Brooklyn brownstones are very valuable properties, so my first advice to you is to do the renovations properly and in line what is being done to the other brownstones on your block.

If it were my house, and I wish it was, I would convert the boiler from oil to gas and keep your old radiators. Gas is the cheapest fuel right now and will be for the foreseeable future. You can install a high efficiency boiler which will probably be a less than half the size of what your currently have. Going all electric may be attractive, but you will not be happy when get your first electric bill. If you are curious about costs of gas versus electric then post the respective rates so a calculation can be done.

For cooling I would recommend installing mini splits. I say this because I doubt you have the room to install duct work unless you are willing to install chases and lower ceilings. The mini splits are probably the most cost effective solution. You could probably get away with having one head in the front of the house and one in the back. That would be adequate for cooling, but not enough for heating if you did away with your boiler.

@fsq4cw I am intrigued by this concept - can you explain how it works for cooling? Does it send chilled water through the radiators? If so, does this cool an entire house? How would it remove the humidity from the air that makes the summer heat so unbearable?

And for heating or cooling, what kind of electricity does a system like this draw? We are absolutely interested in keeping the radiators for aesthetic value and for their effectiveness at heating, but are turned off by the cost of updating both them and adding mini-splits for cooling so we would love to find a way to keep them without needing to install a separate cooling system!

@mike_home We are definitely concerned about the high electricity costs as compared to gas, but are also operating in a time and place where this city is making it extremely difficult and unpleasant to do any updating to gas service, as they are trying to discourage gas usage (similar to the natural gas-ban that was put in place by California). In terms of mini-splits, this is actually the system that we were looking at (though we could also do ducted by dropping the units into closets and bathroom ceilings), but even still the costs feel prohibitive. We've been quoted for oil-to-gas conversion roughly $25-30,000 and HVAC (Mitsubishi hyperheat condensers for heating and cooling) between $40-60,000 (wall-mounted vs. ducted ceiling cassettes). Do these costs feel consistent with what you've seen or heard?

You already have a gas meter, so I would think installing a gas boiler would not be an issue with NYC. Then again Gov. Cuomo seems to have an agenda to stop any new gas pipelines. One would think switching from fuel oil to natural gas would reduce the carbon footprint.

The $25-30K for the gas conversion seems high. However it is difficult to estimate the amount of work involved. I suggest getting more estimates and a detailed proposal of the equipment to be installed and the work to be done. Spring is the slow season so it is a good time to do large HVAC projects. If you post your oil and gas rates we can calculate the operating costs of each. The return on investment by switching to gas may surprise you

The $40-60K for the Mitsubishi equipment is absurd. I know you like the idea of an integrated heating and cooling system, but the price may be steep. I suggest you get quotes for cooling only mini-splits. If you are going to keep the radiators and you are OK with wall mounted cassettes, then I don't seem much of a down side other than having a second thermostat. You could install the cooling equipment in the spring, and then work on the heating in the fall

Retrofitting a house that has cast iron radiators with an air-to-water heat pump represents the best situation for a project like yours because cast iron radiators (emitters) generally use the lowest Entering Water Temperature (EWT) produced from a heat source – except for properly designed low temperature in-floor radiant. Aluminum fin radiators require a water temperature from 160˚F to 180˚F. Cast iron requires a water temperature of 140˚F. The lower the water temperature required, the easier it is to accomplish with a heat pump, the less energy required and the more money saved. There are high-temperature heat pumps that do generate hot water up to 160˚F but generally these are geothermal and non-reversible (no air-conditioning).

Using an air-to-water heat pump in the case of your building would mean that all your existing (cast iron) radiators would be plumbed to a Heating Only circuit (zone) of the output of the HP. This is because the existing supply pipes and radiators would ‘sweat’ in cooling mode, creating conditions we don’t want.

Since you want air-conditioning and that the supply water temperature with a HP in heating mode would now only be about 120˚F, supplemental hydronic fan coils (for heating & cooling) are required. These are on separate zones, designed for heating and air-conditioning, fed with hot or chilled water, piped with Armaflex insulated piping where neither the pipes nor the fan coils sweat and will additionally make up for the lost Btu due to the lower water temperature. In cooling mode, the condensate from the fan coils is collected and properly drained as in any other air-conditioning system.

The cast iron non-insulated piping and radiators are switched ‘OFF’ during cooling mode by switching ‘OFF’ either the circulators (pumps) or zone valves controlling the water flow to these ‘heating only’ zones to avoid any problems created by condensing water vapour.

