Replacing gas Navien boiler with electric boiler for hydronic heat?

acustode · May 14

We have radiant floor heat throughout our newer ranch home in Colorado and our boiler is a Navien NFB 200. We are going to be putting a solar PV system on our roof this summer. Propane is somewhat expensive. We are evaluating whether it makes sense to replace the propane Navien and replace it with an electric boiler for hydronic heat. Has anyone done this and if so, what electric boiler brands would you recommend? Things to beware of??? Thanks in advance, you are all so helpful and I appreciate it.

mattmia2 · May 14

did you do the math on the energy you need from the solar for resistance heating? do you have a way to store the energy during the dark periods and nights? an air to water heat pump would use less energy but would still need a lot of energy.

JMWHVAC · May 14

I would not REPLACE the propane boiler. If you want to use electric, ADD an electric unit then you have more options.

hot_rod · May 14

there are actually controls that can switch back and forth between the propane and electric. Both when you have available PV, or if you have off peak rates.

I’m in Utah on Rocky Mountain Power. Their TOU, time of use program has 6.0 Oct-May, 7.1 June- Sept.

See if your utility has a program.

Then go here and. Insert the costs.

Make sure the cost is actual delivered cost with all the tax and fees.

LP is a fickle fuel to get a price on, as you may know

https://coalpail.com/fuel-comparison-calculator-home-heating

TheUpNorthState88 · May 14

I would add the electric and switch between the two when the costs are best. I would not go ripping out a perfectly fine working propane boiler and switching to all electric.

Jamie Hall · May 14

Unless your house is extremely well insulated or has a very high passive solar capture, and the capability to store two or three days of energy…

Nope. Never mind the price. Do your sums on energy and power requirements. Just to give you a number or two to play with, your peak power output from a photovoltaic collector will be around 20 watts per square foot of effective area at noon. Now Colorado is pretty sunny, so on a good bright winter day you could expect to collect around 100 watt-hours of energy per effective square foot of collector. Spread over 24 hours — which assumes you have a battery bank to store the power — that works out, if you are lucky, to around 4 watts available power — 13 BTUh. Now scale that back a bit to account for the fact that unless you are using tracking panels, the effective are is considerably less than the physical area of the panel.

Add to that that it is unlikely that the panes would cover the whole roof, although I have seen such designs.

And you have a pure power and energy problem, just from the power supply standpoint.

Now factor in that you need to store that power at least overnight. Yes, battery storage is available. That's where you can start figuring money in; at least a couple of hundred dollars per kilowatt-hour.

It sounds so nice on paper… until reality hits…

hot_rod · May 14

How many square feet is the heated space?

How much PV?

The first number to begin with is the heat load of the home at design.

If it is new construction, well sealed and insulated, then load numbers could be in the low double digits. maybe single digits in BTU/ sq ft. numbers. In some cases internal gains and any solar gain will heat the home.

The lower the load of course, the more viable for alternate energy assist.

My 6.2 Kw PV in Utah covers my A2WHP 100% on sunny days.

An A2whp would double or more the electricity input, but electric boilers are a small fraction of the cost, so the economics need to be considered.

Jamie Hall · May 14

Not contradicting anything you wrote, @hot_rod — all correct. The joker in the deck is that second to last paragraph…

pecmsg · May 14

do you own the LP tank and can shop around or tied into a contract?

What size tank are we talking about?

How many times a year does it get filled?

Rearly is electric cheaper?

EdTheHeaterMan · May 14

https://forum.heatinghelp.com/discussion/comment/1896606#Comment_1896606

Rarely is electric cheaper unless you are getting it free from the sun. My son-in-law and daughter both have solar panels on the roof, and they both have electric vehicles. They never visit gas stations and “fill up the tank” while they are asleep. (They are ER doctors often on the night shift.) So there is time saved with that scenario.

I always get them a Gas Card for Christmas. That's the kind of Dad I am.

To the point. the Solar does make the electric less expensive in the long run. But still, I would keep the Gas Boiler and just connect the Electric Boiler or Air to Water HP next to the Gas boiler.

Jamie Hall · May 14

Oh I agree that solar PV does make electricity inexpensive in the long run — our 15 KW array will pay for itself in about 6 years. It does NOT make it a feasible source for the sole heating source for a structure, however.

acustode · 2:54AM

Thanks everyone for your input, this definitely helps. We meet with the solar company early next week but we do plan to have battery storage in addition to the grid tie. Our home is 2350sf ranch and super insulated with A LOT of sun. Perhaps a A2WHP would be better than an electric boiler since it would also provide us with a cooling function in the summer, which we don’t currently have (we’re at 8350’ elevation and blessed with cold nights). Hmmmm… lots to think about and I now see it’s not as easy as just pulling out the LP boiler and replacing it with an electric boiler. Thanks again.

hot_rod · 3:58AM

the hybrid systems are a good way to go if it is in the budget. This combines the lp boiler with the A2WHP. Most of these heat pumps have the back up boiler control function included. You program the parameters for when the lp kicks in.

Some heat pumps also have a resistance element to supplement, or cover 100% of the load if the hp goes down.

It’s all about crunching the numbers with actual data not marketing hype.

I’m about ready to see how chilled water through my radiant tube cools my place. It has been done successfully in the past in this super dry desert climate. I will have a provision to move some cooled air if necessary

If there was a radiant design done, most of these heat pumps info is there.

The load number on the coldest”design day”, that design day outdoor temperature, and the supply water temperature required at that condition.

120f and lower radiant supply may make the numbers work.

Passive solar helps a lot, even on design temperature days, it is your least expensive heat source. In some cases more than you need or want😏

Here is a good generic read on A2WHP design conditions

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water%20heat%20pump%20systems.pdf

Replacing gas Navien boiler with electric boiler for hydronic heat?

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