New Construction HVAC decisions. Geothermal vs. alternatives with upgraded envelope.

[MGH PA]

I posted this over on the GBA forum as well, but I've posted here quite a bit regarding my build plans. I will attach a copy of my floor plans as well for reference.

I know these questions are hard to answer online, but I will do my best. Most of the information I receive locally is from HVAC suppliers pushing a particular system.

So, a little information that will help.

We are building (in June) in Northcentral PA, in zone 5, on 25 acres. We're at ~1000ft of elevation with a mixture of shale/loam soils. We have no access to NG. It's Propane, oil, or electric. Current rate is around $.11/kWh. We have ~6300 HDDs.

We arebuilding a single story with a fully exposed walkout basement. 2986 sq.ft on the first floor as well as the basement. Basement will be ICF with R10 subslab insulation. I'm planning on putting Creatherm panels and running per for a future hydronic system. On the main floor, we are using traditional 2x6 with NuWool, and R49 spray in ceilings. We're using Low E Paradigm windows, and have ~708 sq.ft of glass.

We were quoted by two different contractors for a Water Furnace 5 series, 4ton system, single zone with electric backup at ~28,000 before tax credits. That was for vertical well systems. Only one contractor was willing to do a horizontal loop, and that came in at $24,000. Adding a desuperheater, and extra zones would drive the cost well north into the mid to upper 30,000 range before tax credits.

Right now, we're considering adding foam sheathing to the outside of the building envelope to help eliminate thermal bridging and increase our R value above code (waiting on the quote from the contractor as he originally quoted me for R5, but I need a minimum of R7.5 with a 2x6 wall). I think in doing that, along with the insulated slab/hyrdonic heat, that we might end up better in the long run with a higher efficiency ASHP + the hydronic and possible wood stove for rare sub zero nights/days.

Granted, I'm not a pro, so I may be overlooking some obvious things, or maybe I need better estimates.

I would love to hear everyone's thoughts on this.

 

[RNeumann]

PM if you want to chat. It’s pages of info. Some stuff you are on the right track but most things need a tweak.

Check out buildingscience.com but don’t go overboard!

 

[EddieWalker]

With all building methods, you start with the basics and then try to improve from there. For heating and cooling, the two basic rules are that heat goes up and that wind goes sideways. Insulating the walls for heat is a distraction once you go beyond the basics. Wind is what is most important in the walls. If you can keep the wind out of the wall cavity, R13 is fine and R19 is pretty well maxed out. House wrap has helped a lot with this, but some of the new technology has a lot of promise. I personally believe Zip System is worth the extra cost over house wrap. An inch or two of closed cell foam on interior wall cavity is the ultimate wind stopper, but it's a lot of money and the return is sometimes never achieved. Windows have to be tape sealed and the space around them filled with open cell foam. Same with doors and every other penetration of the wall cavity. Attic space is simple. Max out your R value with insulation. R60 is becoming the norm. Foam is the best, but for attic space, blown in will give you the same R value for a lot less money. I personally go for 2 feet of Attic Cat blown in insulation.

For your HVAC system, SEER rating is what you are paying for. I think 14 is kind of the standard for most systems, and then the bigger the number, the more you will pay to buy it, but the less it will cost you to run it. I have an 19 SEER unit in my house. I was tempted to go higher, but the jump in cost was just too much. One thing to remember with HVAC systems is that just like cars, the most energy is used when it starts up. Ideally you want a system that runs longer then one that is always starting up for short periods of time.

Something else that is important to me is where its mounted. Seems like most new construction likes to put it in the attic. I've run into a lot of homes where the attic wasn't framed to do this. Either they put it on top of 2x6 rafters, that only allows you to insulate 5.5 inches for R 19 attic insulation under it, or they block off that cavity completey and there is zero insulation under the unit. In some homes, the build up a platform to mount the unit and it can be insulated under it. This needs to be done in the framing stage before the HVAC guys get there. You also need a way to get to the unit that does not destroy the insulation along that path. Your unit should have the filters changed every month, and bleach poured down the condensation drain at the same time. I get a lot of work every year from water damage to the ceiling of a house caused by the pan over flowing because the primary drain is plugged from sludge that built up because nobody put bleach in there, and the secondary drain is plugged up from insulation, debris or sludge. Sometimes it's not even sloped away properly and the pan overflows before water can get to the secondary drain.

In my house, and the house that I built for my parents, I made it a point to install the HVAC units in an area where you can get to them easily, and NOT in the attic. What I found surprising is that of all the HVAC companies that I called to bid on the job, only one agreed to put it where I wanted it. All the others said that they would only install it in the attic.