Some but not all of the advantages of this type of system include one heat pump able to provide efficient heating and cooling, domestic hot water (DHW) heating, possibly including on demand domestic hot water heating as a priority, simultaneous heating and air-conditioning if so configured, easily zoned - including zones requiring different water temperatures.

The use of a buffer tank(s) for hot and/or chilled water means that you can have very small zones, such as a small bathroom in-floor hydronic heating or a bathroom hydronic towel rack as a separate zone without short-cycling of the heat pump, as the heated water is drawn from the buffer tank without the need to run the HP till the tank temperature drops below a pre-determined minimum that would then require a longer, more efficient run time.

Unlike mini splits, these systems are designed and built more like commercial equipment that when installed with a proper design should last a very long time and add considerable value and comfort to your property.

The same system with a geothermal source, while being more expensive would also be more efficient. Air-source will work fine. Either system is a premium system with a premium price tag. Factor in the price differential of the different systems available including installation, operating, maintenance and life cycle cost.

Something to keep in mind & a reason to ‘Think Water’:

"A given volume of water can absorb almost 3500 times a much heat as the same volume of air, when both undergo the same temperature change."

3/4"tube = 20"x12" duct

3/4"tube = 18" ø duct

I find NO fault with mike­_home’s suggestions; different approach, different philosophy, different cost. Although your costs seem to be high no matter what you do.

BTW: As you are in Brooklyn, I’ll mention that as a geothermal professional, I was invited to tour a massive institutional retrofit geothermal project in Manhattan where they converted hydronically heated heritage buildings that are well over 100-years old to a system that is basically as described above except with geothermal. They probably by now have saved millions of dollars on energy and maintenance and never dreamt they could have zoned air-conditioning as well. To give you an idea of the scale of this project the boreholes and there are many, have diameters measured in feet with each one drilled down to a depth of 18-hundred feet (1800ft) through solid Manhattan rock!

Sadly, after 9/11 it has become more difficult to visit this type of critical infrastructure.

IMPO

SR

Hi I have a old home on the metro north line in Connecticut so labor is a bit lower perhaps and my home is a bit smaller. We added a high efficiency boiler to our existing hydronic radiator system. I hate heat blowing so wanted to keep the rads. We spent just under 22k for that five years ago.

Then three years ago we added the mitshibitsi mini split with heat pump system you are looking at . Our house's original heat was just one zone and in early fall and spring just heating one floor vs all floors was appealing. We have a ducted system upstairs and wall mounts on the two lower levels so that we did not need to lose valuable closet space. This cost us 20k to install. I hate the wall units but only have to look at one on my ground floor regulary. It is super quiet and works well at cooling.

We very rarely turn the heat pumps on for our boiler is so efficient and gas is very cheap.

@fsq4cw - I'd love to see/hear more about your experience using geothermal in conjunction with an existing hydronic heating system--for heating, cooling, and domestic hot water. I'm rehabbing a lovely 97 year old single family Dutch colonial revival on a large (1/3 acre) lot in Seattle. Originally a coal-burner converted to oil, it's otherwise the original gravity system. The house isn't plumbed for gas, and rather than the cost of trenching for new gas service (I was considering a combination condensing boiler), it seems like it might make sense to invest in the geothermal source instead. Can you help get me pointed in the right direction? Thanks in advance for your help!

Re: Pete Holmes

I would imagine the existing hydronic system has large floor standing cast iron radiators, no circulator (pump) and a has section of the hydronic system at the highest part of the building that might be open to the ‘sky’ (non-pressurized). Unfortunately the only part you may be able to keep would be the hydronic radiators but even that would be significant.

There is a quiet revolution happening in HVAC that you won’t hear much of on this site as it is mostly stuck in the past with air-source HP, gas furnaces and central forced air. The first phase back to Hydronics began with geothermal water-to-water heat pumps because in addition to clean high-efficient performance, they were reversible and that made air-conditioning possible with 1-integrated system in the residential market albeit at a premium price. What is currently happening is the introduction of high-efficiency, low outdoor ambient temperature air-to-water heat pumps that will become a game changer back to hydronics for new custom homes and retrofits for homes, particularly heritage homes that still have hydronic heating.

