Sun Room- Add Sixth Baseboard Hotwater Zone or a Mini Split

stevetars · September 7

Hey everyone,

I recently switched to baseboard hot water and did away with the heat component of my forced hot air system. We added five zones and love it. We are now going to remove the entire forced hot air system (AC) and seal ducts, moving to Mitsubishi ductless mini splits (two dual zone condensers on either side of house and four heads). I am posting this here because we are at a crossroads. The HVAC tech recommended adding a fifth head in the sunroom which is currently on a concrete slab over a crawl space and attached to our dining room. It is a three season room with electric baseboard heat for winter. He said why not do a tri-zone condenser and add a fifth head for heating and cooling in sunroom. But, when I had the baseboard hot water system installed I had a vacant sixth zone installed so I could one day heat the sunroom. I'm not sure if I should run baseboard into the sunroom and add a thermostat and sixth zone or if I should do a ductless mini-split. After getting estimates, the price point is almost the same of each approach with ductless mini spit slightly higher. Here are my main considerations:

Will the baseboard in the sunroom present a major freeze risk if I ever lose power? Can this be prevented so I never have to worry about freeze risk?
Is the ductless mini-split a better option because it has cooling too?
The baseboard hydronic heat is steadier and better heat
Baseboard heat will last much much longer than the 10-15 year lifespan of a ductless mini-split
Pipe routing is pretty easy and zone is already set up
We are installing ductless mini-splits so adding another is easy and can be done as part of the larger job.

Any insight would be much appreciated. Really not sure which direction to go yet. Let me know if any more info is needed to help.

Thank you

pecmsg · September 7

Where is this home located?

stevetars · September 7

NJ- so we do get colder winters.

pecmsg · September 7

Im confused

You're eliminating the HW forced air but keeping the baseboard?

In not a fan of 100% mini heat pumps, too man y things to go wrong and parts are NOT readely available.

Keep the HW heating as a backup.

stevetars · September 7

My mistake- let me clarify. So we are keeping baseboard mutlizone throughout the house (gas hot water heat). We are installing mini-splits solely for AC, but since they come with heat pumps the HVAC contractor recommended adding one to the sunroom for its dual capacity- heat and cool, and eliminating baseboard electric. Prior to this recommendation, I was planning on just extending baseboard hot water (copper solder) into the sunroom. But now, I am unsure which direction to move, since the mini-split would eliminate any freezing risk-

pecmsg · September 7

Jamie Hall · September 7

I'd run the baseboard into the sun room — but on its own zone, as sun room heat demands are so different from other rooms.

As to freezing — unless that room is isolated from the rest of the house (doesn't sound like it) it's not much more likely to freeze than the rest of the house!

stevetars · September 7

Thanks Jamie- that is what I was originally planning until one plumbing contractor said he'd recommend just doing the mini-splits. I figured the hydronic heat would be better in the sunroom and in all honesty the room does not get too unbearable heat-wise, so we are not too in need of cooling. The room has two doors leading into it, which we may widen- so we can always open them to make it even more connected. We would definitely do its own zone.

pecmsg · September 7

Please don’t listen to that plumber.
keep the HW for when single digits and that NW wind blows.

EBEBRATT-Ed · September 7

If the sun room is open to the rest of the house and well insulated do the HW basboard.

If it is not well insulated and is basically a converted porch use the minisplits and keep the electric baseboard and set the baseboard stat set low like 55 deg, unless the minis can' keep up

stevetars · September 7

Sounds good- thank you everyone. The sunroom is over a crawl space, which connects to the basement proper. It does have wall to wall windows which are pretty drafty, but the floor is a concrete slab with two doors open to kitchen and dining room. Walls are and door are solid. I have to double check with a contractor to see about level of insulation in walls. Hard to tell. Right now, I am leaning towards baseboard.

hot_rod · September 7

did you run a load calc on the sunroom?

Wall to wall glass can be a tough space to heat

EBEBRATT-Ed · September 7

If you have a lot of glass baseboard is the way to heat it be it electric baseboard or hot water baseboard. Mini splits will not do the job. In fact I would go as far as to say baseboard is the only way.

I had an office building once where one wall was glass blocks. The room was unusable in the winter you could almost see your breath. It was never comfortable and had gas fired roof top units with overhead diffusers.

You could set the stat at 74 and as soon as the unit satisfied it felt cold due to the glass block wall which was like touching an ice cube.

I am sure some architect was pleased with his design.

The glass blocks were from floor to ceiling so no place for baseboard. We hired a Carpenter to build us a wood step at the bottom of the block wall and build a chase up the wall in the corner. We installed 20' of high output baseboard against the front of the step which had a removeable top to install the pipe. Problem solved

stevetars · September 8

That's a good point- it's Demi-walls all the way around with large glass windows. Still need to do a load calc, which we will do before we run baseboard. Yeah- this has me thinking baseboard is the right move. I also know baseboard well and the type of radiant heat it generates- really never have used a mini-split for heat. I'll probably also have the plumber put in a drain/shutoff valve beneath the junction point where the copper piping enters the sunroom underneath so in worst case scenario I can winterize if I had to.

hot_rod · September 8

I sure like the looks of panel rads in a glass sunroom. You still get the radiant output and feel but no need to build an enclosure. I have seen them right in front of glass walls where the glass is ceiling to floor.

The load calc is crucial if you want to warm this space to a comfortable condition.

Screenshot 2025-09-08 at 10.34.42 AM.png

Sun Room- Add Sixth Baseboard Hotwater Zone or a Mini Split

Comments

Categories