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Help me determine steps to take to upgrade air sealing, insulation and hvac

aaron55 | Posted in General Questions on

Hi everyone!  I’m Aaron.  I’m SO glad I found this website!  I decided to look into getting Dandelion geothermal a month ago or so, and a little research has opened up a million questions about energy and HVAC that I have been trying to answer from air sealing to ASHP to GSHP to spray foam and on and on!  I hope you can guide me a little bit to help me achieve my goals:

Ideally I’d like to move away from using fossil fuels while ensuring I have better comfort in my home in the summer.  We’d like to have better more even dehumidification and cooling in summer.  Heating is working pretty well (feels kind of cold in January but hey, it’s January in an old house.).  We keep it pretty cool upstairs in winter, like probably 50s mostly actually.  

Some details on my house:
-zip code 12603
– ~1500-1600 sq ft, 9′ ceilings (basic 2-story square house with hip roof)
– attic is finished 800 sq ft with 1 dormer and 2 skylight windows – kneewall around inside and old 70s or 80s fiberglass batts with plastic over it on rafters and then sheetrock on top of that.   – we will only ever use it for storage as the first two floors are more than big enough for living space.  Floor is wide planks with some loose old grey cellulose (?) insulation in joist bays, carpet is on top of the planks but can be rolled away easily to insulate better if needed, or just get rid of it either way.
– Basement is stone foundation that transitions to brick and about half of it is above ground.   -not really any insulation other than one side has some fiberglass batt stuffed along the rim joist.
-no wall insulation in most of house other than some fiberglass batts put into small kitchen’s walls when we renovated a couple years ago. 
-original wood cladding siding
-lots of big old windows in house – original single pane glass – not too drafty due to some caulking and fixing I’ve done as well as use of mortite rope around sashes to reduce drafts.  Really old aluminum storms on first floor that are quite terrible but are there.  Newer painted aluminum storms on second floor that are better but also mediocre.
-96.5% efficiency forced air natural gas furnace installed to replace gravity furnace (!) in about 2009. (original supply ducts run to 4 bedrooms in second floor, bathroom on second floor and into dining room, living room and kitchen on first floor.  No returns on second floor and returns in foyer, living room, dining room and under central staircase first step.) 
-furnace is set for M-F 5PM-10PM 65F, 10PM-5PM 58F; Sat Sun increase furnace from 7-10PM to 65F.  thermostat is in dining room; upstairs cooler than downstairs due to wood stove downstairs.
-we use a Jotul Oslo M-F from 5-11PM and more on weekends – it is right in our living room and provides comfort all winter as we spend most of our time in the living room
-no air conditioning other than portable unit used occasionally in our bedroom.  
-only 2 of us in house (and a dog!) and will only be 2 of us for probably the next 20-25 years other than a few guests infrequently visiting.
-I hope I didn’t bore you too much lol!

Through deep-diving into this exploration of HVAC and insulation and such I think I could benefit from some upgrades but wanted to run it by you all.  I especially thought this would be wise before figuring out the HVAC and sizing and all as many have suggested. 

I thought maybe putting in spray foam in my attic floor or maybe the rafters (if I tear out the old sheetrock and old  fiberglass batt) would be a good investment.  Since we don’t use the attic for living space, the floor maybe makes more sense?  The only issue there is I guess I’d have to tear up the carpet and a bunch of floor boards and then clean out all of the old cellulose before they inject the spray foam into all of the joist bays?  Not sure what makes sense.  I know there is a good air path straight up the outside walls to the attic, so it seems to make sense to seal up that better if possible, maybe do the floor and up the rafters a few feet?

I hope to also have another blower door test done and some air sealing on the 1st and 2nd floors to find any really bad places for air leakage.  I had a door test done a few yrs ago and it was around 2650.  i think that was with the attic door closed.  when attic door was open there was enough inflow of air to pull of the door to the knee wall storage space!

Finally, I will likely have the rim joist spray foamed since everyone recommends that it seems. Does it make sense to insulate the above-ground portions of the walls as well to try to keep the basement a little warmer?  the basement is in the mid 40s when it is in the teens or single digits outside currently.

Regarding the HVAC component:
So, I talked to Dandelion because I thought geothermal would be awesome and the best.  Then, I started looking into mini splits and multizone ASHPs  and I’m all confused.

Dandelion originally said they would require us to put in a return on the second floor.  So, I had a guy come out and he said he wanted to redo all of my ducts, using 1st floor supplies (all supplies in house are on non-perimeter walls) as returns instead and installing supplies around the perimeter of the first floor in the floor.  Second floor, he wants to convert my old original supplies upstairs into returns and then put in several supplies in the ceiling around the perimeter of the ceilings in all of the bedrooms.  Supplies would run through the attic kneewall space with R6 insulation.  That estimate was $16k.  We had also discussed just putting in a return to each bedroom  through the ceiling and run through the attic and down to the basement through a chase.   He didn’t quote that but I asked him to.