When dealing with contractors, especially when its something that you are not familiar with, be sure to talk to at least five. More is better. Just make it a point to not hire, or commit to anything until you have spoken to at least five. Some are very good salesmen, very personable and believable. Some are horrible in person. You don't know which one is honest until you do your research. Will they show up at midnight on Saturday night when you have a problem? Will they have a van full of parts to fix your problem? Anybody can sell a system and make a profit off of the commission, but the company that is there when you need them is a lot more important then the one that is a couple hundred bucks cheaper then the other guys.

 

[jk96]

Make sure your HVAC guys all do a load analysis with your quotes and compare. We have geothermal and love it but our guy missed the mark by a bunch. We have way more tonnage than required and it took some work on my part getting the most efficiency out of our system. We have multiple zones and all were short cycling leading to a not very efficient setup. Zone bleeds, some programming of the zones to trick the system into always running in the lowest stage one regardless of how many zones are calling and a couple of other tweaks and I now have a very efficient setup.

Just to give you an idea of how far off he was we have two 4 ton units each controlling half of the house plus backup heat strips for the coldest temps. Units are 2 stage compressors and I have the zoning tricked into never leaving the lowest stage one (about 60% of unit capacity). Breakers for heat strips have never been turned on. Last week we had near record breaking temps at -12 overnight. My units still cycled on and off a couple of times overnight and had no problems keeping the set temp of 73 in our home in stage 1. This tells me we could have probably got by with only 4-5 tons. Depending on which waterfurnace unit you are getting I think they have scroll compressors that make the load calcs a lot more forgiving though, at least if you end up oversized.

Finally make sure you do a blower door test prior to sheetrock. Super easy way to find air leaks. If you want to make it interesting use a theatrical fogger inside the home on a day with no wind and reverse the blower door. You can walk around your house and see every area that is leaking. Also make sure your quotes include an HRV or ERV for fresh air exchange on a tight home. Another mistake by our HVAC guy for not including it. He told us do to the size of the home we would not need one. I think he underestimated how tight I was able to seal up our house. We had to add one after the fact once I started monitoring our co2 levels.

 

[MGH PA]

With all building methods, you start with the basics and then try to improve from there. For heating and cooling, the two basic rules are that heat goes up and that wind goes sideways. Insulating the walls for heat is a distraction once you go beyond the basics. Wind is what is most important in the walls. If you can keep the wind out of the wall cavity, R13 is fine and R19 is pretty well maxed out. House wrap has helped a lot with this, but some of the new technology has a lot of promise. I personally believe Zip System is worth the extra cost over house wrap. An inch or two of closed cell foam on interior wall cavity is the ultimate wind stopper, but it's a lot of money and the return is sometimes never achieved. Windows have to be tape sealed and the space around them filled with open cell foam. Same with doors and every other penetration of the wall cavity. Attic space is simple. Max out your R value with insulation. R60 is becoming the norm. Foam is the best, but for attic space, blown in will give you the same R value for a lot less money. I personally go for 2 feet of Attic Cat blown in insulation.

For your HVAC system, SEER rating is what you are paying for. I think 14 is kind of the standard for most systems, and then the bigger the number, the more you will pay to buy it, but the less it will cost you to run it. I have an 19 SEER unit in my house. I was tempted to go higher, but the jump in cost was just too much. One thing to remember with HVAC systems is that just like cars, the most energy is used when it starts up. Ideally you want a system that runs longer then one that is always starting up for short periods of time.

Something else that is important to me is where its mounted. Seems like most new construction likes to put it in the attic. I've run into a lot of homes where the attic wasn't framed to do this. Either they put it on top of 2x6 rafters, that only allows you to insulate 5.5 inches for R 19 attic insulation under it, or they block off that cavity completey and there is zero insulation under the unit. In some homes, the build up a platform to mount the unit and it can be insulated under it. This needs to be done in the framing stage before the HVAC guys get there. You also need a way to get to the unit that does not destroy the insulation along that path. Your unit should have the filters changed every month, and bleach poured down the condensation drain at the same time. I get a lot of work every year from water damage to the ceiling of a house caused by the pan over flowing because the primary drain is plugged from sludge that built up because nobody put bleach in there, and the secondary drain is plugged up from insulation, debris or sludge. Sometimes it's not even sloped away properly and the pan overflows before water can get to the secondary drain.

In my house, and the house that I built for my parents, I made it a point to install the HVAC units in an area where you can get to them easily, and NOT in the attic. What I found surprising is that of all the HVAC companies that I called to bid on the job, only one agreed to put it where I wanted it. All the others said that they would only install it in the attic.

