Converting three season to four season porch

Aberagejoemn

Im planning on converting my three season porch to a fully finished heated space in Minneapolis Minnesota.

Currently: The add on porch was added in the 60s or 70s. It sits on a concrete slab and is roughly 110 square feet.
Plan: Remove all the old crappy windows and install new ones probably 8 double hung in total. Spray foam the roof (it's a hip). Spray foam the outside walls. New tyvek and new siding. New electrical and a new exterior door. The current slab floor is sloped away from the house so we plan on putting a moisture barrier down and framing a sleeper floor on top of that with r-15 fiberglass batts, then plywood. This will allow us to level the floor with the rest of the house and raise the floor so it's even with the house.

My question: What is the best way to heat this? We have radiant steam heat in the rest of the house and trying to add a steam radiator seems really difficult given how finicky steam systems are. Also, considering we’d have to route a supply line through the concrete slab I’d assume we’d lose a lot of heat to the slab or have to elevate the radiator within the expansion (so it drains properly). We asked our contractor friend about electrical in floor heat and he said the slab would suck a lot of that heat out. He suggested a gas stove vented out the side. We also have a mini-split AC system - can we plug into the outside compressor to deliver AC to this room, but also get the wall unit that has a heat pump for winter? I’m assuming that we’d be then using electricity to heat which isn’t as cost effective… What else should we consider?
Thanks!

FranklinD

We did something similar on our house up near Duluth. Despite new Windows, an insulated floor, R-13 in the walls and R-30 in the roof, it is a tough room to heat. We finally just gave up on trying to heat it during the really cold parts of winter (we installed electric baseboard to see how feasible it was before investing in an extension of the hot water system - the baseboards actually do very well keeping it warm, it's just prohibitively expensive to heat all the time).

Granted, different situations...and I'd bet the spray foam would do better than standard FG. Our porch is NE facing and is subject to the wind directly off of Lake Superior. No real passive solar input. The room came out nice, and we use it probably 9 months out of the year, just not when it's below 0* for extended periods. With all those windows, if you're south/southwest facing, you may be surprised how much heat you pick up on sunny days.

You could run a hot water zone off of the steam boiler, but I'd find a way to keep steam out there if you could. That way, should you decide not to heat it, there's no risk of frozen pipes and broken radiators. If you go hot water, you're committing to heating it (unless you drain that zone and really blow the water out). Maybe a steam radiator on the ceiling? That would likely solve any real pipe pitch issues, and save floor space. And I always think they're really neat-looking when I see pictures of them

kcopp

If you can get a gas line out there I would try a Rinnai vented heater.
As to insulation on the slab... Fiberglass is a poor choice. I would place as many inches of Blue Dow board under the sleepers as you can....right up to he underside of the sub-floor.
I would also get a bit anal as to your air infiltration. Caulk and tape every joint and seam as you can.

njtommy

I wouldn't recommend install a hot water loop and tieing it into your steam boiler with out using a plate heat exchanger. The only reason I say this is you would have no freeze protection if you where to lose power for longer periods of time. If you used a plate heat exchanger you are able to use Glycol to protect you baseboards or cast irons rads which ever way you deside to go.

SWEI

I was part way through typing a similar response. There may be no need for sleepers if you can float the floor. XPS is available in custom cut tapers (typically 1/4" or 1/8" per foot, intended for use on roof and deck assemblies.) Build up a level plane and keep it all in compression.

Spray foam is not my favorite material. I'll skip the environmental health lecture for now (highly toxic materials, some of which are endocrine disruptors), but from a purely thermal performance standpoint you need to be aware of two critical facts about polyurethane (including polyiso) foams:

1. Their R-value begins degrading the day after they cure. The "initial R-value" you see quoted (typically R7 or 7.2 per inch) is actually measured some months after curing. The degradation continues essentially forever, even if they are kept completely dry.
   
2. Regardless of what the label says, these are not truly closed cell materials. When exposed to moisture long enough, they will become soggy. At that point, the R-value goes to approximately zero (and you have a fabulous medium on which to grow mold.)
   

