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Community and Q&A

Choose between more/better insulation, or heat pump?…

Soundview75 | Posted in Energy Efficiency and Durability on

Last year we had an energy assessment performed in our 1880’s home and were recommended several options. We opted to first pursue air sealing in attic with 20″ of blown in cellulose. This made quite a difference both in comfort and heating bills.

Our remaining recommendations:

1 – Insulate walls with dense pack blown in cellulose.
2 – Insulate crawlspace (closed cell spray foam).
3 – Replace 4 windows original to house (drafty!!)
4 – Install high efficiency air source heat pump.

Unfortunately, only enough budget for 1 of the 4 options (all estimates within $200-$300 of each other). According to energy assessment, our 10 year old furnace is fairly efficient and heat pump would strictly be to supplement and “even” out low winter temps. We also supplement with a wood stove.

Does it make more sense to invest in insulation or heat pump?

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  1. user-2575529 | | #1

    I would recommend improve the envelope first before trying to fix the comfort issue through mechanicals. Air sealing and insulating the attic is a great first step. Anything that you can do to lower the heat loss will help you to reduce the size of the mechanical equipment needed to heat the home in the future.

    You mention 4 original windows. If they are original then that would mean single pane glass. You can check if its single pane glass by putting a finger on each side of the window and trying to touch your fingers together. If it appears like they are touching then it is single pane glass, if there is a gap between your fingertips then you probably just have an old double pane window. Either way maybe a less expensive fix for the windows is to make some removable interior storm windows. Its an easy enough DIY project. Do a google search for "interior storm windows" and you should find some instructions. There are companies that make these as well, just trying to save you some money though.

    I would suggest that the next step is to insulate the crawl space. You should see more comfort from doing that then insulating the walls at this time.

    Hopefully you can make some simple interior storm windows and afford to have the crawl space sealed. Probably best bang for your buck at this point in my opinion.

  2. GBA Editor
    Martin Holladay | | #2

    If your energy auditor listed the recommended measures in the usual order -- starting with the "biggest bang for your buck" measure and then listing other measures from the most cost-effective to the least cost-effective -- then I would address the measures in the order they were listed.

    I would vote for insulating the above-grade walls or sealing and insulating the crawl space. Window replacement rarely makes sense, although it would probably be a good idea to install storm windows to protect any windows with single glazing.

    You can always install a heat pump later if you decide you want one. (By the way, you didn't mention the fuel used for your furnace. If it's natural gas, the heat pump won't save you any money. If it's propane or oil, then the heat pump will save you money. But if you have a wood stove, use the wood stove to lower your fuel bills.)

  3. Soundview75 | | #3

    Gentlemen, thanks for the considered responses.

    Both suggestions for tackling crawlspace insulation first are in line with energy assessor's recommendations. I only started considering heat pump recently after several coworkers installed in their homes to amazing reviews. But their homes were built in late 1980's and not 1880's. I'm sure their homes are significantly better sealed and insulated.

    (Btw, the 4 windows are single pane and I normally use window shrink film in the winter. This works well and is fairly inexpensive. But I'll definitely be looking into interior storm windows! And the furnace is oil fired, and, most certainly a guzzler!)

    Thanks again!!

  4. Expert Member
    Dana Dorsett | | #4

    Cheaper than a replacement window and better than shrink film, if the windows aren't all rotting & falling apart needing replacement no matter what, you can weatherstrip the windows and install low-E exterior storm windows. A good low-E storm over a wood-sashed reasonably tight single-pane performs at about U0.30-U0.33, as good or better than cheap replacement windows.

    The tightest storm windows in the industry are manufactured by Harvey (a northeastern US regional player), and they have a hard-coat low-E glazing option.

    The most widely available would be Larson, who distribute through the box store chains. Pass over their bottom-of-the-line "Bronze" series- they leak too much air- it's worth the upcharge for the Silver or Gold series, which are pretty tight.