When dealing with contractors, especially when its something that you are not familiar with, be sure to talk to at least five. More is better. Just make it a point to not hire, or commit to anything until you have spoken to at least five. Some are very good salesmen, very personable and believable. Some are horrible in person. You don't know which one is honest until you do your research. Will they show up at midnight on Saturday night when you have a problem? Will they have a van full of parts to fix your problem? Anybody can sell a system and make a profit off of the commission, but the company that is there when you need them is a lot more important then the one that is a couple hundred bucks cheaper then the other guys.

Thanks. Very help as usual. I’m making it a point to have great air sealing to help cut back on infiltration. We are using ZIP, and the NuWool is a damp spray that gets put in AFTER all seams and penetrations have been sealed. Part of me feels this should be more than sufficient, but I also worry about thermal bridging.

I’m going to have all utilities placed in the basement central located for what it’s worth.

I just get frustrated because we live in a “low tech” area where I feel like most of the subs are used to building what they’re used to and scoff at the newer ideas (like the use of Manual J’s to properly size an HVAC system).

My GC is great about staying up to date with current building methods, but in the areas he subs out, I’m finding even his good subs don’t know all I want them to know to complete some aspects of the project.

When I’m paying the bills, and I want my house to perform a certain way, I’m going to be extremely disappointed if it doesn’t because some sub didn’t or couldn’t bother to stay up to date on proper building science.

 

[MGH PA]

Make sure your HVAC guys all do a load analysis with your quotes and compare. We have geothermal and love it but our guy missed the mark by a bunch. We have way more tonnage than required and it took some work on my part getting the most efficiency out of our system. We have multiple zones and all were short cycling leading to a not very efficient setup. Zone bleeds, some programming of the zones to trick the system into always running in the lowest stage one regardless of how many zones are calling and a couple of other tweaks and I now have a very efficient setup.

Just to give you an idea of how far off he was we have two 4 ton units each controlling half of the house plus backup heat strips for the coldest temps. Units are 2 stage compressors and I have the zoning tricked into never leaving the lowest stage one (about 60% of unit capacity). Breakers for heat strips have never been turned on. Last week we had near record breaking temps at -12 overnight. My units still cycled on and off a couple of times overnight and had no problems keeping the set temp of 73 in our home in stage 1. This tells me we could have probably got by with only 4-5 tons. Depending on which waterfurnace unit you are getting I think they have scroll compressors that make the load calcs a lot more forgiving though, at least if you end up oversized.

Finally make sure you do a blower door test prior to sheetrock. Super easy way to find air leaks. If you want to make it interesting use a theatrical fogger inside the home on a day with no wind and reverse the blower door. You can walk around your house and see every area that is leaking. Also make sure your quotes include an HRV or ERV for fresh air exchange on a tight home. Another mistake by our HVAC guy for not including it. He told us do to the size of the home we would not need one. I think he underestimated how tight I was able to seal up our house. We had to add one after the fact once I started monitoring our co2 levels.

That sounds like a ton of tweaking you had to do. I feel like the tonnage calcs that most of the subs are using is just based on square footage and basic layout. Most didn’t ask about U factor of the windows, glazing square footage, subslab insulation, wall construction, etc. They’re essentially “ballparking.”

 

[Raspy]

MGH,

I'm wondering how much sun you get in the winter and if thermal solar might work for you. It will never do 100% in any case, in the winter. But what it does give and the simplicity of it, make it very appealing. Plus, Spring through Fall it can offer 100% of your heat and hot water needs when delivered through an in-slab radiant system. Again, with a very simple and reliable setup that requires no well and no heat pump.

You mentioned running PEX for a future hydronic system, but I'm wondering why you don't use the radiant as your primary delivery system? Radiant floors can use the lowest delivery temperature and offer the greatest comfort while operating silently. And that system is pretty much required for good solar efficiency.

Your environment may be way different than mine, but in my case, I have about 1,800 sq ft of living and 1,000 sq ft of attached garage that is also heated. Both are an 8" thick radiant slab. Total 4 zones, but mostly operated as two. We live at 4,900 ft and get good sun, with a some days of overcast and snow. Lows are usually high teens. It's a single story, steel framed house, on a slab, with an attic. R-38 in most of the ceiling and 22" of blown in over the living room. R-19 or better in the walls. From mid March through November my water heater stays turned off and our heating needs are handled by the solar with no backup. November through mid march is the season we use some backup and have an electric water heater to top off the pre-heated solar water. My backup energy source is diesel fuel in a conventional boiler rated at 85%. I sacrificed some efficiency for absolute reliability and I've done some simple modifications to make it even better. Last year I used 38 gallons of backup fuel for the entire heating season., but I'm expecting about twice that this year. Our electric bill, including the mother-in-law unit and keeping the pump house warm, gets up to about $140 to $160 in the winter and down to $40 in the summer. We also have a wood stove. I like wood heat and it makes a good backup during any power failures or extended bad weather. During extended periods of overcast, it's so easy to get immediate heat by lighting a fire in the morning. We use less than a cord per year overall and prefer the solar radiant as much as possible.

