I've got a single zone forced air 120,000 propane furnace plus A/C.  Furnace is original (1992), A/C was added by the previous owner in the late 90's.  The standing pilot on the furnace has been a recurring problem over the past few years---multiple thermocouple changes and attempts to fiddle with it later I still have problems keeping it lit.  So I have three basic options:

1. Go the next stage with the existing furnace (probably new main valve, in the $500-800 range is my guess).
2. Upgrade to a 95% propane furnace, likely in the $5K range installed.
3. Go geo.

Last year I got a split quote of low $20's for a 3 ton geo plus new propane furnace to supplement, or around $30K for a 6 ton geo.  This includes the drilling, and upgrading the ducting for two zones and the additional air handling required by a heat pump.  I haven't gotten around to getting a fresh set of quotes, but I'm guessing those are low but in the ballpark.

House is a standard two-story Colonial in Southern NH.  Approx 2200 sq-ft plus 600 sq-ft finished in the basement.  There is a 13x18 bonus room with pitched ceiling, fireplace and skylight.  Very tight storm windows everywhere.

I had an energy assessment done, which showed problems mostly in the attic, both leakage and insulation.  Problem is that I had a drop-down stair installed, then sub-flooring.  This compressed the crappy blown-in fiberglass, and it turns out the joists are only 6".  Fixing the attic is an open question for sure, and is on the near-to-mid-term list.

I used HVAC Calc to estimate load, and arrived at 23-25K heat gain and 51-56K heat loss, depending on how pessimistic you get with the R-factor of the attic.

So does the 3-ton with supplement or 6-ton standalone sound right?

After I put one in, what's the maintenance overhead of the heat pump compared to fossil?  Service contracts/cleanings for the AC and furnace are easily several hundred a year.  How about life expectancy?  If I go 6 ton, should I be considering dual-stage and/or strip heat?

What's the risk of a major surprise when drilling the Big Hole?

The airflow design in the house is pretty weak---for example three bedrooms share a main return in the hallway.  I'm concerned that a heat pump (lower air temp, etc) will exacerbate this flaw, should I be?

During the summer, 6 ton is probably serious overkill based on what I've been reading here.   Does that run a high risk of air quality issues, especially given the bad airflow design?

This is a great group, I've learned a bunch already, not the least of which that there are a bunch of nuances in geo that you ignore at your peril.  Thanks in advance...

The 3 ton with supplement and 6 ton standalone seems in line with your heat load. If electric heat is cheaper than propane, forget the propane for backup and go with a big heat strip and possibly a few electric space heaters.

Air flow is a concern, you would have to have a local HVAC guy tell you if what you have will work.

There is very little maintenance needed on a geo heat pump.

I would do a two stage 6ton with strip heat

If you have competent drillers, they should be able to handle any major surprises like hitting an artesian water, an underground gas pocket, an abandoned coal mine. There are numerous possibilities, most of which can be eliminated by consulting drilling logs of wells in your area.

If you go a two stage system, it will mitigate some of the summer problems you are worried about.

Good luck and keep us informed.

It is interesting to me that your installer offered nothing between the 3 and 6 ton. I also am unclear as to the capacity of the duct work. Ask for %of requirement provided with out supplemental heat.
Joe

Thanks for the quick reply.  PSNH is around $.15/kwh for electric.  Propane is $2.80-$3.00/gal.  Seems like heat strips (those are built into the heat pump air handler, yes?) are the right thing both from a operating cost and complexity standpoint.

I have a 5-year-old 50 gal propane water heater.  I'm reading that SDH is worth the trouble.  Can I just tie the GTHP into the existing water heater?  I assume that the SDH would feed into the existing heater, which would then feed the hot water lines in the house, yes?

Yes, after reading this forum last night I'm also curious about the limited number of choices offered.  I'm definitely going to get a 2nd opinion if not a 3rd.  The first guy seemed very competent, if a bit underleveraged on the nuances.  At the moment I'm doing the load estimates myself, for example.  But he allegedly does a bunch of geo up here, and the load estimates I worked out seem to align with his assessment of how much the house would need.

The duct work is something of an opaque issue to me, I need to get clarification (and 2nd opinion) on that.  He seemed to be saying that the original airflow capacity wasn't enough even for the original HVAC design of the house.  And from what I read hear on the forum, GHP tends to require higher capacities due to the lower air temps in the ducts during the heating season.  But he was also going to break the house into an upper-floor/lower-floor zone, so there would be a lot happening at once.

As far as your load, I'd lean towards a 4 ton. Like Joe says, it's kind of weird that the guy didn't offer anything in between the 3 and 6 ton units. 4 tons shouldn't overdo your cooling so much, but should meet most of your heating need.

Definitely get some more quotes/options, and keep us posted. Good luck.

Spoke with two other outfits on the phone this morning.  The first guy seemed very knowledgeable, had some good suggestions for the attic problem.  He also pointed out that infiltration is the best bang for the buck (going from my current .6 ACH to .3 reduces the heat loss from 56K to 46K!).  Based on the numbers I reported to him, he is thinking a 4-5 ton, dual-stage Water Furnace system.  But who knows, my numbers may not be completely accurate.

The 2nd outfit, based on the same numbers, is thinking 8 ton(!).  They admit that this is primarily driven from square footage, not the loading numbers I'm getting in HVAC calc.  Which doesn't make any sense to me.  I'm sending them PDF's of the HVAC Calc reports, as well as the rough builders blueprints and we'll see if that number changes at all.

