Replacing house steam boiler with what??

stembo

Hi all, we have a 1-pipe steam system in our home in NJ, and are going to replace our old 150k btu steam boiler. The reasons to replace are we are renovating 1/2 the house so the steam system will be smaller, and we know the existing boiler is very poorly piped with a badly designed header. Since we are keeping the steam, is there anything more energy efficient than a basic steam boiler? Perhaps there is something like a hybrid system that uses a heat pump to heat the water initially, and then gas to make the jump to steam? Our goal, by the way, is to not only use less energy but also reduce the amount of natural gas we use. I don't see a lot of information out there, so any thoughts would be greatly appreciated.

Thanks,

Paul

Steamhead

Will the renovated half still have steam?

Jamie Hall

On the hybrid idea… um no, sorry. The physics is against you. That jump from a simmer at 212 F to steam is what powers the whole show — that's where you get the 1000 BTUh per pound of water. Getting it from medium condensate — say at 100 F or so — up to that simmer point only takes about 100 BTUh per pound. Even if you could get a heat pump to get there, it wouldn't be worth it — and there aren't any commercially available heat pumps which get much over 140, never mind 212.

@Steamhead 's question is essential. To rephrase, with what are you going to heat the renovated half? Unless it needs to be a completely separate heating system — such as might be for a separate apartment paying for their own utilities — there would be a lot to be said for rebuilding the steam system in that part to suit, and sizing the new boiler to fit the total load. I can think of at least two folks in New Jersey who could do that and do a beautiful job of it — at a wholly reasonable cost.

pecmsg

do the hybrid with the Steam for the cold windy nights.

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1808742#Comment_1808742

I think that what @pecmsg means here is to use a heat pump — minisplits, unless you want to install a lot of ducting — but not an air to water heat pump to boost the steam. And that would work, and is the way a number of people who can afford it are going.

Hot_water_fan

Do you have AC? You can install a ducted heat pump in that situation. It can be when the AC is already being replaced so it’s essentially free. The steam can remain as backup or you can remove it if you want. Your call, you know your own desires, we do not. As to your question about gas efficiency - a properly installed steam boiler doesn’t get more efficient when replaced with a new one. The most efficient boilers (hot water, not steam) are marginally more efficient than steam. A heat pump is substantially more efficient than a boiler, even when the electricity it uses comes from natural gas. We can show you the numbers if you wish.

Steamhead

@Hot_water_fan , I'd appreciate seeing those numbers. Do they take into account the fact that generating electricity from fossil fuels is something like 30% efficient by the time the power gets to your house?

Hot_water_fan

@Steamhead I’m pretty sure I’ve already shown you.
Let’s compare 1 MMbtu output to different amounts of gas input.

High efficiency gas: 1 MMBtu/95% = 1.05 MMbtu input.

Steam using gas: 1 MMbtu/85% = 1.18 MMbtu input.

HP powered 100% by gas in PJM:

1 MMBtu/3412 (BTUs/kwh) = 293 kWh. 293 kWh output / COP of 3 is ~ 100 kWh input. 100kwh / 50% (roughly gas combined cycle efficiency, as linked below) = 200 kWh. Back to MMbtu: .68MMbtu input.

I’m sure people will quibble over the numbers. This is a quick example, but it shows that a heat pump uses about 33% less gas than a high efficiency furnace or boiler for the same amount of heat. It’s not that close.

https://www.eia.gov/todayinenergy/detail.php?id=47556#:~:text=EIA%20separates%20combined%2Dcycle%20natural,kWh)%20in%20combined%2Dcycle%20mode

Steamhead

I think they're comparing the power being consumed at the point of use. No mention of generator/grid efficiencies.

Hot_water_fan

it’s a post. It’s not a dissertation!
For certain, my calc is isn’t precise. But the efficiency gap is real and wide - about a third less gas consumed. Some exclusions: a CI gas boiler will be less efficient in warmer temps - that’s excluded from my calc. A mod con may be less efficient at colder temps - excluded too. Electrical line losses (~5%) - excluded. Gas network losses - excluded! Non-gas generation (nuclear, wind, solar, coal) excluded! Future changes to the grid generation mix: excluded!

Most importantly - it’s not either or! You can use a CI boiler for cold temps when it’s most efficient and the HP for warmer temps when it does best. A HP provides AC. If that’s important, then the decision changes: it’s not HP vs gas it’s HP vs. HP+gas.