EPS or XPS both represent far better choices for installation in potentially damp areas. Think roof assemblies and exterior walls -- especially the lower portions of walls.

lchmb

you could put a mini split in so you have both options (ac and heat) and then add a small Rinnai to off set in the extreme cold...just a thought. The newer mini splits are good to minus 13 degree's and extremely efficient. If you already have gas at the building the rinnai would be effective also...

SWEI

Overhead gas radiant?

Aberagejoemn

kcopp said:

If you can get a gas line out there I would try a Rinnai vented heater.
As to insulation on the slab... Fiberglass is a poor choice. I would place as many inches of Blue Dow board under the sleepers as you can....right up to he underside of the sub-floor.
I would also get a bit anal as to your air infiltration. Caulk and tape every joint and seam as you can.

Thanks, I'll definitely take the rigid foam advice for the floor - should my floor sleepers be 16 OC or 24 OC?

SWEI said:

I was part way through typing a similar response. There may be no need for sleepers if you can float the floor. XPS is available in custom cut tapers (typically 1/4" or 1/8" per foot, intended for use on roof and deck assemblies.) Build up a level plane and keep it all in compression.

Spray foam is not my favorite material. I'll skip the environmental health lecture for now (highly toxic materials, some of which are endocrine disruptors), but from a purely thermal performance standpoint you need to be aware of two critical facts about polyurethane (including polyiso) foams:

1. Their R-value begins degrading the day after they cure. The "initial R-value" you see quoted (typically R7 or 7.2 per inch) is actually measured some months after curing. The degradation continues essentially forever, even if they are kept completely dry.
   
2. Regardless of what the label says, these are not truly closed cell materials. When exposed to moisture long enough, they will become soggy. At that point, the R-value goes to approximately zero (and you have a fabulous medium on which to grow mold.)
   

EPS or XPS both represent far better choices for installation in potentially damp areas. Think roof assemblies and exterior walls -- especially the lower portions of walls.

I'm really torn between spray foam and either rockwool or ridigid foam (XPS as you mentioned). Problem is the porch has zero soffit venting:
http://imgur.com/a/fu2y4

Without venting I'd have to go hot roof, and typically that's done with spray foam.

Aberagejoemn

lchmb said:

you could put a mini split in so you have both options (ac and heat) and then add a small Rinnai to off set in the extreme cold...just a thought. The newer mini splits are good to minus 13 degree's and extremely efficient. If you already have gas at the building the rinnai would be effective also...

So I already have a minisplit system for cooling my upstairs, can I add a second unit and tie into the existing outdoor compressor (which is right by the porch) and save money that way?

http://imgur.com/a/fu2y4

SWEI

Open eaves inside, or is there a ceiling?

Is that darker gray horizontal bit at the bottom a protruding slab edge or some kind of trim board? I'd face the concrete using a minimum 2" of XPS -- 3" or 4" would be even better. Dig down at least a foot. Cut a 45° bevel at the top of the foam. Face the foam and bevel with cement board. Cut a kerf into the existing structure with a circular saw at an upward 45° angle so it lines up with the bevel. You can cut a wider kerf and insert the cement board directly into the kerf, or cut a narrow kerf and use a bit of flashing. Finish as desired -- stucco and stone both work well.

lchmb

So I already have a minisplit system for cooling my upstairs, can I add a second unit and tie into the existing outdoor compressor (which is right by the porch) and save money that way?

http://imgur.com/a/fu2y4

It all depends on the unit you have. If it has ports left and enough size. But a lot would depend on the unit also. Older unit's were not able to function at peak efficiency in below zero temps. May be more cost effective to purchase a complete new unit..

SWEI

Highly unlikely they installed a multi-split outdoor unit with only one indoor attached. Single splits cost less and have better low temperature heating performance.

The slab and roof insulation will be key to whatever heat source you choose.

lchmb

actually SWEI I've done it a number of times. The newer units are much more efficient even with multiple indoor units. They do however cost a bit more up front..

Steamhead

When you remove all the crappy windows, you can leave enough height when sizing and installing the new ones so you can use cast-iron radiators and still have the steam pipe pitch back toward the house. This would be the simplest way to do it.

vaporvac

I'm not understanding the issue with running steam to this addition. For a solarium I can testify it's ideal. Perhaps a schematic could help folks figure out a work around.

John Mills_5

You have to have a mini split outdoor unit designed for multiple heads and it has to be a heat pump.

