Understanding hydronic radiant heat, and a potential retrofit?

[zuren]

The wife has some concerns about the exhaust odor coming from our natural gas, forced air furnace. You smell nothing inside, but outside the exhaust has an odor. I grew up around propane and older natural gas furnaces and feel the odor is somewhat normal for a mid-1990s gas furnace, but we are having someone come out to check.

I'm posting because I can already see where this is going:

- wife hates the odor
- wife hates forced air heat in general (dry air, allergies, etc.)
- furnace is pushing 23-24 years old
- electric water heater is also quite old, and we have considered replacement

I'm preparing myself for the conversation to turn toward replacement of the furnace, and if that is the case, I would want to consider retrofitting some sort of hydronic radiant system for both heating the house and domestic hot water. Has anyone installed such a system in an existing house with access to the first floor in the basement?

My basement is partially finished, so I would have to tear out some ceiling drywall (which would not hurt my feelings; I hate finished ceilings in a basement that do not allow access). My thought to make such a project more affordable is that I install all of the tubing, then the heating company comes in to install the boiler/hot water heater, valves, etc. and make the gas connections. I have no idea if they would do this.

One of the biggest expenses, therefore one of my biggest questions, is do you use a hot water heater or a boiler to generate the hot water? I even find places where tankless water heaters are recommended. Opinions across the internet seem to vary, so I thought I would ask here.

One place I have found some info is this site where they recommend a Polaris water heater versus a boiler - https://www.radiantec.com/about-radiant-heating/open-direct-system/. The Polaris is a $3000 water heater, so definitely not a box store special.

Here is another link where I've gathered info to try to decide if this is something I get a contractor to fully install or are there DIY portions of this job - https://www.thisoldhouse.com/ideas/retrofitting-radiant-heating.

A retrofit to radiant heat would create the question of how do we cool the house if the forced air furnace is removed? Do we keep the furnace in place just for the central air, or is there a more elegant solution? (window A/C units are not an option as far as I'm concerned).

Thanks!

 

[Dana]

Tankless solutions are almost never the right solution, and not necessarily cheaper now that fire-tube condensing boilers have come down in size. The Polaris isn't really the best solution either, since it's more prone to short-cycling (unless you hack the controls, voiding the warranty.) The HTP Phoenix Light Duty with it's modulating burner is cheaper and better for most houses, but the HTP Versa is purpose-made as a combi-heater, with less design risk (but a higher price tag.) But there are good solutions to be had with the Light Duty (light duty only compared to bigger-burner commercial water heaters), in the hands of a decent designer.

Open systems are a generally bad idea, and even illegal in some states (not sure about MI.)

First things first: Figure out your design heat load. Since you have a heating history on the place, you can use the existing furnace as the measuring instrument to get a reasonably accurate handle on the heat load at the 99th percentile temperature bin for your location. Follow the methods detailed in this bit o' bloggery.

Done right that will tell you the whole-house heat load, more accurately than Manual-J or IBR methods, but it won't tell you what the room-to-room loads are. Using an IBR spreadsheet method, or an online Manual-J tool for room by room numbers you can figure out proportions.

With the room by room numbers you can the take the room with the highest load per square foot of available floor, and look at different methods of doing radiant to come up with a solution that can run the boiler at condensing temperatures most of the time.

Ductless mini-splits in the highest load rooms, sized correctly for the cooling loads can work pretty well. In some houses just one head/cassette in a centralized location will work. But until you know the loads, it's impossible to figure out the optimal solution.

Ductless or mini-ducted mini-split heat pumps could be a reasonable heating option too. The cfm of the blowers are a small fraction of what you get out of the typical 3x oversized 1-speed fossil-burner furnace, quieter than your refrigerator when running at low speed.

So, do your homework (initially on the whole-house load, then the worst case room's BTU/hr per square foot) and share what you've discovered. If you need more than 15 BTU/hr per square foot the radiation can be pretty expensive- more than the cost of the boiler/water heater if doing the whole house as radiant.

 

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[hj]

Installing the tubing PROPERLY is a key component of the job so I doubt that ANYONE would want to connect to tubing that is already installed.

 

[Jadnashua]

Radiant heating, properly installed, is probably the most comfortable method of heating a space. The floor covering used can make a difference as to how well it works. Done well, you can be comfortable with a lower overall temperature, which aids in the efficiency.