    The quality of the clear grain old growth wood in 1880 vintage sashes & frames is unmatched by modern windows. If they're salvagable, it's worth tightening them up. Putting the storm window on the exterior keeps them warmer/drier and extends the life of the original window. If they are built with pulleys & sash weight pockets you can usually yard out the weights and replace them with spring coil units, and insulate the pocket, or, if you'd rather keep the weight & pulleys you can use lightweigt PVC as a weight-sleeve and insulate around it. It's sometimes advisable to leave a 1/4" air gap between your insulation and the exterior board, especially if the roof overhangs are shallow (= higher chance of bulk wetting), and there is no window flashing (common, old uninsulated houses.)

  5. Expert Member
    Dana Dorsett | | #5

    BTW: What fuel does your furnace use?

  6. charlie_sullivan | | #6

    If you might eventually have the budget to do all of these, doing the envelope first means that the size of the heating system can be smaller, saving you money when you get to that. Investing in a better heating system first often means you paid for a bigger system than needed. If your heat pump would only be supplemental, that rule might not apply in your case.

  7. Soundview75 | | #7

    Dana, it's an oil furnace. And great info about storm windows. Another option to explore. Thank you.

    Charlie, you make a great point and it's something I've been concerned about. I've had 3 heat pump contractors come out to provide estimates and only one bothered to grab measurements and ask questions. The other 2 simply walked through the house and immediately recommended their top of the line offerings. Not sure if measuring and asking questions is standard but I guess I was expecting more involvement from the other contractors in determining appropriate size of unit...

  8. wjrobinson | | #8

    Dana, what's your take on interior storm windows? I have a neighbor with 1980's picture windows, double pane. and there is a perfect spot on the inside for a low E storm to be added. South side of home but needed for winter heat season.

  9. Expert Member
    Dana Dorsett | | #9

    Christian: The cost of operation of an 87% efficiency oil furnace at the recent 5- year average fuel & electricity costs is more than 50% higher than that of a pretty-good high efficiency ducted heat pump and more than 2x the cost of running ductless heat pumps. Even though the cost of oil looks like it will be lower this year than the running 5 year average, and electricity might be rising, the fundamentals in both markets still favors heat pumps on lifecycle operation cost.

    If the floor plan is open enough that a large zone can be heated with a ductless heat pump, it would likely pay for itself in reduced oil use in under 5 years.

    AJ: Interior low-E storms on clear-glass picture windows can work. (IIRC Larson also does low-E interior storms, but I don't know if the box stores deal with 'em.) In some instances with a low-E interior storm the somewhat higher temperature difference between outside temp and air-space between the storm & sealed glass can stress the seals causing them to leak, but that isn't super-common in the north east..

    If the seal leaks the performance of the window doesn't change much- the hit from a broken seal & venting what had been a dry-nitrogen/air filled window is negligible (an argon filled window the performance loss is a bit higher). But when not-so-dry air gets in it can fog up inside the sealed glazing unit. in that instance the fogging can be mitigated nearly 100% by carefully diamond-drilling a few small holes in the exterior pane, venting it to the exterior. That way the air inside the glazing unit tracks humidity level of the exterior air. It's similar to the venting accommodations found in most exterior storms.

  10. KeithH | | #10


    I swear I don't have an interest in this site but here goes again. You might check out This is a very simple Manual J calculator. You can play with it quickly and see what effect on the whole house load some different options have. It's just a model but a model is better than what the window or hvac sales guy has to say. You can try out different windows or different building tightness ratings. It won't help you with the furnace upgrade projections but could help with windows or insulation upgrades.

    I have a couple experiential comments to offer as a homeowner and DIYer. We put new windows in our previous residence. More than a change in the heating bill (zero visible effect), the windows quieted the house compared to the old aluminum frames, reduced infiltration (and thus 'draftiness'). and didn't feel as cold to be near. These creature comforts were worth the money but I don't believe they save much money. I put our old residence through this software and concluded that converting all the windows and two sliders would lower the load a 3/4 ton or about 16%. We didn't see that on the bill however.

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