Although I find it hard to believe I would need 8 ton, I wonder about whether I'm really off on my HVAC calc numbers.  The limitations I'm facing are as follows:

• I'm using interior dimensions on rooms.
• I'm not accounting for every single cubby in the house, or the staircases.
• To accommodate the above, I did round up on wall area dimension, which seems to be primary driver of the BTU numbers.

If you look only at outside dimension, you end up with around 3100 sq ft above grade, 500 below.   My HVAC Calc numbers (based on inside dimension, and I revised them upward after re-measuring and looking at the prints) show 2400 sq ft above, 500 below.  I'm unclear on how precise I have to get, especially when the wall/ceiling dimensions are probably about right.

So at any rate, the new, larger numbers show 27K gain/62K loss at .6 ACH, 25K gain/51K loss at .3 ACH.  So I'm still not seeing why it would be 8 ton.  They were also pretty insistent that it's better to overbuild, which runs counter to the other information I've seen.

The actual installers here would have a better answer, but my inclination is unless your house has some huge oddity, I wouldn't even bother further discussions with the 8 ton recommendations.

This is a huge red flag.  They just want your money,  not what is best for you.

You have a great resource on these forums that gives you an  advantage over most homeowners who only know what the installer tells them.

Don't be afraid to call them on it when the make outrageous or erroneous statements.

Oversizing HVAC systems is so wrong that bidder deserves no further consideration.

You seem to have the loading dialed in. Crucial to this will be the ductwork. Duct barely sufficient to AC a NH house in summer will likely fall far short of what is needed for geo heat through a New England winter. Each room / zone's load must be individually accounted for and sufficent duct in place. Placement and throw are important to comfort as well - wash cold walls and windows with warm air - attack the load.

Most two speed units low stage is 70 % of high - make sure any zoning system accounts for that.

I second (or fourth) the opinion that 8 tons merits no further discussion. Nor would I have a conversation with any one using square feet as a guide. We all get a rough idea based on SF but it's not a design calc. I would have guessed your house at 4-5 ton, and now that you have an actual heat load, the contractor should be able to put it into cost projection software and choose 4 or 5T based on which unit satisfies about 90% of your requirement unassissted. If the system is being zoned duct work is less likely to be undersized.
Find another contractor for a third opinion and ask for references.
Joe

I haven't heard back from my email to the 8-tonners, and I won't make a big effort to close the loop.

In the house, the returns are all near the center of the house, the vents along the shell.  The big problems I have are:

• Big difference in temperature between the two floors, and I've never been able to balance the venting to overcome the single-zone limitation such that the house is more even.
• The 2nd floor bedrooms skimped and all share a return in the hallway.  As the kids are getting older it's more practical to work around this by just leaving their doors cracked at night.
• The two upstairs rooms furthest away from the air handler do not get sufficient heat/cooling, and are noticeably too cold/hot.  I'm hoping that a ducting upgrade will cure that, although I'm sure that the shared return has something to do with it also.

Will definitely try to get into details with the candidates on their next site visit to see what I think of their analysis and proposed solutions.

On the comfort between levels, in the heating mode, a geothermal heat pump will increase the comfort anyway. Just because of its lower heating temp. and longer run times. You'll find that the air will mix more completely before it shuts off, and you won't have stratification happening. It will help alleviate the problems you're having with heating the upstairs. However, it won't completely take care of the problem. If the room can't get any air, it won't be able to mix/circulate as needed. It will still, though, be more comfortable than what you have now.

Ended up speaking with a local drilling outfit on Friday afternoon.  The guy I spoke with seemed very knowledgeable and was able to discuss the nuances of geo wells with ease.  Their rough rule of thumb is $2000-2200 per ton for the well, assuming 40' of casing and up to a 50' run between the house and the well. 

His suggestion was to do a standing column if they hit enough water, which he figured at 2gpm for a 4-6 ton system.  The argument was that the a standing column is more efficient than a closed loop, which makes sense.  If they don't get enough water flow, or can't get the water column tall enough, then he said they could fall back to using a closed loop.

The story held together pretty well for me.  That sound about right?

FWIW, they also have worked closely with the first guy I've been dealing with, and gave a glowing recommendation.  They have only done limited work with the second guy.  He agreed that the 8-ton estimate was way out there, but hadn't dealt with the outfit who recommended that.

A heat strip is an electric resistant heater that's installed between the Air handler fan and the duct work.

For my 3,500 sq ft house I'm running a 4 tons Geo downstairs and a 3 ton ASHP upstairs. I'm suprised that a 3,100 sq ft house can be heated with only 4 tons. How many floors does your house have?

It really depends( on a thousand things ) .  I have a 3400 sqft house with a 4.5 ton heat pump.  I probably would be OK with a 4 or maybe even 3.5 ton.

Keep in mind that square footage plays a small part in the final heat load of a structure.

Two floors, 40x30 main footprint with a single-story 14x24 pitched ceiling bonus room on the end.

I've gone over the HVAC Calc inputs several times, trying to round up on wall/ceiling area and rounding down on R-factor to get worst cases.  With the current leaky .6 ACH I still get 62K heat loss, and if I fix the leaks and increase the attic R-factor than it drops down to around 50K. 

Based on that it seems like 5 ton would do it, 6 if I thought that I was absolutely missing something big in the HVAC Calc inputs.

I just loaded a 4000 sf house today that only needs a 3 ton. It has way more to do with insulation, windows, and infiltration than square footage.

tuffluck......can you expand?....How was that house built? R-value....construction? Brick....ICF....SIPS.......etc.....??.....Location?.....