Cast iron, baseboard, radiant floor, and indirect from one boiler?

arctic_colors

I'm buying a house with an oil boiler (and electric water heater) and intend to convert to natural gas immediately. The heating system currently has two zones, one for baseboard in the basement and one for cast iron radiators on the first/second floor (old house so I assume converted from steam).

When we do the oil-to-gas switch I want to make sure the system is as efficient as possible, which seems to mean mod/con boiler and indirect water heater. There are a handful of other changes I'd like to make if possible:

• We have to gut and renovate a bathroom, and I'd like to replace the cast iron radiator in that room with radiant floor heating as part of that (I've wanted toasty bathroom floors since I learned as a kid that they exist).
• If it's feasible with the plumbing I'd like to split the first/second floor into separate zones (or even split it up by room by room with radiator valves).
• A bit down the road, I'd like to insulate and heat the garage, either with one of those hanging heater units with a fan or with radiant heating from the floor (since I might have to redo the concrete in there anyway).

My question is….how do I think about all of this? Do I have the right concept in mind (one properly-sized efficient boiler, with a bunch of stuff running off of it)? Will I need the primary/secondary piping loops I keep reading about? Are there any boiler brands I should prefer or avoid? And how do I find a contractor I can trust to do a good job and confirm that they'll do a proper installation, not one that the internet will laugh at if I post a picture of it 5 years down the road when trying to figure out why my boiler needs an early replacement?

My main goal is to spend the money now (judiciously, not wastefully) to minimize costs in the long run.

Just for reference, here is what the boiler looks like now.

Jamie Hall

Most likely NOT converted from steam. That would have been a difficult job.

OK. Having said that. Yes, what you want to do is feasible. However… there are some interesting complications which will require some thought.

You will definitely need primary/secondary piping. No question at all. You will then have what amounts to four zones: upper floor, lower floor, bathroom, indirect. The upper and lower floor zones will need water at more or less the same temperature, and that temperature, for best efficiency, can be controlled by controlling the primary loop temperature coming from the mod/con boiler, using outdoor reset (possibly with thermostats to trim if needed). The radiant floor will be a separate zone with its own pump and mixing valve, but is much too small to be allowed to control the boiler. The indirect will, of course, have its own pump and zone, and control the boiler as it needs to create the hot water (overrides the outdoor reset).

Now the garage. Two aspects to that. First, how far down the road is "down the road"? If it's within the next five years or so, you should at least consider adding its heating load to the new boiler. If it's longer than that, you may want to size the boiler for the existing load, and plan to replace it when you actually do the garage, since the new house boiler will be at md-life by then anyway. Using a fan forced heater is a good idea — but they take a higher water temperature than your house radiators will be using much of the time. This may alter the control and pumping strategy for the house. A radiant floor sounds nice — but unless you plan to take out the existing slab and insulate, it's unlikely that there is enough insulation under that slab to make a radiant floor a good choice.

Just some thoughts…

Kaos

My $0.02. Live in the house as is for a year. I can guarantee you there will be other issues you'll also want to fix, easier to do it all at once, no need to jump into boiler replacement if not at end of life. Yes, bit more expensive but that is noise compared to the work you are proposing.

On a pumped setup, you can replace a rad with staple up floor heat. This can be bare pipe or pipe with something like ultrafin. Either will work with the same temperature water as your rads. You can install a local zone valve and thermostat to drive it if you want more control. No need for a dedicated low temperature loop and pumps/controls.

Boiler guys like installing indirects. They are actually not that efficient even when connected to a modcon. Winter time efficiency is not terrible if the house heat is already running but even there it might at most be 85% efficient because the return water temperature is very high. Summer efficiency is much worse as you have to bring the boiler and associated piping up to temp each time the water tank needs heat, since there is nowhere to purge this heat once the tank is satisfied, all that heat is lost (which also adds to your cooling load).

If you want cheap hot water, get a regular power vented tank or tankless units. Material cost is less and they are simpler to install. Plus if your boiler goes down, you still have hot water. Some places offer significant rebates on heat pump water heaters, these are also a great option especially in a boiler room where there is extra heat in the winter.

Jamie Hall

A word about infloor — radiant heat. There is a very definite limit to how much heat you can get out of it. For the bath, probably if it's basically interior — but for the rest of the house, do a heat loss calculation before you even think about it.

EBEBRATT-Ed

Not converted from steam always hot water. Most of the pipe is copper and it is to small to ever have been used on steam.

arctic_colors

Thanks guys!

I figured it was converted from steam because the house is ~80 years old and I (apparently ignorantly) assumed that all old houses in NJ with cast iron radiators were built with steam, I guess because that's what I grew up with.

@Jamie Hall Thanks — for sure I will have a heat loss calculation done. Just trying to learn as much as I can before getting rolling, both out of curiosity and with the hope that it will help me hire a good contractor to do this stuff. Garage heat would be in the next year or two. With a modulating boiler, is oversizing not that big a deal (e.g. doesn't adversely impact boiler lifespan or efficiency, at least not too much)?

@Kaos I appreciate your perspective — we do want to put in a gas boiler right away so we can get rid of the oil tank ASAP (smells bad and wastes a closet in the basement), and we'll have a plumber setting us up for a gas range, grill, and dryer anyway. Wasted heat in the summer isn't something I considered. A few boilers/tanks I've looked at say they'd run the pump for a minute or so after the call from the water heater stops — presumably something like that plus some insulation helps? I was also thinking indirect because tankless units seem to get more complaints, and non-indirect tanks I thought require more maintenance & don't last as long or heat as fast (seems like indirects tend to have much higher BTU ratings).

Never heard of staple-up floor heat so will have to look into/ask about that as well.

EzzyT

@arctic_colors where in nj are you located?

We just did a project where we converted from our to gas with a new boiler and repiped the all of the piping in the basement with a home run set with a manifold station. The system was a an old gravity system with some rework done to it in the pass that caused uneven heating from the 1st floor to the 2nd floor. No with the current set up every radiator and baseboard in the house gets the exact same temperature of water supplied to it and even heating across the entire house. Here is a picture of the mechanical room.

HVACNUT

Its likely the first/second floor zone is a Monoflo loop, and can be made into 2 seperate zones the way @EzzyT described.

The second floor radiant bathroom must also be an dedicated zone. It cannot be part of the second floor zone.