Slab Addition

[ANDYHD]

Hello, Looking for some advice. I have read the rules and I am not looking for DIY instructions just some insight. I spent my earlier years framing and roofing so I'm no stranger to construction and the trades but I also have learned quite a respect for trade professionals. I live in a small ranch (900SQ) and will soon be building a (400sq) small addition. I had a new downflow furnace and central air installed a few years ago and had it sized for the future addition. At the time a manual J was completed. The house is slab on a foundation wall SW PA. The addition will be the same. My major concern is extending the ductwork to the addition. Some questions I have

Should I go through the existing foundation and extend the two 8" ducts on that side? Will involve disturbing load bearing foundation wall

Should I all another duct at the furnace location (utility room) and take it through both attics? will involve cutting up slab and adding to plenum

Should I plan on adding room to room venting or additional cold air return? (currently one central return)

Any other advice you can think of? FYI the addition will be 2 bedrooms and insulated much better than the existing home.

The reason I am asking is I have contacted a few HVAC contractors and none seem interested right now. I have to have my footing, slab, and framing plans submitted within a few days to get on schedule. I appreciate any help and advice and I remind you that I will have a qualifyed HVAC tech install the ductwork I just need some ideas

Thanks
Andy

[skippedover]

Should I go through the existing foundation and extend the two 8" ducts on that side?

If the original duct layout was done properly, there is not enough air left in the existing trunks to just extend them further and expect any kind of performance or system balance.


Should I all another duct at the furnace location (utility room) and take it through both attics? will involve cutting up slab and adding to plenum

This could be a good option if you can install volume dampers in the existing trunks for you can balance the system. Otherwise, a zone system might be indicated.


Should I plan on adding room to room venting or additional cold air return? (currently one central return)

The return air should be balanced to the supply air. You state below there are bedrooms involved. If the bedroom doors will be closed, you should have a return in each bedroom balanced to the supply airflow. As to how that's achieved is up to the duct designer. There's really not a wrong way, just a preference.


Any other advice you can think of? FYI the addition will be 2 bedrooms and insulated much better than the existing home.

This could create an imbalance in the system that could prove to be uncomfortable. I'd recommend either a zoned system using dampers, designed with a proper relief strategy or at a minimum, volume dampers on the main trunks so they can be balanced.


The reason I am asking is I have contacted a few HVAC contractors and none seem interested right now. I have to have my footing, slab, and framing plans submitted within a few days to get on schedule. I appreciate any help and advice and I remind you that I will have a qualifyed HVAC tech install the ductwork I just need some ideas

Thanks
Andy


This is an unfortunate circumstance. A professional installation is the only really acceptable solution. Perhaps waiving a little more money in their faces will get them interested. :)

[ANDYHD]

If the original duct layout was done properly, there is not enough air left in the existing trunks to just extend them further and expect any kind of performance or system balance.

That was my biggest concern, If I had to pick the coldest outlets i the house those two would be them anyway. Well, That at least means I can submit my plans without ductwork in the concrete



This could be a good option if you can install volume dampers in the existing trunks for you can balance the system. Otherwise, a zone system might be indicated.


Is it possible to install without demolishing the entire floor?



This is an unfortunate circumstance. A professional installation is the only really acceptable solution. Perhaps waiving a little more money in their faces will get them interested. :)

Probably my fault, I feel obligated to tell the HVAC guys that they will look now, build later. Thats why hear "call me when your ready to get the ductwork, well figgr it out then"

Thanks
Andy

[ANDYHD]

OK, I had visits from three local HVAC companies and one more scheduled for Monday. We had a major break in the cold this past week and they were able to "fit me in"

Contractor 1 says it's a perimeter duct system, interrupt the perimeter and add about 40 feet to it allowing for three outlets in the addition. Also recommended addind an equal size air return in the addition and joining it to the eisting one.

Contractor 2 says to get a mini split system, does not install them but recommended another company that does.

Contractor 3 says use baseboard heaters and window unit AC and call it a day or install a complete new system (upflow) with all new attic ductwork and that includes major work to the existing home.

Contractor 4 coming Monday, very curious

Okay, 1 sounds great but almost too easy and cheap, I would love this option but I'm afraid of poor operation

Option 2 is okay, I really am not found of the looks of the ductless system but I hear they work fantastic and that they can be installed with decent warranties.

Option three, I'll buy a new house before spending that kind of money lol. Really I'm sure that will be out of my range.

BTW I turned down any ideas of hydronic in floor with Pex due to the lack of AC

I appreciate any opinions you have to help me make an educated choice. Please let me know your thoughts

[tinknocker service tech]

conventional ductless is a bit ugly to some people

sayno and a few others ave a wide verity of options for you to look into

you can get them that look like

picture frames
mirrors
hanging from the ceiling

i believe there are some that look like track lites
do some checking and you may find something you like

for 400sf a duct less heat pump is your best bang for you buck

[dash]

Contractor #1 may be right.

