Steam boiler Replacement, Heating system overhaul

mpitt

Good day. 

I have a house in eastern Canada, currently on a 2 pipe steam system and the boiler is reaching the end of its life. It's a oil fired slant Fin LD 40 with Riello 40 burner. 189 gross btu, 142 net.
The house is about 3000sqft with convection style Fin rads. The house is 90 years old. 

Many efficiency upgrades have been made to the house and it seems to hold heat reasonably well for its age. Currently, daytime highs are around 32f with overnight lows around 20f. The house is kept at 66f during the day and the total furnace run time is about 2.5-3.5 hours per 24 hour window. I believe it is now considered oversized for the heating requirements. 

I hope to gain some guidance for future planning. Moving forward we have a couple things to consider. We do not have natural gas as an option, we have oil, propane andor electric. There are incentives to moving off oil and into a cold weather heat pump system. During our home inspection, the inspector thought a central air handler in the attic would be a good option with ducting run to both floors (there is access from attic to main floor ceilings through knee wall attic space on second story). 

I feel this would be a good option but wonder about being leaving out the steam system. Is there an option to have a hybrid system that might compliment each other? 

offdutytech

The first thing you should do is get a load calc done on the home to determine the correct size of equipment you need for the home. Compare that with the current steam boiler to figure out if it's been oversized.
Once that's done you can figure out if you want to keep the steam system. Adding ductwork to a two a two story home and ditching the steam is going to be costly vs just replacing the boiler. If your goal is to AC you have a few options. 
1. Space pack unit 
2. Mini Splits 
3. Total system change out to forced air.

Perhaps one of the better options would be to replace the current boiler and add mini splits. The mini splits would give you AC and can be used as a heat pump for the mild shoulder weather when there is a light heating load during mild weather. It also gives you back-up heat should there be an issue with the oil boiler. You may get some incentives with the mini split in your area. It would also allow you to replace the equipment in phases. First mini split and second boiler. I have had a few customers with steam boilers do this and they have been happy with the results. When it comes to steam find a reputable and competent contractor who knows steam if you go that route.

mpitt

That's great information, I really appreciate it. I think it's along the lines of what I was thinking. I would be sad to lose the steam heat. It's such a nice warm heat. I've had forced air in previous homes and really never loved the dry air being pushed around. I agree the ducting would be a pain and if we wanted to keep the steam it would be a lot to have a new furnace and a full air handler, ducting combo. Sounds expensive. 

JUGHNE

IMO, adding ductwork in a cold attic that connects to grills in the heated space invites heat loss.

True the duct is insulated but that R value is so much less than the ceiling insulation. And your warm heated air will gravitate up into the cold duct.

Every hole you punch in the envelope invites heat loss by infiltration.
I would avoid an attic system if at all possible.

mpitt

That makes sense. I'd imagine that convection would pull alot of heat into the unconditioned attic space. As it is now, we go to bed and the house is about 66F and with the furnace off all night (930pm to 6am) the temperature when we wake up is 60f/61f. So with it being 20F outside overnight, I feel like the house does well holding its heat.

We could probably have a couple mini splits to help the shoulder seasons and give a little bit of AC in the summer. We typically don't have long stretches of feeling overheated without AC at the moment, but it would be nice for about 2 or 3 weeks that humidity and heat increase. 

Hot_water_fan

I like the centrally ducted solution much more than ductless minisplits - it’s generally much more efficient to have one outdoor unit connected to one indoor unit, as opposed to one outdoor unit connected to many indoor units. In addition, you’ll change the filter of a centrally ducted unit, ductless units will be ignored. Last, it’s easy to incorporate a backup heat source in the ducted unit (although you can keep the existing steam anyway, no harm there). Even in Canada, you’ll find that you can use heat pumps potentially the entire winter. There aren’t really shoulder seasons, more like shoulder days/hours. A day with a high of 32F is nothing for a modern heat pump. 

A well sized heat pump/furnace with a variable speed blower is comfortable. I find them more comfortable than hot water or steam but that’s subjective of course. You’ll have both in this scenario so you can decide for yourself. 

ethicalpaul

You can definitely keep your steam. If your current radiation is oversized, I see no harm in going with a smaller boiler than your current EDR...the boiler doesn't know how big your radiators are until they are all full and can no longer radiate what the boiler is making.

Steamhead

@mpitt , how hot does it get there? Do you really need A/C?

mpitt

Most of the summer would be 70-80F but there are stretches of 85F that can feel like 95F with the humidity. Traditionally AC is a rare occurrence, a luxury. I see more and more mini spits and people enjoy the AC aspect during a heat wave. Federal government have good programs and alot of people have come off oil in favor of mini splits, but with a medium/larger house I don't think I could/would get enough out of a heat pump like application. Perhaps a blend. 