Managing the system really helps it produce more. With an 8" slab, I can dump solar into the floor for hours on marginal days to keep the panels as cool as possible. This raises their efficiency and reduces heat loss to the environment from them. Or, at the end of a day of collecting, we can heat for hours from the storage. The floor becomes part of the storage and is maintained at a comfortable temperature most of the time. All of this "management" is fun, but not needed as I can simply set the thermostat and let the system work.

I installed (6) 4'X10' collectors ina drain back system that uses fresh water for storage and transfer from the collectors. It cannot freeze because the panels drain by gravity unless they are collecting. This means absolute freeze protection, no glycol and a very simple heat exchange system. Storage is (5) 120 gallon solar storage tanks.
So, we have the drinking water, that is also the storage water, the collection loop and the radiant floor water loop. The system automatically switches from solar to backup, if given permission to do so at the thermostats. In the Spring through Fall we have 650 gallons of hot water on tap and cannot run out.

The beauty of the system, besides it's efficiency, is is ridiculous simplicity. Everything can be reached for service if needed, pumps are off the shelf, controls are mostly wall thermostats with a differential solar controller and a setpoint controller. The boiler is old school with proven reliability and parts are easy to get if needed. The heat involves no blowing air, no ductwork, no geo horizontal array or well and the tile floors are warm. I have enough backup diesel stored for at least 12 years of use and will not have to buy any more for that period, so price fluctuations are not a problem. I just bought 200 gallons to make up for the last four years or so, because there was price dip, but it wasn't necessary. I don't like propane for heating, but did install it for the kitchen stove.

 

[jk96]

That sounds like a ton of tweaking you had to do. I feel like the tonnage calcs that most of the subs are using is just based on square footage and basic layout. Most didn’t ask about U factor of the windows, glazing square footage, subslab insulation, wall construction, etc. They’re essentially “ballparking.”

It was and was very frustrating for a bit as the HVAC contractor was not offering much help. I think he was worried I was going to press for new units. The short cycling was leading to humidity issues in the summer as well. In the end through a lot of head scratching I ended up doing the following.
1. Slight zone bleeds so when one zone calls we are heating or cooling other zones as well. Not enough to overheat or cool them but essentially maintaining longer before they call for hvac.
2. Added a zone to each unit that does not exist. My units require each zone to be given a % of total. When greater than 67% of the zones call for heat or cooling they go into stage 2. By adding an additional zone I was able to make sure that even when all zones called at once the total did not exceed 67%, thereby always keeping them in stage 1.
3. By keeping units in stage 1 I was able to eliminate 1 of 2 pumps for each unit. I'm now running 2 pumps instead of 4.
4. New thermostats that allowed me to increase the temp swing differential between calls.

By doing all of the above I was able to go from non-stop 5-6 minute calls from multiple zones to less frequent 12-15 minute calls. My efficiency increased dramatically. On a bonus side my loop temps even toward the end of winter or summer are really good since my loops are oversized for the units in stage 1 operation.

Anyway. Apologies to the op for the hijack. Just learn from my mistake in sizing. The system installed and the ductwork done were fantastic. Better than a lot of commercial work however it was grossly oversized.

 

[dodge man]

We had geo put in about 4 years ago. We had the horizontal loops put in using directional boring. Going by memory here but it cost 20k and after the tax breaks cost 13k. We also pay a few pennies less for KWH on the geo. We already had ducting in place. I think ours is a 4 ton 2000 sq ft house with full basement single zone. Works good.

The tax breaks is what steered us into geo. We used propane before.

 

[PEJ5]

Insulation is a one time cost and so inexpensive compared to years of energy consumption. I know I am in a different zone but look at Canadian insulation methods. R22/24 in walls plus R10 outside under siding for R32+. R60 in the attic. Methodologies vary for basements, especially those with walkout fronts, but insulate well outside and under the slab to start with and add inside based on outside.

Another option is to rearch passive solar construction. Methods can be adopted for most house designs.There is a contractor around building homes that use a 2000 watt heater, yes, in Canadian winters.