well, they cannot cut out for the registers until the drywall is in. but then again, it sure is easier to run ducts/wiring/other things and get large equipment in the attic when the drywall is not in the way.

since you are going spray foam, those folks need to KNOW where any ducting will be on any insulated walls before they spray. it is a PITA to have to pull the foam and the rock(if the sheetrock is done first) out to run the returns.

in my area teh HVAC guys usually come in and run their vertical ducts and termostat wires before the rock goes up. some will go ahead and mount the air handler inthe attic while the joists are open. then they come back and do final conenctions after the sheetrock is done.

i would ask my HVAC guy to do anything he can before the insulation and sheetrock is installed, then come back for final install afterwards.

Thanks davidandkasie. I think my HVAC guy's argument is that the ducts will get lots of "junk" in them if put in before the drywall.

The HVAC guy has already been here and marked and cut for returns and chases. I'll check about running the verticle ducts and wires adn the air handler. Thanks so much!

I had a geothermal system installed on my new home that we just moved into and the duct work (rough in) was done prior to drywall going in. If you are concerned about dust getting into the vents - then cover them up.

I can understand that the small registers in the floor could be done after drywall - but the return air ducts are usually higher up and in the walls - at least ours are that way. Maybe your house design would allow the return ducts to be done later - but it seems out of order to me.

I would also be worried about the plumbers and electricians putting their stuff in and then having to move it to make room for ducts. In my house - HVAC ducts went in first - then plumber- then electrician. I asked about this sequence and the builder told me that it is much easier to route plumbing and wire around ducts then the other way around. Seems to make sense.

The GT heat pumps did not get connected and turned on until after the drywall was finished. We were at that point mid summer and provided AC to make working inside more pleasant - but even that is not necessary. But you must have the HVAC system running before the hardwood flooring goes in. If you don't, you might have warping issues.

In my other house, they drywalled in the winter and used propane heaters to keep the place warm. If you have foam insulation, they can make the place nice and toasty. I think these heaters are safe - they are routinely used for your conditions. Otherwise - the construction industry would would just stop in the winter where it is too cold.

Here are some other tid bits I learned about my GT system. Maybe these might help you out.

One thing you should watch out for with the geothermal system is something I learned the hard way. Every sub in there - once the heat got turned on - thought they should turn up the heat to 78 so they could run around in T shirts. I routinely had to cut the heat back to 68 degrees - which is even too warm for me - but the max I wanted them to run it at. I recommend putting the thermostats inside lock boxes so that only you and the building supervisor can control the heat. There are times when more heat is needed (like when the hardwood is stained and finished) but all other times nobody should mess with the stinkin T stats.

One of the other issues we had was subs who kept leaving doors and windows open. GT heat systems are great - but they do not work well with a wide open door and freezing air coming in all night. Svereal times I showed up to the house in the morning and found this and the auxiliary heat on which is essentially a giant toatser and money pouring down the drain. So visit the site often and make sure that things are buttoned up each night.

Another thing we just discovered. With these recent extreme cold conditions (we live in the Blue Ridge Mtns in VA) where outside night temps were at or below zero, we found that one of the 3 heat pumps kept kicking on the auxilary heat. Turned out that the guys who installed the system (during the summer) forgot to add enough antifreeze to the mixture running in the loop field pipes. So the water mixture was turning to slush and not geeting a good heat exchange. After adding about 30 more gallons of glycol to the mixture - system is operating great.

My system has 2 pumps to push the water through the loop field. When the system was first installed, the electrician wired it up so that both pumps were running continuously. So I thought both pumps had to be on. Then we founnd out - after 3 months - that one of the pumps is a backup and we need only one pump running. This cut the electric draw for the GT pump system in half - and that means lower bills.

I also learned that with GT systems, it is best to keep the thermostats on a constant temp. They are not efficient when you crank up or down the heat/cooling by more than 2 or 3 degrees. Tstat timers - which we used on our other home with natural gas heat - are not a good idea with GT systems. If you try to drive a GT system to crank up the temp too much - the AUX heat will come on - and you don't want that to happen.

Finally - I installed humidifiers on 2 of the 3 heat pump units. My HVAC contractor told me that it is best to use warm water for the humidifier supply with a multi-stage GT heat pumps. After installing the units I can see why. You must hook up the humidifier air intake to the return air side of the heat pump - just after the emergency heat packs. This return air supply is sucked into the humidifier unit, passes through the filter, and then on into the supply side. If you run cold water through the humidifier filter - then you are taking hot air and cooling it down - so th eprocess is not as efficient as it could be with warm/hot water. If you are planning to install humidifiers - I recommend having the plumbers put in hot water supplies near the HVAC heat pumps sp that you you can feed the humidifiers warm/hot water.

Best of luck.

I can't see any sense in not roughing in the ducts before the drywall. Our builder just put scraps of metal over the outlets to protect from crud falling in. That said, the heat itself will not be running until well after the rough.

