Adding hvac to an addition

[toohott7718]

Hello I am going to be building an addition on the back side of my house. I plan on building the shell like a pole barn would be framed then pour a floating concrete pad. As far as the hvac and plumbing I was thinking of running everything under ground then cut an access hole in the foundation and seal around the pipes. I have done a lot of searching and seen this done many ways. What is the best way I can do this? Thank you for any input

 

[LS6 Tommy]

I mean no disrespect towards whomever does the HVAC work, but personally, I wouldn't run any of the lines in or under a slab. No matter how good the man is doing the lineset, there is always the risk of future leaks. You don't want to be ripping up concrete to make repairs.

Tommy

 

[toohott7718]

The hvac duct will be extended from the existing trunk line, so no line set will be under concrete. This addition hvac will be supplied from the current house hvac system.

 

[LS6 Tommy]

You can't just "add" to an HVAC system. It has to have the capacity and airflow needed for the additional load.

Tommy

 

[toohott7718]

Sorry I should have included I am updating my air handler and condenser, Also going to be changing the trunk line for the additional load

 

[brewchief]

I'm no fan of underground ductwork but if done it needs to be done properly, there is coated duct designed for this use and a lot of care needs to be taken to make sure all the joints are sealed properly.

If you have a high water table the ductwork can turn into a drain tile pretty quickly, we had a system this spring that we had to run all new duct through the attic and abandon the underslab duct, it had a sump pump in the ductwork because it took on ao much water.

Sent from my SM-G900V using Tapatalk

 

[theoldwizard1]

Hello I am going to be building an addition on the back side of my house. I plan on building the shell like a pole barn would be framed then pour a floating concrete pad.

First, update your profile with your location.

Check your local building codes ! That won't fly in many parts of the country.

As far as the hvac and plumbing I was thinking of running everything under ground then cut an access hole in the foundation and seal around the pipes. I have done a lot of searching and seen this done many ways. What is the best way I can do this?

Heating and cooling an addition is always a challenge. The simple solution is install a mini-split heat pump. They are perfect for heat and cooling a 1-3 room addition and are very efficient.

Yes, it will cost more to install, but you will be a lot more comfortable. (I lived in a house where the addition was cold 6 months a year, so you had to use an auxiliary electric heater. That really ran up the electric bills in winter !)

 

[toohott7718]

How do they normally seal the pipe when it goes through the foundation?

 

[toohott7718]

I'm still not sure what I want to do, I just want to know how it's done so if I do have it done that way I know it's done right. Another hvac guy suggested that we cut holes in the band board and run 2 vents there on the wall and leave all the plumbing in the ground.

 

[Fueler]

Listen to old wizard. You can't have ducts connecting the garage to the house. It's a code restriction most places and just common sense.

edit: Oh, you didn't say garage did you?

 

[toohott7718]

Listen to old wizard. You can't have ducts connecting the garage to the house. It's a code restriction most places and just common sense.

edit: Oh, you didn't say garage did you?

No ducts will be connecting to the garage to the house

 

[theoldwizard1]

I'll say it again .... Mini-split heat pump !

Easy to install
Works well

 

[rieferman]

I'll say it again .... Mini-split heat pump !

Easy to install
Works well

Firstly, when wizard speaks, I listen. His posts are on the money 99% of the time (probably more).

Secondly, +1 on the mini-split. They're efficient, cost effective to install, and would not impact your existing HVAC system. When I was selling construction, we used them many times - due to happy customers, I installed one in my barn... very happy. My folks put on a nice addition to their house and used one... very happy.

That said... if you're dead set on extending your existing system and all that comes with doing that, let us know and any additional replies should focus on that.

 

[Falcon67]

Another vote for mini-heat pump. Our main AC is sized to the house volume and is working well. Adding any sort of decent sq/ft other than a closet would put more load on the system than it was sized to handle. You can cripple the whole thing easily. We (the contractor on the replacement system) fixed a substantial imbalance in the volume to one bedroom by changing from a 7" to a 9" duct. It doesn't take much to really change the operating parameters of a typical AC system. Plus, the minis are very efficient and would probably add very little to the existing power bill.

 

[toohott7718]

I'll say it again .... Mini-split heat pump !

Easy to install
Works well

I would love to do a mini split heat pump if I had $1500.00 -$2000.00 extra laying around. Also if I was heading that direction, I would install dampers and have a multi zone system.

 

[volleyball]

We still don't know what kind of system you have currently and how much space it conditions. And if you can upgrade it, why not leave it alone and use that upgrade money towards a new system.
And what is the use and layout of the new space. Mini splits work in some locations but are terrible for others. Nobody can say for certain what will work when we don't know what we are working with.

 

[72Anthony]

Have you priced labor and materials for the underground ductwork?

 

[toohott7718]

We still don't know what kind of system you have currently and how much space it conditions. And if you can upgrade it, why not leave it alone and use that upgrade money towards a new system.
And what is the use and layout of the new space. Mini splits work in some locations but are terrible for others. Nobody can say for certain what will work when we don't know what we are working with.

The house is 1056 sq ft and we are adding a 16x12 room. The house has an air handler in the basement and the normal condenser outside. I believe we have a 2.5 ton condenser. I plan on updating the whole system. From what I was told the new addition should only an extra half ton of air so a 3 ton unit should be fine (what hvac guy said).

 

[toohott7718]

Have you priced labor and materials for the underground ductwork?

Very expensive, I really don't want to do it, I just want to know how it is done, and how well it works

 

[toohott7718]

No more suggestions?

 

[matt_i]

More info needed. I re-read your original post a few times. Do you have a crawlspace or basement where you are intending to knock out a block/cut hole in the existing concrete sidewall as an access point?

In my climate I would build any addition with 2x6 framing at minimum. 3 sides are going to be cold, heat-losing entities.

Relative to framing like a pole barn, I think you want something sealed against bugs and mice better than pole construction, like with a row or two of block (or poured) and framing set on that. Your local codes and building department may also have the same idea.

 

[fastjohnny]

I would love to do a mini split heat pump if I had $1500.00 -$2000.00 extra laying around. Also if I was heading that direction, I would install dampers and have a multi zone system.

And how much is updating your whole system with a bigger unit going to cost?

Another minisplit vote.

 

[volleyball]

No more suggestions?

No more suggestions until you answer ours and explain what you have.
You may know what you have but we don't. And any option when you don't know has already been given.