Since the addition will be better insulated,those rooms wil require less air flow then the rooms they are attached to.Plus the rooms they are attached to have now lost one outside wall/window,so they need less air flow then before.

A Manual J load calculation of the entire home,roo by room will tell.Then a Manual D duct design,will tell if existing ducts can be useed to serve the addition.


Here in Florida customers often enclose the rear porch into a Family Room,the outside wall that becomes an interior wall with the enclousure,had sliding glass dors and little insulation.Builiding the enclousure with super insulation and windows,plus adding insulation to the exsisting attic,often results in no increase in equipment size

[bmathews]

Its hard to tell a lot without a plan or walking the job. Where is the guy that installed it originally. Surely you told him your future plans and he had some vision in mind of what to do when the time came.

[ANDYHD]

Its hard to tell a lot without a plan or walking the job. Where is the guy that installed it originally. Surely you told him your future plans and he had some vision in mind of what to do when the time came.


I wish I could find him, Unfortunatley he was bought out (local family owned) buy a larger operation and I can't find out who I talked to, They have no recorde other than the install. They are unable to find any consultation. They were HVAC 4 on my list and will be here tomorrow for a consult.

As for the ductless heat pupm, will a heat pump function well in a PA winter?

I appreciate all the advice, I will post the results if tomorrows consult and then make a decision. One last thing, any preferences you all have for duct mayerial under slab? PVC or Plastic coated spiral.

Thanks

[dash]

"A Manual J load calculation of the entire home,roo by room will tell.Then a Manual D duct design,will tell if existing ducts can be useed to serve the addition."

The only way to know which way to go,find a contractor that will do it,IMHO.

[skippedover]

As for the ductless heat pupm, will a heat pump function well in a PA winter?


A heat pump will work anywhere, provided the proper load calculations are done and the proper size heat pump is selected. Sizing the HP as it would be sized for AC is huge mistake. The equipment must be sized for the actual heating load. For example, if the room need 10,000 Btu's of AC, it might need 22,000 Btu's for heating. Putting in a 12,000 Btu HP would leave you shivering mightily on a cold day. Even a 24,000 Btu HP would not carry the load unless it's capable of doing the 24,000 Btu's at your PA design temperature. Some manufacturer's give HP ratings at 17-degrees, which gives at least a good idea of what they'll NOT do at zero. So one possible solution, if necessary, would be two units, one used for cooling and both used for heating. Of course, there's considerable money to be spent for such a thing.

The contractor who noticed that you have a perimeter system sounds the most knowledgable but I woudn't accept anything anybody says until they've done a full Manual 'J', room-by-room for the whole house, determined what size furnace you need to do the job, how much air is needed in each room with the new addition figured in and then Manual 'D', is the existing duct satisfactory to add on to or does it need to be ripped out back to the source, the furnace, and start from scratch. Ducted systems properly installed do not easily lend themselve to being 'added' onto.

[ANDYHD]

Okay, after the last visit I now have a lot of faith in the last contractor and maybe not as much as the others. Looks as if I have a multiple loop not perimeter and nothing is zoned. The last tech took CFM readings at all outlets and found that tha back half of the house has terrible flow and is most likley leaking ducts under the concrete. The lowest reading was 48CFM for a 12X12 bedroom. This tech suggested upgrading to a 90+ upflow furnace, all new insulated ductwork installed in the attic, multiple air returns and making it a 2 zone system with the existing house one and the better insulated addition another. He said no more zones are needed if the ducts are sized properly per room.

Okay I am going to go with that plan to control energy costs in the long run. I am going to build the addition over the summer, and heat it through next winter with a few baseboard heaters and the nearby fireplace. I will get the new system n the early spring after that (financially I have to wait that long)

Without having a tech make 35 visits during the two bedroom addition I would like to leave provisions in the addition for the ductwork to be added. He noted that he would like two outlets in each room, both on the outside wall. Can I just install the outlet/register in both rooms and tape off in the attic until the following spring? each duct in the wall will be limited to a 2X4 wall cavity on 16" centers. Any recommend type of duct and register that is universal enough to be easily accepted almost 2 years from now? Size and type recommendations would be great. I asked him about desigining the whole house duct system now but he said for maximum efficiency I should wait until I pick out a system.

Well, thanks for the help thus far.
Andy

[ANDYHD]

Sorry, I can not edit the post. I meant that I have a lot of faith in this guy for actually bringing tools and measuring something, and maybe not as much in the others who spent 5 minutes in the house.

[cem-bsee]

be damm sure that the slab perimeter has insulation under it!
see BUILDINGSCIENCE.com

where is the hot air going that is under the existing concrete?
if there is a problem there, most likely:
air flow issue due to: crushed ducts, or just rough ducts which add friction to the flow.