Steam heat with mini-splits to whole house HVAC

pbekker · July 2019

Hello, I've got a ~1700 sq foot 100 year old house in Boston area with steam radiators for heating. From the bottom up: unfinished basement below that's 7 feet high, first floor has kitchen/living/dining/one bath, second floor has 3 beds/1 bath, 3d floor has one finished room (including radiator). We enjoy the steam heat but have never loved the big bulky radiators and there's huge variations throughout the house -- eg. bedroom toasty, dining room cold. We also like the mini-splits for A/C, but would like a few more rooms to be covered by A/C for those hot summer days. Meh...in the end this was basically livable for us. BUT THEN, came the basement refinish idea. That's when I realized, before I finish this basement, if I'm every going to change out this heating system, now is the time. And if I'm ever going to air condition more space, now's the time. After much consideration, what I'm thinking is as follows (BTW I have natural gas going to Burnham steam boiler right now).
- Change to HW boiler, wall mounted, and heat first floor with either retro-fitted in-floor radiant heat installed from below or regular slantfin/runtal radiators. (Navien combi here?)
- Air condition first floor with the existing mitsubishi 2-1 minisplits I have (this would require one head to be moved from second floor bedroom to first floor dining).
- Hydro-Air air handler (or heat pump?) in unfinished attic space to provide heating and cooling via newly installed ducts to second and third floors. (I just now heard of SpacePak...what about this?).

Would love the feedback, criticism, etc. of this plan...

Jamie Hall · July 2019

Hey, it's like they say down on 10th Avenue -- "If you got the money, honey, I've got the time".

At least your approach has the advantage of not adding a lot of duct work.

Steamhead · July 2019

pbekker said:
We enjoy the steam heat but have never loved the big bulky radiators and there's huge variations throughout the house -- eg. bedroom toasty, dining room cold.

That's fixable, for a lot less money than tearing everything out and putting in a whole new system. If someone tells you otherwise, they just want to take your money- show them the door.

For your 2nd and 3rd floor A/C, mini-duct systems such as Unico or Space-Pak will work very well. The higher air velocity makes you feel cooler at higher temperatures, which saves electricity.

pbekker · August 2019

Thanks Steamhead for taking the time to respond. Another note about the variability...The worst of it is the dining room which had an extension added on to it that's almost all glass. Massive heat loss, not accounted for by original radiator. Also keep in mind another goal is to clear headspace in the basement...steam down there reduce usable square footage...

Steamhead · August 2019

One of my Dead Men's Books says it's possible to run a steam main without pitch, as long as every runout comes off the bottom to act as a drip. I've never tried it but it seems like a good fit for your situation.

And a larger rad in that dining room will keep it warm.

Trust me- you'll HATE forced-air heat.

Jamie Hall · August 2019

Reading between the lines here, what I think I'm seeing is that @pbekker doesn't like the steam radiators, and doesn't like the lost headroom in the basement -- though I would point out that even without the pipes, the 7 foot headroom in the basement is not regarded as normally usable space.

The imbalance in the dining room can be fixed -- as @Steamhead noted and I implied -- at considerably less expense than replacing the steam with forced air. You may need more radiation in there, but I would start by ensuring that all that glass is properly insulated and insulating.. Remedying the other imbalance problems is usually pretty straightforward, although it may take some patience to get the venting right.

Steam heat with mini-splits to whole house HVAC

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