Wednesday, February 13, 2013

HVAC and Plumbing started

Now that the roof is on, windows and doors in, I called in the subs to start their work.  While the hvac design was a massive indecisive headache for me, I landed on going with the tried and true system that will work.  Having gone down the road of geothermal, heat pumps (both ducted and mini split units) and traditional gas furnace/ac unit...I ended up selecting the traditional gas furnace.  Several reasons backed this decision.

First off, gas rates in our area are very low.  To make it more appealing, the gas company (Black Hills Energy) has some very attractive incentives for energy efficient design.  In fact, they are the best out of Alliant and MidAmerican Energy.  Their new home construction Energy Star 3.0 package gives a $5000 rebate if gas is used for the furnace and the water heater.  Obviously the home design exceeds ES3.0 guidelines, so now we just have to make sure the HVAC meets the requirements. 

Since the gas rates are low, it makes even a furnace running at 95% efficient on par with heating costs with an air to air heat pump.  Obviously the efficiency of the ASHP (air source heat pump) drops as the exterior temps drop, with a shut off around 15 degrees.  I needed a backup heat source anyway, with the choices being a gas furnace or an electric coil in the blower.  Electric heat, while a 1:1 efficiency, is an expensive way to heat.  Electric rates are so so, so the all gas furnace made more sense in this case.  Cooling costs using the ASHP were lower than the AC unit, however not that much.  With the ASHP, that would be classified as the main heating source, thus I would not get the $5000 rebate.  There are rebates to be had from Alliant Energy (power supplier) but they are not nearly as high.  Mix the lower rebates with a higher cost of equipment (ASHP being higher than a furnace/AC) it just did not make any sense.  The pay off was negative years in this case.

So we move on to geothermal heating and cooling, or ground source heat pump (GSHP).  Many people think this is the thing to be had, and it is certainly is expensive.  But when you start to dig into the technicalities of it, it did not make sense for our specific project. 

First off, it is an expensive system to install.  Being on a lot, we would need to go vertical wells as opposed to the more cost effective horizontal wells.  These cost around $2500 per ton of heating, and the heat load would require 3 tons.  Technically a 2 ton system would handle it, but a 3rd well would be put in to account for ground temp drops in the coldest of winter when the delta is the highest for heat loads.  This is $7500 right there.  The actual air handler and pump (that pushes the water/glycol mix through the buried piping) equipment is not that much more than a typical furnace system.  However include a filter and HRV along with all of the ductwork installation, that part is around $15,000.  Add the cost of the wells and the total installed system is around $23,000.  While are area geothermal installs is pretty cost effective compared to other parts of the country, lots of math still needed to be done to see if that high upfront tag worked itself out.

Geo is efficient.  I was looking at the Waterfurnance Synergy system.  It was pushing a 5.0 COP, which is extremely good, possibly the highest on the market.  However what that number fails to take into account is the other power requirements geo has, such as the pump running as well as the fans and blower.  This drops the overall efficiency, and the real world COP is closer to 3.0.  Still very good.  Still 3x more efficient than electric heat.  Using the electric rates this gives a cost of roughly $30/month per year.  Factor in the 30% federal tax rebate and rebates from the power company, this puts geo approximately the same price as the bids for a high efficient gas furnace and AC but being a 300-500% efficient system.  Seems like a no brainer. 

Getting back to the furnace, the unit I am using is the Lennox SLP98V.  It is a variable capacity 98% efficient gas furnace.  This differs from a dual stage furnace by allowing it to run anywhere from 35%-100% capacity.  With the low heat loads of the house, this allows the furnace to run at low speed and only ramp up to higher speed if needed to handle the load on the coldest nights.  With the heat loss of the home will be very slow, the furnace will rarely run at high capacity. Obviously this furnace is a very efficient gas furnace backed by a very good brand.  With it being a gas system, this qualifies it for the $5000 rebate from Black Hills Energy since it is about 96% efficient to satisfy the requirement.  With the low gas prices and high efficient furnace, the cost averages to around $40/month for this route...only $10 more dollars, or $112 dollars more a year than geothermal.  With the NET upfront cost of it being $6000 installed less than geo, this put geo  at over a 50 year payback, excluding energy rate changes obviously.  Another down side with the geo rebates is the federal tax rebate.  The equipment still needs to be paid for upfront and then wait for the tax rebate.

Here is a link to the Lennox furnace.

With all of that being said, here are some progress pics (very few currently, more to follow later) of the system getting installed.  In order to meet Energy Star 3.0 requirements, the ductwork needs to be sealed to prevent air leaks and to provide the require CFM of air to each space.  The ducts get tested with a duct blaster, which basically blows air into the ductwork and they test how much air leaks out before it gets to the space it is supposed to be feeding.  All joints in all pieces of ductwork gets sealed with mastic paste.  The return ductwork (seen below) is thermal pan (cardboard covered in foil basically) and gets sealed too. 

In order for the thermal pan to be sealed, I had them install blocking above the ducting.  Typical thermal pan install would just have a piece stapled across the stud bay.  Obviously this would allow a lot of air leak into the stud bay.  Once the drywall is on it could also bunch it up.  By installing the blocking and a metal flange, this allowed them to caulk the thermal pan to the block and stud (as you can see) and provide a strong backing for the seal to be made to the drywall. 

Plumbing has also started. Not as much to report here, its typical pex and pvc piping.  We went with a full fiberglass tube/shower unit in the main bath to allow good cleaning without caulk joints or grout lines.  I will tile above it to add some interest to it. 

laundry room rough in.

The EPS foam gets cared out and the pipes recessed into the foam. The plumbers are doing a great job with cutting the foam. 

Jacuzzi tub installed in our bathroom.  One of the few slurges in the home. 


  1. Good article, how long did it take you to install the jacuzzi tub?

  2. do not know...the plumbers installed the tub. I am guessing it did not take too long. It is set in mortar as well.

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  4. Thanks for this post. Its so great to find valuable information about the hvac services here in Omaha NE. Thanks again.

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