There are several obvious questions.

What size is existing furnace and AC?

What size is your home?

What size is each zone?

Why an 80% eff furnace?

Why not a two stage AC condenser?

Post back.

IMO

• The existing furnace came with the house and is a way oversized beast: Lennox 150K BTU; that being said, before we replaced them, there was a lot of square footage of single pane aluminum framed windows (its making me cold just thinking about them). We have no current air conditioning.

• The house is a 1960s raised ranch with ~1800sf on the main level and with ~1200sf on the lower level. There is R20 in the attic, new glazed triple pane windows, three foot soffits east and west, and good high canopy tree cover.

• The zones are ~900sf main level bedrooms, ~900sf main level living, ~1200sf lower level.

• We have an internal / front-center of the house chimney which coupled with the front door and windows makes the placement of an intake and exhaust for a gas high efficiency furnace and exhaust for a gas high efficiency water heater problematic from a code standpoint and undesirable from an aesthetic standpoint (pipes next to front door, if possible at all).

• I was considering the same and even a dual fuel system, if you want to hear those thoughts as well. What are your thoughts?

The zoning for the house already exists and works with the current single stage, single speed, oversized, 150K BTU Lennox beast. We get warm and fast, but I'm unsure whether it trips off or is shut down by the existing thermostats and zoning control board.

The Manual J apparently yielded a somewhat higher than 60K BTU heating load and a somewhat less 2.5 ton cooling load.

The 80K BTU & 80 AFUE furnace produces 41.6K / 64.0K at the two stages.

We are looking for dehumidification as one of the primary drivers for the air conditioning unit.

Several more questions please.

How would you describe the insulation qualities of your home?

Is the lower level at or even partially below grade?

What is electric rate? This might determine whether a HP condenser would be worthy of consideration. I also might consider a two stage condenser whether AC or HP.

Where will furnace be located?

And the primary reason for the 80% two stage furnace is the venting of a high eff condensing model would be problematic or more due to the aesthetics and visual of the possible location of waste pipes?

It would seem that even an 80% eff furnace properly sized will save you substantial money over the obvious current oversized model.any short cycling with existing furnace?

If you have the load calc for both heating and cooling broken out for each zone, I would like to see them.

Ductwork has been surveyed by dealer? You have adequate return for each zone? Any modifications to be performed?

R20 in attic? That doesn't sound correct for Northeast. Please recheck.

You mentioned you would be furnishing three new thermostats?...I assume these are really just on/off thermostats as the zoning board will actually control the HVAC.

Your quoting dealer is experienced with zoning and has good demonstrated knowledge of your existing zoning board?

I realize you are in a large metropolitan area in expensive Northeast but pricing does seem high. Of course I can't see the job from here nor do I have full understanding of scope of work. However, from what you have described, I have not heard anything of a special or extraordinary situation.

Post back.

IMO

Thanks for the replies tigerdunes.

• The insulation is average to good. There is about seven inches of fiberglass batt in the attic and all obvious thermal chimneys have been insulated (i.e.insulation over lighting cans, etc). We have insulation in the walls, but it would be that typical to 1960s and fair at best. We are considering adding another twelve inches of fiberglass batt to the attic but must address certain existing storage complexities.

• Of the finished basement, 800sf is below grade and 400sf is at grade (400sf dedicated to a lower level garage is at grade but not included in the figures).

• Electric (NStar) is $0.162/KWh unit cost (delivery and generation costs; fixed costs not included). Gas (National Grid) is $1.3463/Therm unit cost (transmission, distribution and supply costs; fixed costs not included).

• The current furnace is and new furnace will be located next to the internal chimney in the front-center of the house, primarily because of front-center existing duct work but also for space considerations.

