fujitsu RLS3h, and add 4 more. This should get my coverage closer to 75% (just not in hallways and bathrooms), but at a cost of probably $25k. I'm also hoping to add insulation to the foundation that's exposed to the air, which I've read can save 10%-20% on heating costs. Lastly, adding a massive solar array (19Kw) at a cost of $75k before incentives (about $55k after) should reduce my grid consumption by another 30-40%. So that's about $100k, and I'm not even sure it's going to work. Any advice would be greatly appreciated.

You'd have to start with an energy audit (preferably an independent audit - with you present - to see where the problems lie. Then plan for added insulation which could be pricey since it might need to be on the exterior. You CAN get this house down to a reasonable cost to condition, but it may take $$$. Maybe the seller will take a low offer since he might have issues selling?

Will getting this under control cost less than $100k?

The nice thing about the solar panels is that, even if we don't reduce the usage, they have a known ROI of about 30% in the first 10 years with a payback period of only 6 years thanks to the incentive programs in MA.

In Massachusetts there are huge subsidies available for air-sealing and insulation (like 75% of the cost!), even window replacements in some cases if they're crummy enough (and you ask nicely.) Start by going to MassSave.com and seeing what's cookin' in your ZIP code, and schedule an audit.

There are also rebate subsidies for mini-split heat pumps, provided they meet the efficiency specs, which use less than 1/3 of the power per BTU delivered compared to baseboards. A co-worker of mine installed 3 mini-splits in his Arlington digs this summer to the tune of about $12K up front, but with the Mass CEC and other rebates the total out of pocket was about $9500. YMMV. (We ran the heat load calcs ourselves, to weed out the truly insane proposals, of which there were several.)

The marginal cost of heating with oil or propane is more expensive than heating with mini-splits even at this past winter's insanely high electricity prices, and the new-improved lower price for oil.

The Fujitsu RLS2 series are pretty efficient compared to most even at sub-zero temps. (HSPFs in the 11s and 12s) There's no "payback" in replacing them with RLS3s (HSPF in the 14s) within the lifecycle of the equipment. If they are some other series, what are the model numbers?

It's also insane for any house to have 5 mini-splits, let alone (5+5=) 9. The min-modulated output at 47F for any of the RLS2s or RLS3 is 3100 BTU/hr which is more than the heat load of an individual room at that temp. Oversizing it too much leads to lower comfort from on/off cycling during cool outdoor temps, with wild swings in temp. You may be better off installing some mini-ducted units in the tops of closets or making some ceiling soffits to share the output between 2-4 rooms. The Fujitsu RLFCD mini-duct series are good down to -5F , just like the RLS2s, with HSPFs in the 11s, and have flexible mounting orientation, and have WAY better air-handler drive than the competition.

To get the best efficiency out of mini-splits you "set and forget" the temperature setpoint and let it modulate. But if you have 3/4 ton ductless heat in a room with a design heat load of 4000 BTU/hr @ +10F (or whatever the outside design temp is in your zip code), it almost never modulates, which cuts into both efficiency and comfort due to the on/off cycling. Even the 3/4 ton Mitsubishi FH09NA which modulates down to 1700 BTU/hr @ 47F would be cycling most of the season. It's a great mini-split when appropriately applied but it's almost always going to be too big to be optimal for a single ~150-200' bedroom with a 3000 BTU/hr design load. (With a design load that small the Fujitsu 9RLS3 would literally never modulate.)

So, when the time comes, do a room-by-room heat load calculation (I=B=R methods are fine for sizing mini-splits) and don't oversize them by more than 1.5x for capacity at your 99% outside design temp. You'll have to look up what that 99% temperature bin is, and you'll have to consult the extended temp capacity tables if it's below +17F (which it is, in suburban Boston) for most mini-splits.

And, since you'll be doing some window, air-sealing and insulation upgrades, run the heat load numbers on the AFTER picture, not the as-is-where-is condition.

