HVAC query: heat pump vs hydronic in an old house

[Roger Feeley]

My daughter has an 1860 house with hydronic heat installed in the 1970s. Upstairs are baseboard heaters. Downstairs, it’s under the floor. I’m told that the pipes are probably imbedded in thinset. Part of the building has a cellar and I don’t see pipes under the floor.

The house also has AC so there are forced air ducts everyplace.

At one point, we thought we needed a new boiler. I wondered out loud about abandoning the hydronic heat in favor of two heat pumps. The HVAC guy said no. He said that the heat pump would wreck the old building.

I just don’t understand. With a heat pump, I can add a whole house humidifier and better control humidity. The hydronic system circulates 150 degree water. Heat pump is much more gentle.

what am I missing?

[Roger Feeley]

Dang autocorrect! The thread was supposed to be H V A C.

[Jim Becker]

Dang autocorrect! The thread was supposed to be H V A C.

Fixed.

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You should probably ask the contractor to 'splain why there is the feeling that converting to a heat pump would "wreck" the old building, particularly given there is already ducting for AC in place. (Assuming it's correctly sized, etc.) Today's modern heat pump systems, including MiniSplits are really efficient, especially in your geography. (assuming your daughter is in a similar climate)

BTW, the humidification is no walk in the park...depending on your/her water supply, they can be "fun" to maintain. I abandoned ours years ago.

[Roger Feeley]

Jim, first, Thank you. I like to make the subject as informative as possible and making about flowers was kind of embarrassing.

yes, we all live in northern Virginia inside the beltway. In fact, we are in two houses on the same lot separated by a pool. The weather here can get a bit extreme but never for long.

And yes, I should make someone explain this. If it comes up again, I will.

[Jason Lester]

Maybe he meant ruin it aesthetically or historically? Doesn't make any sense to me either way though, especially if it already has central AC.

[Bill Dufour]

Maybe he means swings in humidity and temperature will cause wood movement and split old wood?
Bil lD

[Lee Schierer]

Heat pumps are also capable of supplying heated water to hydronic systems. My heat pump has the option to assist my water heater.

[Roger Feeley]

It’s just speculation but I think bill is right. The guy was concerned about humidity swings. But that makes no sense to me. I think I can control humidity better with a heat pump.

[Tom M King]

Radiant heat is more comfortable to me, than heated air, in an old drafty house.

[Bruce Wrenn]

Because the heat pump relies on moving HUGE volumes of air, most likely the existing duct work would have to be replaced. You didn't disclose the fuel source for current heating system. If it's natural gas, then it's a "NO BRAINER." Install a heat pump with a hydronic coil in plentium, or gas furnace for back up heat. Because you have two floors, you will need TWO separate systems with the heat pump. But, I'm with Tom. Hydronic heat in a old house keeps the whole living area comfortable. If I ever build again, I can promise you first floor will have hydronic, possibly from solar.

[Jim Becker]

I know the area...Professor Dr SWMBO grew up just inside the beltway in Falls Church on Executive Avenue and my "office" was in Fair Lakes prior to my retirement. :) Heat pumps should be very efficient in your area.

Bruce may be correct, however, that for a traditional heat pump, the existing duct work may be inadequate for the projected load.

[Roger Feeley]

We currently have two ac systems but they aren’t zoned strictly upstairs downstairs. There’s some really crazy mixing.

the thing that bugs me most about the hydronic system is that the pipes appear to be buried in thinset.

good thought about the ducting. I just thought that heat pumps in heat mode ran a lot. It never occurred to me that they also need greater flow.

[Jim Becker]

Heat pumps work for heat exactly the same way they do for AC...just in reverse. They are heat exchangers. Where a heat pump can struggle is with really low temperatures which is why they are not the best choice for say, northern Minnesota. This shouldn't be an issue in your area. Some have "expensive to run" auxiliary resistance heating elements, but that only comes into play in temps that are below the level that the unit can support. My MiniSpiit for the shop is good to -5ºF, but certainly isn't as efficient at that point and (fortunately) doesn't have the resistance feature... And actually, multi-zone MiniSplit is an option for your project, too. Yes, the interior units are visible, but these things can have extremely high SEER ratings and cost pennies to run compared to older, less efficient systems for both heating and cooling. There is also the option of a system with small, high velocity air distribution which is popular for "historic" homes/buildings where using regular duct work is nearly impossible physically, if not forbidden.

[Steve Rozmiarek]

Because the heat pump relies on moving HUGE volumes of air, most likely the existing duct work would have to be replaced. You didn't disclose the fuel source for current heating system. If it's natural gas, then it's a "NO BRAINER." Install a heat pump with a hydronic coil in plentium, or gas furnace for back up heat. Because you have two floors, you will need TWO separate systems with the heat pump. But, I'm with Tom. Hydronic heat in a old house keeps the whole living area comfortable. If I ever build again, I can promise you first floor will have hydronic, possibly from solar.


Bruce nailed it. A heat pump takes twice as big (nearly) ducts as a forced air conditioner. Get ready for a massively invasive duct update if you go that way which will likely require LOTS of demo and soffits. The way its done here instead is to add mini splits to a house with a boiler system instead of re-ducting. You have some heat pump advantage that way, but maintain that great hydronic heat. Also agree with Bruce and Tom about the quality of hydronic heat, it's the gold standard.

[Jim Andrew]

is this an old uninsulated house? I lived in one while building a new house on this property. It was probably 120 years old at the time, and had no insulation and original windows. You could sit on the upwind side and feel air coming in the window and was tempted to get a cigarette to light and watch the air exit the other side. Took a 500 gallon tank of propane per month. A heating system that warms objects rather than air in such a building would be much more efficient.