Heat Pump vs In floor radiant electric boiler

millcove

Hello, we’re in the process of planning for a new house build, which will be 1500 sq ft (one level) on a slab and I am trying to determine which heat source will be the most cost effective to operate. A 2.5 ton air to air heat pump is one option or a 12kw electric boiler (in floor radiant). I’m aware of the upfront installation costs of both systems and have a rough idea of what the operational costs of the heat pump would be but what I’m having hard time understanding is what the operational costs for the electric boiler would be in order to compare. We are located in Nova Scotia, Canada and our heating season is 5 - 6 months of the year with a current energy rate 17 cents per kWh. Thanks

Jamie Hall

Very roughly speaking, the energy cost of the infloor radiant will be about 3 times the cost of the heat pumps.

Or to put it another way, they both use electricity, but the electric boiler uses about 3 times as much per BTU delivered to the structure as the heat pump, and the number of BTUs you need is determined by the structure itself, not the heating source.

GroundUp

An air-to-air can't do radiant. Each kW of electricity used for a resistance boiler would yield 3412 BTU and a heat pump would be 2-3x that amount, depending on outdoor temp. If your annual heat loss were 34,120,000 BTU, the electric boiler would cost you $1700/yr while a heat pump would cost $600-1100

DCContrarian

With modern construction I would expect a 1500 SF house to be in the 15,000 BTU/hr range, a two and a half ton heat pump seems oversized by about double.

At that heat load the floor only has to be about 5F warmer than the room to meet the load on the coldest days, on average days it would only be a few degrees warmer. You're not going to get the toasty toes you expect, it will be virtually unnoticeable. Heated floors are most dramatic in old, leaky houses with high heating loads.

If you decide to go with the resistance heat, there's no point in going with a boiler and tubing in the floor, resistive wiring in the floors gives the exact same efficiency with a much lower cost of installation and greater flexibility.

pecmsg

that 2-3X is based on a relatively mild ambient temperature.
the closer to “0” the lower it is. 1.5 or less.
Add in a few defrost cycles and that number may be even lower

Has to look at the low ambient operating costs

Robert_25

This sounds like a good application for an air to water heat pump. Search for info on “monobloc” heat pumps.

millcove

Thanks for feedback, avg winter temps here for dec/jan/feb is a high of +2 to low of -8 degrees Celsius, although there are the odd one offs of lows -15ish but those are becoming less and less frequent it seems. I did reach out to inquire about air to water and local contractor didn’t appear to be too impressed, still waiting to hear some more feedback from other contractors. With our constant hikes in power rates I just want to make sure I get this right. Thanks again.

Hot_water_fan

Ducted air to air is the way. If you ever need AC, it can do that too. No compelling reason to mess with hydronics on a low load new build.

GroundUp

https://forum.heatinghelp.com/discussion/comment/1810451#Comment_1810451

You've never been in a low load new build with radiant floor heat, have you?

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1810485#Comment_1810485

I have. What's your point?

ethicalpaul

https://forum.heatinghelp.com/discussion/comment/1810451#Comment_1810451

”if” is looking pretty optimistic here 😅

people are understating the operational cost savings of a heat pump in this thread, especially given the author’s stated temperature range. This happens a lot here. Note the OP is using Celsius.

I agree with @Hot_water_fan, the included AC capability of a ducted heat pump combined with its 75% lower operating cost seems like the obvious choice here. Your area may have incentives as well to consider.

Jamie Hall

Since this is a new build, and given the location, I'd go with ducted air to air heat pump too plus as much passive solar as I could on the site!

GroundUp

https://forum.heatinghelp.com/discussion/comment/1810489#Comment_1810489

My point is that the comment suggesting not to mess with hydronics was a bit silly. Low load or not, a slab on grade home in a heating dominated climate will always be more comfortable and efficient with radiant floor heat. I do agree that a ducted HP system is fantastic, for summer and shoulder seasons, but radiant can't be beat during winter regardless of the load.

Hot_water_fan

I don’t think having a concrete floor that’s 74F instead of 70F is worth the expense and complexity for only half the function. Reasonable people will disagree.

If the floor heating source is a resistance heater, then it’ll also cost 3x as much to operate.

ethicalpaul

At least 3x. Plus won't there be more heat loss into the ground due to the increased temperature differential at the floor with in-slab radiant?

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1810513#Comment_1810513

The claim that a heated floor is inherently more efficient than an alternative way of delivering the same amount of heat is just not true. It was frequently made in the early days of heated floors, but you don't hear it much any more because the evidence isn't there.

millcove

Thanks very much for all the insight and knowledge. Sort of a daunting task for a layperson like me to understand the full picture when making a decision like this when trying to compare the two systems.

Teemok

When considering air to water HP in cold climates a units peak capacity must be ignored. Capacity drops substantially in the deep cold. A heated slab offers great thermal stability and comfort as well as low system return water temperatures. If the radiant design shoots for the lowest return water temperature possible the COP can be in the 2 range at -8C OAT. For OAT's near 0C closer to 3 is possible. HP really wins in the shoulder temperatures above 0C. The more hours operated in that range the better a heat pump looks.

As said above the comfort from heat radiating from a slab to heat a space is great but the floor, by touch, won't be the idealized toasty warm surface most people think of. The floor won't suck the heat from you either. The desired flooring plays a roll in this choice. The blower equipment space, noise, ducting, vents, grill noise and air currents must be considered while looking at air to air if not going duct-less. If you are thinking ductless the fan units must be in your design atheistic. These are the costs of cooling. The need or desire for cooling is a prime factor in design choice. Ductless air to air HP can't be beat for investment dollar for both heating and cooling. Is it the best heat? Many argue it's not. How important is that to you? If heating mode is the the vast majority of the season, weighing the quality of heating vs the ability to cool for a tiny % of the time is a hard call. A HP radiant slab with good cooling is possible with chilled water mini split style ductless units or with a duct system for added money and complexity. Budget, aesthetics, simplicity, comfort, deep cold performance, cooling, there's a lot to consider.

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1810516#Comment_1810516

I would argue that deliberately putting a concrete floor into your house is a major hit to comfort. I'd much rather have a wood floor and ducted heat. Concrete is just a really lousy residential flooring.

pecmsg

slab on grade is a cold floor no mater air or water heat.
insulating that slab helps but doesn’t elements cold spots.

Teemok

A slab is not always cold. Preferences! Fast, durable, quake safe, easy to clean and can be nice and warm and potentially beautiful. The thermal mass of a slab is a great architectural feature. I'm no great fan of concrete as a building material so I could easily do without the benefits of a slab. If a slab on grade is the design, insulation is wise/required on it's own and putting pex in it is relatively cheap. Heating with it works beautifully in long term cold climates. It's almost invisible and silent. Low drafts and nice and even if done well. To each their own. My favorite is a guy eating a hot dog and jumbo corn sryup telling me living with radiant heating is gonna make me so sick.

hot_rod

with a slab on grade you will want to insulate it regardless if the heating type

At that point the cost if the pex is all you need to have clean, quiet , comfortable radiant system options

If you use pex you have many heat source options electric boiler , heat pump, wood, lp, solar

Find a knowledgeable local contractor to run some load numbers and give you options

I met a handful of knowledgeable hydronic contractors in your area on a recent training visit up there.

Hannah, at macleodandgrant.com could probably get you some names

Robert_25

it doesn’t have to be all or nothing. If going with a ducted heat pump, electric resistance radiant in the bathrooms would be a nice feature.