What I would suggest that at the very least, have a hydronic system designed for both heating and cooling but with a heating water design temperature as low as 95˚F. Regardless of what you do today you will be ready for the future that will certainly be with heat pumps and low temperature water. A reversing water-to-water geothermal heat pump that you are planning for will be able to heat and air-condition your home as well as be able to generate your DHW. I have seen construction where rather than backing up the geothermal HP with an electric boiler the backup is an air-to-water HP so that they have the redundancy of an electric boiler but that depending on the outdoor ambient air temperature in the shoulder season, the air-source HP might in fact be more efficient than the geothermal when compared to ground temperature. The system automatically reverses the priority when this condition exists and the air-source HP becomes primary and the geothermal becomes the backup. BTW: Your ground temperate in Seattle is 53˚F.

I would suggest contracting with a mechanical firm that has experience in both the commercial and residential hydronic heating and cooling industry. You might have to contract separately for the geothermal but that would be OK as long as the coordination and communication is good between contractors and their installers.

I have done this (Geothermal-to-Hydronic) for clients that are satisfied with the system and the result as far as I know, as the feedback is still good whenever I have touched base with them; they have not called me. We have DX-to-forced air geothermal in our home that will this summer be starting its 18th year since installation with no breakdowns and requiring very little routine maintenance.

These are high-end systems – particularly geothermal water-to-water hydronic systems, unmatched for comfort, zoning capabilities and efficiency. A given volume of water can absorb almost 3500 times a much heat as the same volume of air, when both undergo the same temperature change. A 3/4in tube distributing water is equivalent to a 20in by 12in duct or an 18in ø duct.

Many will say that you will not see a payback. That is not necessarily true. You will be building a Tesla in your basement and while there’s no likely payback with a Tesla people still do buy them!

IMPO

SR

With apologies for the long, long hiatus, I want to first thank you for your very, very helpful response, SR. You gave me a lot to think about; between your response and pandemic delays, I've been forced to slow down on this rehab project and fortunately avoid some bad decisions. In the meantime, I've proceeded to focus on replumbing and rewiring, honoring Arthur Loveless' 1923 Dutch Colonial Revival design--we found the original, signed & stamped blueprints inside AFTER closing!

I'm going to rely on the original gravity hot-water radiator system with its oil-fired boiler (originally coal-fired) one more winter season, then make the switch in 2022. Because of Seattle's milder climate year round, I recognize the the additional capital cost of a ground source heat pump doesn't make sense. I'm sold on the air-to-water heat pump, intending to both preserve the legacy radiators and add cooling capacity for our increasingly warmer summers, in addition to domestic hot water production via desuperheater or standby tanks. I'm also open to a gas hybrid system, now that gas service is available. We'll probably go with a dual fuel range and gas fireplace insert for power outages. (I drive a Chevy Volt, btw, so I recognize the value of hybrids and transition fuels to better address global warming.)

In addition to the Chillix and Nordic air-to-water heat pump systems you referenced, I'm looking at LG's Therma V, NorAire, and Daikin's (discontinued) Altherma split units. The basement and attic are both unfinished, so accessing both floors with recessed heating/cooling fan coil units is pretty straight-forward. My biggest concern is how the US lags the EU and Asia for such systems, both technologically and in terms of tax incentives. What's your latest thinking on viable systems for my situation, since your last posting?

Thanks in advance for your thoughts!

Sorry, this is @fsq4cw, and I meant Chiltrix!

Re: Pete Holmes

I would not worry that North America lags EU or Asia. Many, perhaps most large commercial buildings are today hydronically heated and cooled for reasons of energy efficiency. You just have to find the ‘right’ experienced, competent contractor with a proven record in the latest techniques of efficient hydronic design (with the latest professional software), installation, commissioning and controls for both use and monitoring.

I personally would keep the cast original iron radiators if that were possible, however that might depend on their internal condition with regard to sedimentary deposits and supplement the heating with lower temperature heat pump supplied water by adding strategically placed fan coil units for both make-up heating and air-conditioning.

You might want to at least speak with a professional mechanical engineering company (commercial) to further explore your project and to see if they might have recommendations for competent contractors in your area. You might also contact professional HVAC associations for information and possibly contractor recommendations regarding hydronic heating and air-conditioning.

I do like the Nordic air-to-water systems as they are designed and built in North America more to commercial standards. Even the best equipment will fail to perform and live up to expectation if improperly installed; proper design is everything - especially with hydronics!

Good, open communication between the contracting installer and the system designer is absolutely essential to avoid serious and expensive problems, as installers must seek clarification of any/all design elements seen on drawings that they are not absolutely clear on and sure about!

Regarding energy efficiency (comfort & zoning), hydronics are to the distribution side of heating and cooling what geothermal is to the supply side of the equation - when properly executed.

IMPO

SR