To Sniffdog:

We are looking at geothermal on our build in 2009. Where did you learn all your information on GT? What systems are good/bad, etc. Cost versus Electric heat for install, etc. Any good websites? Thanks

ChemE

Thank you for the responses. I'm off to talk to Mr. HVAC man.

our "guy" told us that he recommends waiting until the drywall is up and primed before they run the duct work.

I've been building for 20 years and I haven't seen anyone do that. But then, I'm not in your area.

The general rule is ducts first, then plumbing, wiring last. That's simply because the HVAC returns and runs take up the most space and can't be rerouted the way plumbing can. Furthermore, there is always some boxing necessary for the runs--at least on a two storey home--plus complementary boxes if necessary.

The preference in tracts is to use temp. heaters for drywall. That's because if the furnace gets fouled up with dust, the furnace suppliers won't honour their warranty. Last time I needed heat for drywalling, I used propane and the heat from several gas fireplaces. For the taping, I used the permanent system, first making sure there was a 5 inch filter in-line, plus a standard one-month filter.

Ducts, plumbing, electrical, phone/cable.
Worthy has it exactly right.
Big and hard to move first (a single extra turn in a duct system changes the flow), then plumbing since it requires drain lines that are 3 and 4 inches in diameter, then electric since it can be run pretty much as required around obstructions, then the phone, cable and other small wires since they are even easier to route.
Some plastic bags and tape will cover the openings between installation and final fit out with grates, etc.
I routinely just cut off the plastic and leave the tape on the sides of the duct hidden in the wall.

If you actually put up drywall before ducts you would end up tearing out huge amounts of drywall to get the ducts run.
The alternative would be a high pressure system like Unico that is much more expensive.

This is the order we went with.

Beginning of plumbing, most of electric, HVAC initial installation, that's ducts and stuff in attic, water lines, etc. for HVAC,finalized plubming and electrical, then spray foam, other insulation, then drywall. Hope this helps. DH did all the plumbing and electric so it was easy for him to plan the entire layout with the HVAC people so there was no problems in who laid what where!!

I do not live in a very cold climate so I'm not sure about what temperature has to do with it. It's been 30 and rainy here and DH is installing the drywall with no prolems, except his feet are cold. LOL

cheme

For general info on the pricipal of operation and studies on the economies - general seraches on line provided most of that data. But most of that stuff is accademic. Most of what I have learned is watching my installers and asking a ton of questions.

The biggest lesson I learned is that all of the economic data that is generalized did not apply to my specific installation. My cost to install was much higher than what the books say - and that was due to the great creator of earth, fire, and water.

The geothermal heat pumps are comparable in price to high efficiency heat pumps. The GT units might be a little more - but the cost delta on the hardware is so small that I would not make a decison on that part of the equation.

The biggest cost delta is the loop field or wells, loops, and pumps. And that is a huge unkwown when you start a project - especially if you are building in difficult terrain like we did.

My house required 12 tons of HVAC and was spec'd for one 6 ton unit and two 3 ton units. The extra cost to take the basic system (which would have been HE propane gas heaters and and electric A/C ) was $15,000 - not bad and in line with what the books say.

Then came the loop field. The huge 120' by 48' x 6' swimming pool that had to be dug. My contractor told me the pit would cost $2500 to excavate. He was off by a factor of 7!!! This is not typical - but it was reality for me. We hit a lot of diggable but HUGE rocks and my contractor forgot the cost to move a mountain of dirt from point A to point B and back to point A again.

In the end - I wanted geothermal and that is what I got. I wasn't going to let a few 4 ton boulders stop me. But if you are on the edge of the cost/benefit curve - then you really have to nail down the honest to god costs for the system. You cannot go by what the books say - you need to have an honest GT expert give you a real estimate for the system and site work based on your house and site conditions. Then you should add 20% on top of that to be safe.

I also would look at how long you are going to stay in the house. If it is a long time - the dream home - then go for it. But if your plan is short term - think twice.

I would also consider using a better insultation package (like foam) combined with HE natural gas or propane heaters or regular HE heat pumps. The cost of these combo's were - in the end - about what I paid for the GT system with a blown cellulose insulation package. However - the risks for me would have been a lot lower NOT going with geothermal. My excavation costs could have easily been another 2 to 3 times higher if we had hit a rock shelf that required a ram hoe to break up. Luckily for me - all the boulders could be scooped out with a humungous machine - no blasting or chipping required. I was happy to escape with the cost that we ended up with.

I love the GT - I am glad I got it in. It really does work and I expect my bills to be in the 125 to 200 dollar range throughout most of the year, during extreme conditions it might go up to 250. I have not had a steady state month in the house yet - but I plan to post the results in a few months. My expectation is that it will cost me no more than what I paid in my last home - which was half the size - and I think we will easily meet that goal. But it will probably take me 10 years, maybe more, to break even. And that's OK with me.

If you have specific questions, post them.

Best of luck.