HVAC installer or engineer doing a load calcuation
I’d like to install a heat pump so I’m wondering whether it’s best to hire an engineer to do this or just trust the HVAC installer who has installed this many times on similar homes. I’ve talked to an engineer but was quoted a high price to do a load calculation: $4,000, so I’d rather not.
I know the problem could be that the HVAC installers could oversize it, create more work for themselves and then charge me more. But at the same time having an engineer give a calculation doesn’t guarantee anything either.
My house has a simple design in that it’s a rectangular two-storey 2500 sq ft, has no basement or crawlspace or attic (cathedral ceiling) and is built with solid block walls so it should be a lot more straightforward of a setup than a lot of houses.
I want to do exterior insulation and I want to install a heat pump. Would you just get a qualified HVAC installer to make the decision or hire someone else to do a thorough energy audit?
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If you are doing exterior insulation, size the heat pump based on the resulting insulation value. $4000 seems steep, there are places that will do a heating load for more like $500. Coolcalc is a popular one people here have used for a DIY method. I like the calculators on the Borst website.
I'd be a little skeptical of what the HVAC guys come up with. The one quoting an install at my parents house was oversized by 2 tons and he wanted to have it switch off at 40F and let the old propane furnace take over there. Decisions that make zero sense.
I have learned to never trust an HVAC contractor's load calcs. We are going through it on a current project, where their proposed system is more than twice the size of what my energy model says it needs to be. I would look for a less-expensive mechanical engineer.
Have you ever compared coolcalc or sim simple manual j to one of your energy models, I’m curious how similar/accurate that software is.
I have compared BeOpt, Borst, Coolcalc, and fuel usage numbers for my own house. They are all fairly close. All calculators seem to overestimate a little bit. Coolcalc is pretty user friendly and easy, but also has limitations. I couldn't figure out how to enter a double stud wall.
That’s good to know, thanks. Coolcalc is nice as it’s one of the easiest to use manual j softwares, which a few jurisdictions I work in require. I was just on their site and apparently the upcoming version will allow custom wall u value, which should make it much more usable for better than code houses.
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I think heat pumps are less sensitive to needing load calcs but it depends on how you install them. If you install multi unit system with a large outdoor unit and minisplit heads in each room, you will struggle.
But if you get a VRF system, then your turn down options are much better and you can get really small heads for each room.
If you’re installing an air handler, you at least need a competent hvac installer to size the ductwork and cfm per room but the moral of the story is to consider a VRF system.
Air handlers can be VRF too with variable speed (ECM) blower motors.
Did you leave room for the air handler and duct work in your plans?
If you are picky about the upstairs and down being the same temp getting separate systems would be a good idea.
Over sizing a HP is bad in hot and humid climates and with multi headed mini splits.
I was able to talk my HVAC contractor into installing the smaller heat pump I wanted by allowing him to oversized the backup heat.
Oversizing the electric back up heat has zero down sides. It is cheap to buy and install and if you don’t operate it cost nothing to own.
Walta
Good point. What electric back up heat did you go for? Zero emission boiler?
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