JUGHNE

And being in Minneapolis, you will need back up heat installed for that room. Regardless of the claims of any Minisplit system. They won't cut it in northern NE, (I've put in more than a dozen here and we know you still need back up heat).

If your existing minisplit has multiple head for AC, that would be good for your room.

Steam would sure feel good in your winters.

Aberagejoemn

Here's the side of the ac mini split compressor: http://imgur.com/a/5bJYg

Does the wall unit produce heat or is it related to the outside compressor? My thought was the compressor is only for ac...?

JUGHNE

That looks to be AC cooling only, a single 9000BTUH inside coil. That is all it is ever going to be. That is 3/4 ton of cooling, probably takes the edge off for your second floor. Usually the smallest anyone makes.

You could get that size in a heat pump/AC for your new room. It would heat well in the "shoulder" seasons. But when the steam came on for the house and your pants were ironed by just standing by a cast iron radiator and you go put your hand in the lukewarm air of that heat pump,, you will probably shut the mini off and enjoy the steam. That is the good thing about heat pumps, (even high temp minisplits).......you really appreciate the real heat of steam or CI hot water radiators. It is like fasting with only drool for a week and suddenly having a real meal!

I grew up with a frozen glass of water next to me in the morning.
Margarine instead of butter etc.......so now the simple things are really appreciated. And I had it so much better than the previous generation.....they all talked about the fact that they all wanted to be warm...not to have to chip ice etc. But digressing..

Fred

@JUGHNE , I remember walking to school in 2 feet of snow, uphill, both ways.

BobC

@Fred While it was sleeting!

Fred

BobC said:

@Fred While it was sleeting!

You're right!
EDIT: And we all know we had to do it bare footed. Who could afford shoes?

JUGHNE

It never got warm enough to sleet until about Easter!

But the frozen water glass is true, for the more dedicated Catholic kids even their Holy Water was frozen.

The Nuns tried to keep holy water in my room but it burst into flames, a little heat for a while anyway.....

Fred

OK that's Sacrilegious. LOL

JUGHNE

I earned these bragging rights......want to see the back side of my knuckles?

Fred

I had a 300 pound lit teacher, who, if you were talking or passing notes, would creep up behind your seat (as best as a 300 woman could creep) and stomp on your foot. Never waalked the same after that!

BobC

My senior year in HS the whole class went on a weekend retreat about 20 miles west. We got there Friday night had a little meeting to set the schedule and settled in for the night with our smuggled pints.

By the time we got to the Sunday morning mass one of our classmates had done a better than usual job of pissing us all off. On the way down to mass, we grabbed him, jammed him into the dumbwaiter, and went on our way. I pulled the motor fuse when the dumbwaiter was between floors and filed into the chapel like the good little angels we were.

As the priest was raising the chalice you could hear a distant plaintive voice - "Help, get me out of here". It took the priests abut 15 seconds to figure out what we had done and a good 10 minutes to find another cartridge fuse to replace the one in my pocket.

When we got back to that school the dean of students was royally pissed, that went down as the classic prank of our 4 years there.

Good times at Ridgemont high,

Bob

JUGHNE

Where were the child protective agencies at then???

But 6 years later Air Force boot camp/basic training was a breeze. They could not strike you there. And your childhood training kicked in and kept you out of trouble for 6 weeks. There were other guys without that experience who were crying at night in their bunks.

BobC

We had our drill sgt removed for striking a draftee in 1967 at Ft Jackson. We went without a drill sgt for 6 of the 8 week basic training cycle by policing ourselves.

The military was a great learning experience, I learned how to deal with people of all sorts during those 3 years. Society was probably better off when large numbers of young men for forced through that meat grinder, a lot of young toughs came out of it better than they went in.

Bob

JUGHNE

Well, the OP is probably hoping we take our meds and get parked in front of the "Gunsmoke" rerun in the solarium.

How close is the basement steam piping to your new room? Quite often more steam radiation was installed in rooms than needed. You are tightening up the envelope on that exposed wall. Perhaps there is a rad near the outside door going to new room, any chance it could be just relocated on the other side of the wall into the new room?

A floor plan of the adjoining room(s) and location of radiators, along with basement piping pictures could shed some new light on the possibility of using steam for this room. IMO