Jamie Hall

The real bottom line, @Hot_water_fan , is in your last sentence just above: ideally one would have available, and use, two sources: the heat pump in the range where it operates at a better efficiency overall, and also provide cooling the those who want that, while a fuel fired system — hot water or steam — would take over when either the heat pump's heating capacity was inadequate, having be sized for optimum performance at lower heat loads or for cooling, or when the two overall efficiencies crossed over.

That is the best solution. Unfortunately, there are two areas of difficulty for implementation. The first, and less obvious in the US so far but glaringly obvious for my cousins across the pond, is that regulations may not permit retaining the fuel fired heating source. This is leading to an awful lot of very chilly and damp houses…

The second is more real: actually determining the optimum size for both units requires more expertise than most folks are willing to apply — and worse, actually determining the optimum changeover point is fiendishly difficult — and with the variety of electrical generation available — borders on the impossible.

This leads me, at least, to the conclusion that if one has a fuel fired heating system in good condition, well maintained, it should be kept in operation to do the heavy lifting, with, if desired and if it is in the budget, a quality, though not necessarily ultra low temperature, heat pump to manage the "shoulder" demands and cooling.

Your mileage may vary — and my opinion may change as technology changes!

Hot_water_fan

ha @Jamie Hall lets be realistic - it’s going to be a furnace 95% of the time. Not steam or hot water. But otherwise sure.

Something to consider is the cost of the furnace. A furnace is cheap but also its utilization would be lower in a dual fuel application. Some reasonable people may decide it’s not worth having. That’s okay. The products I see the least rationale for in this scenario are the so-called high efficiency gas heaters. You’re trying to sell me something more expensive, barely more efficient, arguably more failure prone, it can’t provide cooling and I’m going to use it 10% of the heating hours? No thanks!

Jamie Hall

yeah, well…

Steamhead

@Hot_water_fan , I am going to be comfortable that 10 or whatever percent of the time. That's why I have a boiler and radiators.

EBEBRATT-Ed

@stembo

The best advise you will get on this forum is to call @EzzyT , or @clammy or @JohnNY for your boiler replacement

Hot_water_fan

@Steamhead people have different preferences. Some people love steam. Most are indifferent.

leonz

Speaking as a homeowner, I always loved steam heat because I grew up with it. The apartment over my parent's grocery store had a one pipe steam system with cast iron radiators and the boiler was the size of an end table/typing table on wheels.

I wish I had steam heat now using my coal stoker boiler.

I would want to know if the old boiler is leaking before you do anything.

As you have the steam heat already installed and you know the header plumbing is incorrect perhaps it would be a good idea to have an estimate done for the replacement of the badly designed and installed header and at the same time a smaller burner and a double drop header to replace the bad header and install a pair of low water cut offs to protect the boiler since B+G recommends having a pair of them for a steam boiler installation. You have not mentioned how old the boiler is or what it has for controls; perhaps it would be a good idea to install a new main vent or vents, pressuretrol and pig tail or vaporstat, and new gauges as well as having the boiler cleaned of muck from the steam chest?

Having a new smaller boiler installed would require new controls, a water feeder, 2 low water cut offs new gauges etc. to begin with so maybe just doing the repairs like installing the new controls and low water cut offs and upgrading the old boiler with a smaller burner, the new double drop header and new vents for the main and the radiators would make more economic sense if the boiler is still sound and just down firing/installing a smaller set of gas burners, smaller oil burner or smaller propain burner is the better way?

If you could provide some images of your existing boiler, the controls and the vents that would help the steam folks that are members of the forum help them to help you to make a rational decision about you existing boiler.

BobC

The cost of fuel to get heat where you want it is one part of the equation. now we have to consider the cost of upkeep. i clean my flame sensor every year on my gas boiler, check all the safeties and run a combustion test after with my flue gas analyzer

I do most of the routine work on my steam system myself. I bought this palace in 1981, since then outside of yearly cleanouts when I had oil I've ONE service call in 43 years. With a condensing boiler or heatpump you are going to need more service calls and those service calls are going to cost money.

Make sure you understand this before jumping ship. i kept the steam and added a heat pump that I use for cooling and heat on mild winter days. In 10 tears I'be paid aout $900 on heat pump repairs and $0 on steam system repairs.

Bob