I can't comment on doing a conversion but I have to ask - is your house large, air leaky, poorly insulated, or some of each? Those are two very large boilers.

Good luck.

It is large (~3,000 sqft) excluding basement. I'm not sure if it's fully insulated. I believe the newer section of the house (incuding basement and garage) which is heated via hot water is insulated since it was built out/renovated in the early 2000s, but the older/original section of the house (steam radiators) likely isn't?

I was thinking exactly that! whether we even need a 250k BTU steam boiler if it's only heating up half the house... at max the sqft of the older section of the house would be ~2,000 sqft but likely something between 1,000-1,500 sqft?

thank you!

You need to make sure that whichever HVAC contractor you choose does a legitimate (ie, not fudged) heat load calculation. It's a calculation that considers a number of factors specific to the size of the home, its rooms, and its construction and not the least of which being where your home is located, to determine how much heat needs to be produced to keep the home comfortable when it's cold outside. Rule of thumb and rough approximation were used in the past and rounded up with the result that other than homes built by conscientious tradespeople like in the last 10 years, most homes have waaay larger heating and cooling equipment than they need. More isn't better, oversized equipment produces less comfort at greater cost than when the right sizes are determined and installed.

Again, good luck.

The steam radiators are two pipe systems. We're just not sure if we should just replace our steam boiler for a new one or convert to a hot water system if steam is a dying trade?

Based on the information you provided so far, it makes sense to convert the steam radiators to a hot water system. I would think it is feasible to use the current two pipes used for the steam radiators. The radiators themselves will have to be replaced. However it may be possible to plug the opening where the steam vent is connected, and cut new threads at the top of the radiator for a 1/8 inch air bleed valve.

It may also be possible to connect all the radiators to the current 150K BTU hot water boiler. A heat load calculation will determine if the boiler is large enough.

I would get three HVAC companies to give you a proposal. This is a major long term reno. Friends with an even older home have had lots of problems getting repairs to their steam system. They removed it. Newer parts of the house were fitted with hot air and ducts. Older parts now have heat pumps.

I would suggest getting quotes to convert your home to modern, energy efficient, low water temperature hydronics supplied by either an air-to-water heat pump or geothermal heat pump that would provide heating and cooling hydronically along with domestic hot water.

You would have to add low water temperature panel radiators to compensate for the lower water temperatures. The lower the required water temperature supplied the more efficient the heat pump becomes.

Energy and costs would be lowest when designing the source (hydronic heat pump) and the distribution (hydronics via low water temperature emitters) as desperate but complimentary systems.

Air-conditioning and domestic hot water can also be included.

Taco Air-To-Water Heat Pump

IMPO

SR

If the steam boiler is old and has frequent breakdowns or requires expensive repairs, it may be more cost-effective to replace it with a new, more efficient boiler. This will also ensure that the heating system is reliable and saf

It's not uncommon for older homes to have smaller chimneys that can't support larger commercial boiler repair. However, the suggestion to install a mechanism to ensure that both boilers never turn on at the same time might be a bit of overkill. You could get a second opinion on this issue just to be sure. In any case, it's always a good idea to consult with a professional before making any major changes to your heating system. They can help you weigh the pros and cons of each option and guide you in making the best decision for your home. Good luck with your decision!

If you're planning to stay in your home for a while, I suggest you begin with a home energy audit. Many utility companies offer them for free. The auditor can give you an idea what the biggest potential benefit will be--whether air sealing and insulating the older portion of your home or installing a higher efficiency heating system (there are multiple options) or some combination of both. They'll also be able to provide information about any rebates the utility offers for implementing energy upgrades. Once you're equipped with that information, you can speak with insulation and HVAC contractors to identify the cost of each alternative.