Steamhead

Up there, that would indeed be a luxury. In Baltimore we get 95°/95% days for something like two weeks of the summer. If that were my house, I'd forego A/C.

mpitt

@ethicalpaul thanks. My steam set up just has to be oversized. The pressure control was set quite high 7psi with diff at 5psi when we moved in. So it would just pressure up to 6-7psi, hold that for a long, long cycles.... Once I lowered it to 1psi with diff at 2psi (operating now between 1-3psi) the system ran much better, but the cycles are short (3 min on, 2 off). House heats up great though 

pecmsg

You can’t warm wet winter clothes with a heat pump!

mpitt

I cant with my current set up either because the convection rads are build into the walls, lol

mpitt

mpitt

mpitt

A snapshot of our average temp up here. 

Jamie Hall

Your cycle times tell me your boiler is oversize, so you could -- and in my view, should, when you need to -- replace it with a smaller steam boiler -- as a first cut, based on cycle time, somewhere around 350 square feet of radiation (84,000 BTUh net power). They're out there. Better would be to add up the EDR values of those convectors -- someone else on the Wall may be able to help you with that.

Then if you want to and there are large rebates or subsidies to make the costs add up, you could consider adding a ducted heat pump, partly for the "shoulder" times or seasons, but more for the air conditioning. Otherwise, honestly, I'd skip the A/C... but I'm more familiar with Cape Breton and Truro than I am Halifax.

Oh and you can set your pressures even lower without hurting anything -- 1 psi cutin and 1 psi differential should work just fine.

pecmsg

mpitt said:

Small hooks and hangers 🤣

just like Christmas stockings!

mpitt

@Jamie Hall thanks Jamie. It might be slightly more mild than Truro or CB. Not a lot though. 
I do feel I have good attic space and this is what the it looks like behind the 2 floor knee wall. This runs the full length of the house on the front and back. 

ethicalpaul

A mini split will turn any uncomfortable summer day into a lovely day. Even if you just put a single head in your main living space, the difference is incredible. I had a "through the wall" unit and window shakers in my steam-heated house, and the mini split is way way way better.

Don't let people tell you it's not warm enough up there. I know you get hot days, and they aren't getting any cooler.

Hot_water_fan

@ethicalpaul I think that’s a great point - an AC system isn’t for the last decade, it’s for the next few decades. 

mpitt

I agree, the few weeks that coastal humidity and heat increases, it can be quite uncomfortable. Oil is rather expensive so a full retro or supplement may be beneficial too. 
 Oil is currently $1.60 canadian per litre ($4.50 USD per US gallon). 

Hot_water_fan

There’s also not a real deadline here: you can install AC via a heat pump, then wait a winter and decide if the boiler needs to be replaced. 

mpitt

Totally agree. I'd love to know about a possible steam boiler Replacement. Ill Do the numbers but I feel like something closer to 80-100k net btu would be more than enough, especially if I end up adding a few mini split zones. Curious is an oil to propane option is on the table or redundant? 
Anyone recommend a CI stean boiler i. That range? 

Jamie Hall

Remember that on sizing a steam boiler, it is done by the amount of radiation it powers -- not by the heat loss of the structure. I suspect your range is right, but without knowing the actual amount of connected radiation, it's a guess -- and adding the mini split zones has nothing at all to do with it.

Oil vs. propane? Which tends to be more expensive in your area -- per BTU, not per gallon! Oil has almost half again as many BTU per gallon as propane does.

mpitt

Oh good question. I think propane is slightly lower $ per BTU but probably not a significant amount. 

mpitt

There are 13 radiators, all 3 row fin style conveyors built into the wall. About 6 inches in depth.
Approximately 480" in total length . I'm not sure if that helps. They are all about 3' in width

mpitt

https://forum.heatinghelp.com/discussion/141877/trying-to-identify-and-rate-this-convector

It looks like I have something quite similar to this unit. Same height and depth but the length varies a bit.  It looks close to one sqft of radiation per inch of measured length. I guess this would put me close to 480 required square feet of radiation? I read that part of the problem with fin convectors is that they heat up quick, but shed heat quickly contributing to short cycling. 

mpitt

As far as oil vs propane. I read that:
138,000 BTU per gallon for #2 oil
91,000 BTU per gallon for propane

Our current price for propane is $3.78 per gallon. Oil at $6 per gallon. 

So propane would be $4.15 per 100,000btus

Oil would be $4.34 per 100,000 BTU. 

Not much in it, but propane would be a little quieter which would be nice...and it is cheaper