• The venting of a high efficiency condensing unit would be somewhat problematic and aesthetically unappealing. If we went with a high efficiency furnace, then we would also like to install a high efficiency gas hot water heater, because it seems counterproductive to install a smaller flue liner for the existing gas fired hot water heater. Due to setback requirements and snow requirements, there may be a very tight area in proximity to the furnace where two exhausts and one intake could be installed; that area is close to the front door and would be unappealing to my wife and would require some additional carpentry work. I don't believe we have a straight shot up the existing flue because of the main floor fireplace, but I have yet to check.

• We are unsure whether or not the existing furnace is short-cycling (i.e. shutting itself down for protection reasons). The cycles are certainly short, but I would guess not, only because we do reach thermostat set temperatures, although it wouldn't be a big surprise.

• We have not received the Manual J; we have only been told the results from a whole house standpoint. We are requiring the receipt of the load calculations prior to installation but after a vendor has been picked.

• The ductwork has been examined by the dealers. We have one large single return for the main level living zone, one large single return for the lower level zone, and a small return in each bedroom in the main level bedrooms zone; the returns are coupled as a common return prior to the furnace. The zoning, ductwork and returns are very good for the 1960s, but uninsulated and based on five inch supplies; so, the system would be undersized for today, I believe. All ducts are internal to the house, although some run through the garage; all ducts are enclosed and finished, other than those in proximity to the furnace. No modifications will be performed to the ductwork, other than any transition needed to the new furnace.

• There is seven inches of fiberglass batt between the eight inch ceiling joists (R20).

• The zoning control board will control the HVAC system. The new thermostats are dumb, although nicely programable and aesthetic (Aube/Honeywell TH141). In addition to a common (C), the thermostats accept 24V (Rh), heating (W), 24V (Rc), cooling (Y), and fan (G). The new thermostats do not have any second stage inputs or reversing valve input; we have five wires at our existing thermostats; the new thermostats can be battery powered.

• The dealers are familiar with zoning, and with either a dumb-simple zoning control board for heating and air conditioning or a smart acculink system; they are less familiar with the combination of smart zoning control board and dumb thermostats or a dumb-sophisticated zoning control board and dumb thermostats. I am personally unimpressed with the smart thermostat systems; to much unnecessary/unused information; to expensive; to large and prominent. What are your thoughts?

• The job is simple, although the air conditioning installation would be new but typical.

It seems that I should have about $2500-$3000 in air condition installation cost and about $2500 in furnace installation cost and about $1000 in miscellaneous cost (including the $150 zone control board and the media filter), for $1600 in air conditioning equipment cost (2.5 Ton, 15 SEER) and $1800 in furnace cost (80K Btu, 80 AFUE). That would be $6000 to $6500 total cost.

What is your experience for pricing of such a system?

The furnace and hot water heater flue is not a straight shot, although it appears to be a smooth gradual transition, and is an eight inch by twelve inch flue. Is there any reasonable way to run the pipes for the exhaust and intake of a condensing furnace up a non-straight flue?

The primary driver for the HVAC system replacement is the installation of the air conditioning, although the furnace is certainly due for a change. A primary consideration for the air conditioning is humidity control.

Your electric rates seem a bit high for duel fuel, but there are on line calculators for that.

FYI..I paid around $7500 for a Trane HP 2.5 15 SEER unit a few years ago, mid Atlantic. Your price doesn't seem out of line for me for the Boston area.

Thanks for the reply weedmeister.

Is this calculation/formula correct for determining the unit cost point of an air source heat pump vs a gas furnace for my particular situation (electricity unit cost of $0.162 / KWh and gas unit cost of $1.3463 / Therm and an 80 AFUE furnace efficiency)?

KWh / $0.162 x COP[unit cost point] x Therm / 29.3 KWh = Therm / $1.3463 x 0.80
COP[unit cost point] = 0.162 / 1.3463 x 29.3 x 0.80 = 2.82

Therefore, is an air source heat pump more economical on a unit cost basis, if it can deliver greater than 2.82 COP at a given temperature?

This post was edited by liameknuj on Mon, Apr 22, 13 at 6:21