You can probably gain a lot just by setting the thermostats for the electric baseboard heat to a good 5 F below the setpoint on the minisplits. That will mean that the electric baseboard will only kick in if it's really needed. It may doing a lot more of the work than it needs to, even before you make improvements.

Note that when you improve the envelope, you not only reduce the load, but you also make the temperature through the house more uniform, so heating with fewer sources becomes more viable, without hot and cold spots.

I think one problem (regardless of the models of the current mini-splits) is that they largely can't cover most of the home's square footage. The home has many rooms, and really only two of the five mini-splits are in larger, open areas.

I've marked the location of the mini-splits on the home's floor plans. Here is a link to them: https://onedrive.live.com/redir?resid=240479C9F819629E!95857&authkey=!ABOaYGYTEKTGYWk&ithint=folder%2c

As you can see, 3 of the 5 mini-splits are "trapped" in bedrooms, leaving about 55-60% of the home to be heated entirely by baseboards.

The heat load of that doored off office with it's own mini-split is probably less than 5000 BTU/hr @ +10F (or would be, with some tightening and window upgrading), and having it's own head is a waste. Depending on how you intend to use those spaces, relocating it to the family room or foyer would likely work just fine, but you may need to crank up the temp or leave the doors open to the office to stay comfortable in there during the colder weather. It The heat load of that 17'x 17' bedroom is probably less than 4500 BTU/hr @ +10F, and pretty marginal for a mini-split with a 3100BTU/hr mininimum @ 47F.

There are ample closet & utility room locations on the second floor that would be suitable for mounting a mini-duct cassette serving 2-3 rooms.

Bumping the ductless mini-split setpoints to 74-75F and just leaving it there to passively heat some of the adjacent spaces is cheaper than just letting the baseboards keep up. Using set-backs on the rooms where you actually have to use the baseboards can be worth it.

Once you fix all the air leaks and those garantuan single-pane glass heat leaks the room temps will start to even up considerably. On a high-R home you can typically heat 1000-1200' of conditioned space with an optimally located ductless head, but you may have to leave some doors open when the temps drop below +15F. With a 2x4 /R13 house with U0.35 windows that shrinks a bit, but it's ridiculous to have a dedicated ductless head serving 250-300 square foot rooms like that.

There might be a case for as many as 5 heads if it's ductless only (placed differently than currently) but 9 would be a waste. Two mini-duct cassettes could serve the entire second floor with better distribution comfort and efficiency than the pair of ductless heads up there. If you really felt you needed to keep the unit in the downstairs office, re-commissioning one of the upstairs units moving it downstairs if the balance isn't working out (and keeping the other one for spares) may be a better option than just throwing ever more ductless heads at the problem. The only thing adding four more ductless heads would be good for is perhaps making the installer's boat payments. (Good for them, not you.)

Figuring out the envelope upgrades in conjunction with room-by-room heat load calculations will be the necessary guide to narrowing it down any further. It's pathetic that they spent all the money on mini-splits rather than lowering the loads with building improvements. Any single pane window in a MA climate is a comfort problem even if electricity was free and you kept the place at 75F with baseboards.

Excellent advice. Apparently, there is another offer on the home. (Figures - place was on the market 500 days, we see it, and it has another offer 3 days later...arg....). I'd only be willing to take this risk if we can get a good deal, and with another offer in place, that's unlikely. Sigh.

Thanks for everybody's help.

You should be glad...what a mess!!! You would have been stressing about this for years and years.

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First you have to consider your fuel options.

I owned and all-electric house in Ohio a couple decades ago. I designed a radiant sub-floor hydronic heating system added a sealed combustion condensing boiler, indirect-fired water heater and installed a high velocity Unico systems for cooling.

I have designed many electric to gas conversions starting in 1987. The cost of operation is often a third of the original. If you are not concerned about winter comfort some form of mini-split heat pump may be in order.

Solar and ground-source heat pumps are usually expensive options with long ROI and payback where modest residential homes are concerned.