Then, Dandelion said they no longer would require a return on the second floor since it’s an old house and it’s not ideal and we could add it later if it doesn’t work as well as we want with no returns upstairs (for cooling season.). Dandelion’s final cost after all rebates and tax credits is going to be $23k to install a 2-stage 6T GSHP.  

I haven’t gotten a quote for ASHP yet.  I thought the GSHP would be better since it should last twice as long, has no components outside the house, makes no noise outside, etc.  But, then I started wondering if it would be crazy to just try at least one ASHP out and keep the gas furnace for now?   Part of my thinking on this is that I did the estimate of heating load using Dana’s method where you calc. gas usage over January, etc.  I got a heat load of only around 17.8-19.2k btu/h at 60F doing that!  I guess it’s b/c we use the wood stove so much and keep our thermostat so low most of the time?

Would it make sense to do the air sealing and insulating that is recommended (maybe make some wooden storm windows that I can seal against the outside window frames as I have time over the next few years as well) and then just try putting a 18k btu ASHP in our living room to see how it does?  The floor plan is sort of open with living room in front corner of house, two double-wide doors out of it, one to foyer and one to dining room and then kitchen in opposite corner with a couple doorways into it.  I figure it might heat our first floor adequately, especially with the wood stove.  If not, I’ve got the gas furnace as backup for now.  It should be more than adequate to cool the first floor and dehumidify in summer.  Then, I just don’t know what to do about the second floor.  I thought maybe putting in a 9k btu unit into our bedroom and one into one of the other bedrooms.  We can leave all of our bedrooms open most of the year, just when guests come over (rarely) would we need to close the doors.

I don’t know if a Manual J is as applicable to us since we are just 2 people in a big old house and we’re not super picky about heating every space perfectly.  I’d like more cooling comfort in summer and dehumidification though.  But that needn’t be super even either.  Mainly I want the living room best followed by dining and kitchen.  Upstairs cool is ok in winter but would like it more comfy in summer.  We have ceiling fans in all of our bedroom as well which i thought might help with cooling if we had just a couple splits upstairs?  

Thanks for any suggestions!

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  1. paul_wiedefeld | | #1

    Geothermal is a terrible fit for this application since you have an existing furnace and lean on wood as it is. An easy solution would be adding a heat pump to the existing ductwork in a hybrid set up. That might get you 80% of the emissions reduction for 20% of the geothermal cost, depending on ductwork modifications.

    A 6T geothermal system? That’s gigantic. How much gas and wood did you use last year?

  2. aaron55 | | #2

    Thanks for your thoughts, Paul! I don't know why I didn't think to try to estimate my wood usage and combine it with my gas to estimate my total heating load! thanks!

    Anyway, I am estimating I use maybe 4 cords per year of locust, oak, maple and some crappier stuff, so call it 24M btus/cord. That is around 100M BTUs per year, which is about 1000 therms-worth and the stove is maybe 65% efficient? Holy ----! I didn't know I was getting that much heat from wood, 650 therms-worth?!

    My gas usage is around 400-450 therms per year, of which about 100 are the hot water heater (8 therms used per mo. in summer.). So, that's maybe 300-400 (350 avg) therms of gas devoted to heating the house per year.

    So I'm using around 1000 therms-worth of energy total to heat my house for a year as an estimate. If my calculation of heat load for last Dec 20th - Jan 20th using Dana's method gave around 19k BTU/hr with gas alone, then my wood calc would come out to 38k BTU/hr right? That's 57k BTU/hr. Does that make sense? My wood estimate might be a little high there, so it could be like 50k BTU/hr maybe. Does 4T sound more realistic for a sizing for my house for heating?

    My current ducts are not great. The returns are very leaky and run in the joist spaces in the basement ceiling. The supplies are old and original and probably leaky. Maybe these are not that important considerations though in my case? I am a bit worried about condensation forming on the ducts in my basement if they aren't sealed up and insulated. That is why I thought a mini split might be better for cooling in my case. I guess I could have a few mini splits for cooling in the summer?

    Would a hybrid system basically allow me to use the heat pump most of the year but fall back on the gas furnace only when it's really cold out, or if I want a hotter temperature, or if I'm not using my wood stove for awhile? Also, i wanted to add cooling. I don't know if it would work to cool the upstairs when there are no returns?

    1. paul_wiedefeld | | #3

      Yes, a hybrid uses the gas for backup. Mini splits are usually used to describe ductless heads (often mounted high on walls) but that’s no longer accurate- they can be ducted as well in high, medium or low static situations. An installer should help you mix and match the right heat pumps for your situation. Maybe ducted with new ducts in the basement (easy to replace) for the first floor then a ductless upstairs or maybe a smaller ducted unit upstairs. Having a single ductless head in a bedroom is usually suboptimal as the ones small enough to not short cycle while cooling are also too small for dehumidifying, but combining multiple rooms can get around that.

  3. aaron55 | | #4

    awesome! Thanks for the input. Those might be some good options.

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